CityU Physics Annual Report 2022

CityU Physics

Message from the Head 2 The Department 3 Vision and Mission 5 The Faculty 6 Major Milestones 10 Success Stories 12 Awards 14 Fellowships 15

BSc Programme in Physics 17

MSc Programme in Applied Physics 19 PhD Programme in Physics 20

Major Research Grants 22 Research Highlights 23

Research Group Results 26 Research Centres 36

Events and Professional Services 38

Community Outreach 40

Exploring the Frontiers of Physics

It is my pleasure to introduce the first Annual Report from the City University of Hong Kong Department of Physics. We hope it will become a vehicle to connect with students, faculty, alumni, and our friends and partners in Hong Kong and beyond.

CityU Physics was established in 2017, following the split between the Department of Physics and Materials Science. As we celebrate our fifth anniversary, it is refreshing to reflect on how far we have come. Starting with just 12 faculty members, the department expanded rapidly by actively recruiting top talent from around the globe. Today the faculty comprises 26 outstanding scholars, whose seminal research is respected by the international science community and published in prestigious academic journals.

Thanks to steadfast support from the university, CityU Physics has developed the critical infrastructure necessary to conduct cutting-edge research on the frontiers of physics. For example, recognising the department’s strength in neutron scattering science and technology, the university founded the Centre for Neutron Scattering (CNS). Neutron scattering research at CityU has already led to major advances in a variety of areas such as clean energy, pharmaceuticals, nanotechnology and materials engineering.

The combination of an energetic faculty and state-of-the-art facilities is enabling CityU Physics to fulfil its education and research ambitions. The Department is currently on a mission to reform the curriculum, teaching not only foundational courses in physics, but also technology-enabled courses that tackle difficult physics problems. The ultimate goal is to equip students with the critical thinking and learning skills that will serve them well, whether they choose to pursue advanced studies or enter an increasingly competitive job market.

In spite of the disruption caused by the COVID-19 pandemic, CityU Physics has managed to overcome the challenges and put the department on a firm footing to face the future. Going forward, we aim to continue adding faculty members in critical areas. And, as the world opens up and travel resumes, we will also re-engage and strengthen our connections with partners in mainland China and the international community.

In the meantime, we hope to hear what our students, faculty, alumni, and our friends and partners think about our progress as we continue to build out a leading physics department in the Asia-Pacific Region.

Prof. Wang Xunli Head of Department and Chair Professor of Physics

CityU Physics - Light Up the Future

Today’s tech-driven world, and tomorrow’s sustainable society have one thing in common – they both depend on a deep understanding of physics to unlock and harness the fundamental properties of our universe.

Launched in 2017, CityU Physics is one of Asia’s most agile and innovative physics departments. With state-of-the-art facilities such as Hong Kong’s only lab for neutron scattering, which is operated jointly with the Chinese Academy of Sciences, and an internationally recognised faculty, the department is becoming a centre of gravity for physics excellence.

Although the department recently celebrated its fifth anniversary, it is not a newcomer. Building on the foundations of the original CityU Department of Physics and Materials Science, it has achieved critical mass and is now a regional leader in five key research areas. These include Atomic,

Molecular and Optical Physics; Quantum Materials, Soft Matter and Biophysics; Spectroscopy and Imaging; and Theoretical and Computational Physics.

In a recent assessment by the Hong Kong’s University Grants Committee, CityU Physics was ranked No.1 in world-leading (four-star) research output in physics and astronomy.

Nurturing the Next Generation

Located in the heart of Hong Kong – where East meets West and classical traditions mix with contemporary values – CityU Physics is a perfect fit for students looking

for challenging and rewarding learning experiences, and international candidates exploring new frontiers.

A robust curriculum combined with a lively and collaborative culture are the ideal formula for a successful future. The department is continually strengthening training in fundamental physics, to give students the knowledge needed to explore specialist disciplines. The latest additions include courses on soft matter physics and new modules that focus on the unlimited possibilities of A.I. and machine learning.

Each undergraduate is assigned a personal academic advisor from the faculty, who guides their studies. Initiatives like the Undergraduate Research Attachment Scheme offer students the chance to gain first-hand experience on cuttingedge projects, while others broaden their educational and cultural horizons through the Outbound Student Exchange Programme. The curriculum is also the perfect platform for PhD candidates conducting theoretical or experimental research, with more than 20 PhD students choosing CityU Physics for postgraduate studies in 2022 alone.

The data is undeniable. In addition to demonstrating superior academic performance, each year top CityU Physics students continue their academic careers at some of the world’s bestknown institutions – including Columbia University, Northwestern University, King’s College London and the Chinese Academy of Sciences. Many others enter the commercial world, joining the ranks of the biggest and most imaginative enterprises, to make their mark and change the world.

Attracting the Most Talented Teachers

The CityU Physics faculty attracts many of the brightest minds in the academic world, including APS and AAAS Fellows and winners of MIT’s annual, peer-reviewed Technology Innovators Under 35 awards. The energy and enthusiasm of this young faculty is infectious, and has a powerful influence on how students learn, grow and succeed.

Targeting talented teachers has boosted the department’s professional standing, enabling it to measurably outperform other local physics departments in independent

assessments. It also produces a steady stream of original, high-impact research which is regularly featured in respected academic journals, such as Nature, Nature Materials, Nature Communications, Physical Review Letters and Science Advances.

Focused on the Future

Armed with a talented team and solid support from the university, CityU Physics is turning a unique strategic vision into a real-world reality. It is making a measurable difference in physics as well as in the lives of students, faculty, society, and the wider world.

Unlocking the Secrets of the Universe

When the City University of Hong Kong decided to split up the fast-growing Department of Physics and Materials Science, it created an unprecedented opportunity – a chance to design and build a dynamic new physics department from the ground up. Staffed by an energetic, internationally recognised faculty, CityU Physics follows a clear and concise vision, supported by a simple forward-looking mission:

Vision

• To become a leading physics department in the Asia-Pacific region known for its professional curriculum and signature research

A Snapshot of Success

Leveraging Hong Kong’s unique culture, the resources and strengths of the university, and growing opportunities in the Greater Bay Area, CityU Physics targets five specific focus areas to attract outstanding talent. These include:

• Theoretical and Computational Physics

• Spectroscopy and Imaging

• Quantum Materials

• Soft Matter and Biophysics

• Atomic, Molecular, and Optical Physics

This strategy has worked well for the department, which now includes a 26-strong team with deep expertise in their respective specialties. Five members of the internationally recognised faculty are Fellows of the American Physical Society, and another is one of the Innovators Under 35 identified by the MIT Technology Review.

CityU Physics students are also doing well. For example, Mr. Chen Bowen, an undergraduate in the Joint Bachelor’s Degree Programme with Columbia University, was recently awarded two

Mission

• To provide rigorous training that prepares students for competitive job opportunities or advanced studies

• To become a recognised international leader in specific areas of research

• To serve as a central resource for physics education at CityU

prestigious scholarships – namely the William Strong Scholarship Fund for the 2021-2022 academic year and the Richard Stockton and Frances Rojack Scholarship for 2022-2023.

Under the supervision of their faculty advisors, CityU Physics PhD students are carrying out world-class research. Many of these students have published their research in prestigious academic journals, such as Physical Review Letters.

A Talented Team Taking CityU Physics to the Top

CityU Physics has quickly built a world-class faculty which has made it a leading player on the region’s teaching and research landscape. The growing body includes talented, internationally recognised individuals who are shaping young minds and producing high-level research that appears in respected academic journals.

Leadership

Associate Head of Department and Associate Professor Dr. Sunny Wang Xin PhD Columbia University, USA

Chair Professor of Physics

Prof. Bao Wei PhD Johns Hopkins University, USA

Chair Professor of Physics Prof. Jeff Ou Zheyu PhD University of Rochester, USA

Chair Professors

Chair Professors

Associate Dean (Internationalisation) of College of Science and Chair Professor of Physics

Prof. Ren Yang PhD University of Groningen, Netherlands

Associate Dean (Research) of College of Science and Chair Professor of Physics Prof. Zhang Ruiqin PhD Shandong University, China

Professors

Professor

Professor

Professor

Prof. Peter Yu Kwan-ngok PhD University of Hong Kong

Professor Prof. Chu Sai-tak PhD University of Waterloo, Canada

Prof. Chan Kwok-sum PhD University of Hong Kong

Prof. Yu Kin-man PhD University of California, Berkeley, USA

Associate Professors

Associate Professor Dr. Rosie Chu Xiangqiang

PhD Massachusetts Institute of Technology, USA

Associate Professor Dr. Hoi Io-chun

PhD Chalmers University of Technology, Sweden

Associate Professor Dr. Condon Lau

PhD Massachusetts Institute of Technology, USA

Assistant Professors

Assistant Professors

Breakthroughs and Achievements

For a relatively young department, CityU Physics has made some remarkable accomplishments in a variety of areas. In addition to conducting seminal research, the department has also made breakthroughs in education and professional services that are contributing to the development of Hong Kong society. This is particularly impressive for a department where more than half of the faculty members have joined within the last three years.

10 out of 26 faculty members were listed in the Stanford University “World’s Top 2% Scientists” ranking released in October 2021 (Prof. Bao Wei, Prof. Paul Chu, Prof. Jeff Ou, Prof. Ren Yang, Prof. Wang Xunli, Prof. Zhang Ruiqin, Prof. Chu Sai-tak, Prof. Yu Kin-man, Prof. Peter Yu, Dr. Li Xiao).

Prof. Wang Xunli was awarded the Croucher Senior Research Fellowship in 2021 and elected as a Fellow of the Neutron Scattering Society of America.

Prof. Ren Yang was awarded a prestigious “Global STEM Professorship” from the Government of the Hong Kong Special Administrative Region.

In a first for CityU Physics, a team of three undergraduate students won the Hong Kong Preliminary of the PLANCKS 2022 competition organised by the youth section of the German Physical Society (jDPG).

A few of the milestones that are putting CityU Physics on a trajectory to become a world-leading physics department are highlighted.

Dr. Denver Li Danfeng was listed in the MIT Technology Review’s Innovators Under 35 (China).

CityU Physics hosted numerous international workshops and conferences, featuring world-renowned experts, including the annual Celebration of Physics Symposium which has become a department tradition.

11 CityU Physics undergraduates have been admitted to the Joint Bachelor’s Degree Programme with Columbia University since 2016 . They include Mr. Chen Bowen, who was recently awarded two prestigious scholarships (the William Strong Scholarship Fund and the Richard Stockton and Frances Rojack Scholarship).

Laser Molecular Beam Eptaxy (L-MBE) System with a Connected E-Beam Evaporator.

The department has succeeded in acquiring major external funding support. For example, Prof. Wang Xunli received a Collaborative Research Fund grant from Hong Kong’s Research Grants Council and Prof. Bao Wei and Dr. Liu Qi each received significant funding from China’s Ministry of Science and Technology.

This Dilution Refrigerator, equipped with a 12 Tesla magnet, is capable of reaching 20 millikelvin.

Prof. Wang Xunli and Dr. Liu Qi received The President’s Award 2021 from CityU.

Physical Property Measurement System (PPMS).

Dr. Ma Junzhang became the first person ever to observe fastmoving excitons in metal, unlocking the potential to speed up digital communications.

A research team co-led by Prof. Wang Xunli achieved a break through in the quest to solve the structural mystery of glass.

11 | City University of Hong Kong

Building a Future with “Econophysics”

Unlike many organisations, CityU Physics pays more than lip service to its mission statement. The success of recent graduates, like Nate Yeung Kin-ho, is proof that the department’s commitment to providing rigorous training and preparing students for competitive job opportunities or advanced studies, is real rather than theoretical.

Nate’s decision to study Applied Physics at CityU was driven by a passion for the subject. However, it has also paid off handsomely, opening the door to a rewarding career in one of Asia’s biggest industries – investment banking.

Although engineering might seem a more obvious employment prospect, physics is actually quite closely related to finance. Applying its models and theories to pinpoint economic patterns and predict outcomes is a popular trend. In fact, Nate’s undergraduate dissertation on “econophysics” deals with the application of theories and methods originally developed by physicists to address current economic challenges.

“Today, investment banks recruit across many disciplines. But they usually only consider graduates in quantitative STEM-based

subjects. Physics graduates definitely have a competitive advantage,” Nate explains.

He is complimentary about the department’s comprehensive curriculum, which covers all the essentials – from lectures, tutorials and lab work to Newton’s laws and quantum mechanics. In addition to honing an ability to think logically, Nate is convinced his years at CityU Physics helped him build the strong mathematical abilities and programming skills which are in extremely high demand in the dynamic world of financial services.

“The decision to join the investment banking industry reflects a perfect balance between my skill set and personal interests. Everything I learned in physics has proven very useful – especially the analytical approach and a robust quantitative and coding background. They have been crucially important in demonstrating my abilities and building a career in the industry,” he says.

“The decision to join the investment banking industry reflects a perfect balance between my skill set and personal interests.”

Nate Yeung Kin-ho FX Trader, Deutsche Bank CityU Physics Alumnus

Her Dream Job is Saving Lives

Dr. Monica Kan Wai-kwan Senior Physicist and Department Manager Department of Clinical Oncology, Prince of Wales Hospital

CityU Physics Alumna

The editors of Physical Review Letters recently remarked that today physics research is increasingly about interweaving different areas – physics with chemistry, materials science and even biology. While the observation is valid, it doesn’t surprise Dr. Monica Kan Wai-kwan, whose entire career has been defined by a mix of disciplines.

As an alumna of CityU Physics, her aspiration to become a medical physicist began as an undergraduate. However, since the key qualification, a master’s degree in

Dr. Kan accepted. After pursuing a doctorate at CityU from 2010 to 2015, her career took off. She now works as the Senior Physicist and Department Manager, in the Department of Clinical Oncology at the

Her interdisciplinary knowledge is invaluable in ensuring that equipment and radiation sources are safe for patients and medical staff. She is closely involved in radiotherapy and radiological diagnostic procedures.

“Technology changes so rapidly that keeping abreast of it is a great challenge. Whenever we have new equipment, we need to perform quality assurance tests and solve any technical problems, so it can be put into service as quickly, safely and smoothly as possible,” says Dr. Kan.

Although her job is demanding, it is also hugely rewarding. “I learn new knowledge all the time and apply it to improve patient services. That’s how I get pleasure from work,” she says.

That changed when a CityU professor, who remembered her passion for medical physics, phoned out of the blue with an invitation to take part in a collaboration between CityU and a hospital. Even better, the resulting research project would count towards her master’s degree.

City University of Hong Kong

“I learn new knowledge all the time and apply it to improve patient services.

That’s how I get pleasure from work.”

International Recognition

CityU Physics was founded on the vision of becoming “a leading physics department in the Asia-Pacific region.” With state-of-the-art facilities and a world-class faculty, it is more than meeting that aspiration. The department has earned an enviable international reputation and won numerous awards for academic excellence and cutting-edge research. The bright and energetic student body has also made its mark on the awards front.

Faculty Winners Award Organisation Year

Dr. Denver Li Danfeng Innovators Under 35 China

MIT Technology Review 2022

Prof. Wang Xunli The President’s Awards 2021 City University of Hong Kong 2022

Dr. Liu Qi The President’s Awards 2021 City University of Hong Kong 2022

Prof. Chu Sai-tak Best Paper for 2019 Journal of Lightwave Technology 2022

Prof. Paul Chu Kim-ho Highly Cited Researchers 2017, 2018, 2019, 2020, 2021 Clarivate Analytics 2017 - 2021

Prof. Chu Sai-tak Ranked No.1 in Nature Communications’ Top 50 most downloaded physics articles published in 2020 Nature Communications 2021

Prof. Wang Xunli Croucher Senior Research Fellowship 2021 Croucher Foundation 2020

Prof. Wang Xunli Fellow Neutron Scattering Society of America 2020

Dr. Sunny Wang Xin Outstanding Supervisor Award 2019 City University of Hong Kong 2020

Dr. Sunny Wang Xin The President’s Awards 2018 City University of Hong Kong 2019

Prof. Zhang Ruiqin Fellow American Physical Society 2018

Student Winners Study Programme Award Organisation Year

Chen Bowen

Joint Bachelor’s Degree Programme with Columbia University Awardee Richard Stockton and Frances Rojack Scholarship 2022/23

Chen Bowen, Qiu Siyuan and Li Hengzhi

Chen Bowen

Wang Guomin

Naeem Muhammad

Shahmohammadi Beni Mehrdad

Wu Peilin

Joint Bachelor’s Degree Programme with Columbia University (Chen and Qiu); BSc Applied Physics (Li)

Winner Hong Kong Preliminary of the PLANCKS competition 2022

Joint Bachelor’s Degree Programme with Columbia University Awardee William Strong Scholarship Fund 2021/22

2018 PhD Physics graduate; now Postdoc at CityU Physics Awardee RGC Postdoctoral Fellowship Scheme 2021/22

2020 PhD Physics graduate First Prize (Postgraduate group) Best Paper on Materials 2020

Columbia University, School of General Studies 2022

Physical Society of Hong Kong 2022

Columbia University, School of General Studies 2021

University Grants Committee 2021

Materials Division of the Hong Kong Institution of Engineers 2021

2020 PhD Physics graduate Outstanding Research Thesis Award 2020 Chow Yei Ching School of Graduate Studies, City University of Hong Kong 2020

2019 BScAP graduate College of Science Medal 2019

Kong Yuk-kei 2020 BScAP graduate

Mentor Service Award 2017/18

Wong San-kui 2022 BScAP graduate 2nd Runner-up Bank of China HK FinTech Hackathon 2018

College of Science, City University of Hong Kong 2019

College of Science and Engineering, City University of Hong Kong 2018

Bank of China (Hong Kong) 2018

Elite Scholars

Fellowships are the gold medals of academic life. Valued by individuals and institutions alike, they reward outstanding achievements and recognise a scholar’s professional reputation. Many of our alumni are continuing their learning journeys after winning prized local and international fellowships for their commitment to academic excellence.

Hong Kong PhD Fellows

They include Jung Junho, whose academic qualifications continue to grow. In addition to becoming a Hong Kong PhD Fellowship Scheme (HKPFS) Awardee in 2021/22, he is also the proud holder of a BSc in Applied Physics from CityU.

the more I learned about optical vortices, the more interesting it became. It was the natural choice for my PhD studies at CityU.

The Overseas Internship Scheme (OIS) also offers exciting research opportunities outside of Hong Kong during the summer months. Unfortunately, my plan to work at the RIKEN scientific research institute in Japan was cancelled due to COVID-19. However, there are many other countries, such as France, Canada, or the UK, that accept applications.

learning tai-chi sword as part of a PE course. In my leisure time I often use the piano room, and I joined an electric guitar course organised by students, where I learned how to play and met lots of good friends. I think CityU offers the best of both the academic and personal worlds.”

Jung Junho

HKPFS Awardee (2021/22)

The CityU Physics Experience

“CityU Physics offers numerous valuable programmes, such as the research attachment scheme, which offers the chance to explore specific areas of research. In my case, that was optics, and the experience was instrumental in helping me choose a topic for my undergraduate dissertation. In fact,

CityU is an excellent environment in which to live and learn. For example, the library is accessible and comfortable, and there are plenty of meeting rooms for discussions or group study sessions. The canteens also offer good food at reasonable prices.

Looking beyond the classroom, CityU offers plenty of outlets for other kinds of learning and development, such as sports or music. I’m not much of a sportsman, but I enjoyed

offers the best of both the academic and personal worlds.”

CityU Physics BSc graduate and PhD candidate

“I think CityU

International Fellows

Members of the CityU Physics faculty have joined the fellowship rosters of top international professional societies. Many work alongside other elite scholars with a shared passion for making a difference in the way we live and thrive.

For example, the internationally respected American Physical Society (APS) is committed to advancing the knowledge of physics through outstanding research, scientific meetings, outreach and advocacy. Its fellowship roll now includes an increasing number of members from CityU Physics, including:

Paul K Chu [2008]

Wang Xunli [2010]

[2017]

For seminal contributions to the understanding of plasma – materials interactions as well as development and applications of innovative plasmabased surface modification and materials synthesis technologies and

For sustained contribution in neutron diffraction studies of structure, phase transformations, and mechanical behavior in materials and engineering systems and leadership in the design and construction of a versatile engineering diffractometer at the Spallation Neutron

For pioneering work and contributions in multi-photon interference, quantum entanglement of continuous variables, generation of narrow-band two-photon sources of light, for the work on precision phase measurement in quantum metrology, and work on

Bao Wei [2012]

For neutron scattering studies of the magnetic structure and spin dynamics of highly correlated electron

For path-breaking contributions to the development of quantummechanical many-body methods as well as modeling and simulation of large electronic systems, such as those with nanosurfaces, promoting their applications in the fields of environment, energy, biology and medicine.

Jeff Ou Zheyu

Zhang Ruiqin [2018]

Learning for a Successful Life

In line with CityU’s goal of preparing each new generation to face the future, the BSc Physics programme is tailored to develop logical thinking and problem-solving skills that benefit students throughout their entire lives.

state physics, optics, medical physics, financial engineering and our newest offering, soft matter physics. Following the explosion of interest in A.I. among academics and industry players, new modules on the application of machine learning have been added to the computational physics course. Undergraduates now have the opportunity to pursue A.I.-related research projects, building valuable knowledge in a fastchanging field.

Encouraging Excellence

Effective learning requires a supportive environment. The CityU Physics programme begins by assigning each new student a faculty member as a personal academic advisor. They are also paired with a senioryear peer, whose experience can help them navigate the ins and outs of university life.

provides a solid foundation in fundamental physics, which enables students to explore

Such comprehensive support leaves CityU Physics graduates well positioned to embark on further studies, or pursue rewarding professional careers in a wide range of sectors, from scientific research and technological development to medical physics, data science, finance or STEM

Students with an intense interest in scientific research, are encouraged to participate in the Undergraduate Research Attachment Scheme. It offers an opportunity to join a professor’s team and gain first-hand experience in the challenges of day-today research work. Undergraduates can broaden their educational and cultural horizons through the Outbound Student Exchange Programme, which is packed with opportunities to study at partner universities overseas.

Students are also encouraged to join the department’s outreach activities, such as Information Days, to develop useful interpersonal skills and increase their understanding and connections with the community.

| City University of Hong Kong

Doubling Down

CityU offers a variety of programmes to help elite students develop their talents. For example, undergraduates who demonstrate excellent academic performance in their first two years of study can apply to the Joint Bachelor’s Degree Programme between CityU and Columbia University in New York. Successful candidates spend their third and fourth years studying in the United States, earning a BSc from CityU and a BA from Columbia University.

Wu Peilin is one of nearly a dozen students who have participated in the programme. After earning his BSc and BA, he continued his studies with an MSc in Theoretical Physics at King’s College London.

“Studying in the Joint Bachelor’s Degree Programme was an extremely rewarding journey… both academically and personally. The biggest lesson that I’ve learned [was the] personal paradigm shift after the expansion of my horizon. Every conversation with a great mind around the campus turned out to be inspiring. Even though a two-year study [at Columbia] might be a bit short in time, it was well enough to peek through the cultural, social, political and religious differences, and those discrepancies really lifted me out of the normal plane of comprehension in a local perspective and granted me a glimpse of the whole picture.”

Next Level Learning

The most challenging addition to the CityU Physics talent development portfolio is the recently launched the Undergraduate plus Taught Postgraduate Degree Programme. Designed to nurture students through integrated learning, this initiative offers opportunities to access courses that are normally only taught at the postgraduate level, and participate in advanced research projects. After fulfilling the programme requirements, successful candidates receive two degrees – a BSc in Physics and an MSc in Applied Physics.

WU Peilin – BSc, BA, MSc

Diversity, Opportunity and Excellence

Since its launch in 2020, the CityU Master of Science in Applied Physics Programme has gained a worldwide reputation. The volume of applications has more than doubled, with candidates coming from the USA, Canada, the UK, Germany, mainland China as well as Hong Kong. A high proportion obtained their bachelor’s degrees from prestigious international schools, including the University of Toronto, the University of Edinburgh, as well as Nanjing University, Zhejiang University, the University of Science and Technology of China, Hong Kong Polytechnic University and CityU.

The background of students is equally diverse, covering physics, chemistry, materials science, mechanical engineering, bioengineering, and computer science. However, as their personal statements show clearly, they all share a common desire and intense commitment to succeed academically and professionally.

The fast-growing MSc Programme is constantly adding new opportunities that appeal to high-quality applicants. It now offers courses in three sub-fields: Biomedical Physics, Energy Materials Physics, and General Advanced Physics. They equip students with highly marketable professional skills which are in demand in emerging industries like renewable energy vehicles, and in interdisciplinary positions, such as medical tech specialists.

The faculty is involved in a broad range of advanced research projects, tailored to develop and challenge MSc students. This valuable experience prepares them for a smooth transition to future PhD studies, as well as teaching them to think critically and solve problems.

“Throughout the MSc Programme, I enjoyed exploring cutting-edge research alongside faculty members and combining relevant experimental techniques with theory. The knowledge gained from the programme enabled me to successfully apply for and receive a PhD scholarship to continue my research journey.”

Ding Xiaoqi – CityU Physics MSc graduate and PhD candidate

Reshaping Science

The CityU Physics PhD programme has developed rapidly. Much of this success is due to a talented faculty made up of young, rising stars. Working at the forefront of the discipline, they are producing remarkable fundamental research which is reshaping our understanding of core scientific principles.

This internationally recognised faculty now includes 6 Chair Professors, 4 Professors, 4 Associate Professors, and 12 Assistant Professors. They are focused on five main research areas.

• Theoretical and Computational Physics

• Spectroscopy and Imaging

• Atomic, Molecular and Optical Physics

• Quantum Materials

• Soft Matter and Biophysics

Cutting-edge research is a critical part of our PhD programme. It includes “hot” topics, such as topological insulators, Dirac and Weyl semimetals, superconductivity, neutron scattering, quantum computation and information, machine learning, artificial structures and 2D materials, and molecular machines.

The department has always produced outstanding research. It is also making waves in the media. Its research is published regularly in high-profile academic journals, such as Nature, Science, Physical Review Letters, Nature Materials, and Nature Communications. CityU Physics’ insights also receive broad coverage in influential online publications, including EurekAlert!, Phys.org, and Science Daily, and are reported in CityU research stories.

A Perfect Research Platform

Our advanced curriculum attracts some of the world’s brightest PhD students. Revamped in 2019, it now comprises six core courses, including Advanced Solid State Physics, Advanced Quantum Mechanics, Advanced Electrodynamics, Advanced Computational Methods, Statistical Mechanics, and Modern Characterisation Techniques for Materials Physics. The addition of two new courses – Introduction to Quantum Optics and Introduction to

Biophysics – has extended the Department’s research even further.

Combined with other research methodology and ethics courses as well as electives, the curriculum offers PhD candidates the perfect platform for theoretical and/ or experimental research. Many of our PhD students received their bachelor/ master’s degrees from the world’s top academic institutions, such as Brown University, The University of California, Davis, The University of Manchester, and

Peking University. The programme has also attracted international students from Korea, Vietnam and Malaysia.

In 2021-2022 the Department welcomed 22 new PhD students, including three Hong Kong PhD Fellowship Awardees. With the addition of several energetic new faculty members from the United States and Europe, we expect the number of PhD admissions to increase significantly in the coming years.

Formula for Success

As well as encouraging academic development, the CityU Physics PhD programme provides a solid foundation for career success.

Dr. Wei Xiaoya, a graduate supervised by Prof. Wang Xunli, is now a Research Scientist at the newly established Institute of Advanced Science Facilities in Shenzhen. She is responsible for the entire life cycle planning, construction, operation and maintenance of its integrated particle facilities.

Supervised by Dr. Sunny Wang Xin, CityU PhD graduate Dr. Zhang Xiaoming was awarded the prestigious Boya Postdoctoral Fellowship by Peking University.

Looking beyond academia, Dr. Li Junning, another 2021 graduate supervised by Dr. Wang, now works as a Quantum Algorithm Engineer at Huawei Technologies Co., Ltd. CityU Physics looks forward to seeing more graduates enjoying equally exciting industry careers.

Dr. Peng Jie, a recent PhD graduate supervised by Dr. Wang Shubo, has been recruited by PricewaterhouseCoopers and will soon start her career.

Dr. Li Junning

21 | City University of Hong Kong

Dr. Zhang Xiaoming

Funding the Future

The Department is dedicated to encouraging excellence in unique, paradigmshifting research. This commitment has helped our academic staff earn prestigious honours across many subspecialties and attract major research grants.

During the last two years the department has achieved outstanding results in regular funding exercises, such as the Research Grants Council’s Early Career Scheme (ECS) and the General Research Fund (GRF), in addition to the grants offered by the University.

Grants Recipients

ECS Dr. Chai Yu, Dr. Denver Li Danfeng, Dr. Li Haixing and Dr. Zhang Zhedong

GRF Dr. Dai Liang, Dr. Hoi Io-chun, Dr. Denver Li Danfeng, Dr. Li Xiao, Dr. Liu Qi, Prof. Jeff Ou Zheyu, Prof. Wang Xunli, Dr. Yu Wing-chi and Prof. Zhang Ruiqin

CityU Physics has also been highly successful in competing for external grants. They include those from the Hong Kong Government, the Chinese Central Government and private foundations.

Grants Recipients Value Provider Year

Croucher Senior Research Fellowship

Prof. Wang Xunli HK$ 2 million Croucher Foundation 2021

Collaborative Research Fund (CRF) HK$ 4.7 million Research Grants Council 2021

National Key Technologies R & D Programme Prof. Bao Wei RMB 3.67 million Ministry of Science and Technology of China 2020

National Key Technologies R & D Programme Dr. Liu Qi RMB 1.9 million Ministry of Science and Technology of China 2020

K. C. Wong Education Foundation Conference Sponsorship Programme

Dr. Li Xiao HK$ 48,000 K. C. Wong Education Foundation 2021

General Research Grant Dr. Denver Li Danfeng RMB 610,000

Innovation and Technology Fund Dr. Condon Lau HK$ 602,025

National Natural Science Foundation of China (NSFC) 2021

Innovation and Technology Commission 2021

Innovation and Technology Fund Prof. Paul Chu Kim-ho HK$ 1.6 million Innovation and Technology Commission 2021

Innovation in Action

As scientific disciplines become increasingly interconnected, CityU Physics is playing a major role in expanding the understanding of underlying principles. The department’s research teams are also exploring the practical ways in which this new knowledge can be applied to improve the quality and sustainability of modern life.

First Observation of Fast-moving Excitons in Metal could Accelerate Digital Communications

In a world first, a team co-led by a physicist at CityU has discovered that excitons –excited electrons bound to empty electron “holes” – can exist stably and travel rapidly through metal. Because excitons can be generated by energy from light and have no electrical charge, this discovery makes them a potential, higher-speed alternative to free electrons as carriers of digital information.

The work was co-headed by CityU Physics Assistant Professor, Dr. Ma Junzhang. It not only provides a roadmap for the further study of excitons, especially in metals, but also demonstrates their potential application as high-speed information carriers in future conductor devices.

“Our work now paves the way to generating high-velocity but tunable mobile excitons in metals. This new direction will advance R&D in computing and communication devices that transmit optoelectronic information,” said Dr. Ma.

Sound vortex generation enabled by spin-orbit interaction in real space.∆2

CityU Physicists Discover Special Transverse Sound Wave

A research team at CityU has discovered a new type of sound wave that travels through air and fluids in the same way as light. The sound waves vibrate transversely carrying full vector properties of both spin and orbital angular momentum. In addition to shattering previous scientific beliefs, the findings open a path to the development of novel applications in acoustic communications, and acoustic sensing and imaging.

The research was initiated and co-led by CityU Physics Assistant Professor, Dr. Wang Shubo. It offers new perspectives and functionalities for developing novel applications in acoustic communications, acoustic sensing and imaging.

“This is just a precursor. We anticipate more explorations of the intriguing properties of transverse sound. In future, by manipulating these extra vector properties, scientists may be able to encode more data into the transverse sound to break the bottleneck of traditional acoustic communication faced by normal sound waves,” said Dr. Wang.

∆ [1]

[2]

23 | City University of Hong Kong

This illustration depicts different exciton subtypes identified in metallic TaSe3

Dr. Ma Junzhang who, together with his talented collaborators, discovered the existence of robust mobile excitons in metals.

Ma, J., Nie, S., Gui, X. et al. Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3 . Nature Materials 21, 423–429 (2022).

Wang, S., Zhang, G., Wang, X. et al. Spin-orbit interactions of transverse sound. Nature Communications 12, 6125 (2021).

Hunting Down the First Unpaired Weyl Magnetic Monopoles

Similar to a magnet that always has both north and south poles, special quasiparticles in condensed matter known as “Weyl Fermions” were always predicted to appear in pairs with opposite chirality (i.e., as mirror images of each other). However, there was no experimental evidence that unpaired Weyl points existed in condensed matter until recently, when a CityU physicist observed the first unpaired singular Weyl magnetic monopoles in a specific kind of single crystalline solid.

new insight into the fundamental physics of Weyl magnetic monopoles in condensed matter. The special properties of the monopoles, such as high electronic mobility, their response to an outside magnetic field and low heat rate, also make them good candidates for future spintronic devices, such as quantum and neuromorphic computers.

Breakthrough in the Structure of Glass

Glass is one of the most common everyday materials. Yet the detailed structure of this non-metallic and non-liquid material has always been a major mystery for science.

A research team co-led by Chair Professor and Head of CityU Physics, Prof. Wang Xunli, discovered that amorphous (non-crystalline) and crystalline metallic materials share the same structural building blocks. It is the connectivity between these blocks that distinguishes the crystalline and amorphous states of the material.

“Our experimental study shed light on the structure of amorphous materials at extended length scales. This will go a long way towards aiding our efforts to figure out the structure of glass,” said Prof. Wang.

The research work was co-led by CityU Physics Assistant Professor, Dr. Ma Junzhang, who believes the discovery could provide

The researchers believe that this understanding is vital to the design of new materials, because it is the structure that determines their properties.

∆

[3 ] Ma, JZ., Wu, QS., Song, M. et al. Observation of a singular Weyl point surrounded by charged nodal walls in PtGa. Nature Communications 12, 3994 (2021).

[4] Lan, S., Zhu, L., Wu, Z. et al. A medium-range structure motif linking amorphous and crystalline states. Nature Materials 20, 1347–1352 (2021).

The research team identified 37 Weyl points in the momentum space within a sample of PtGa.∆3

Prof. Wang Xunli’s research team uses synchrotron and in-house X-ray instruments to examine specimens.∆4

∆

New Chips Accelerate Data Transmission

CityU Physics has played a pivotal role in advancing data transmission speeds on the internet. According to the research team, the breakthrough could enable users to download a thousand high-definition movies in less than a second.

This exciting discovery will help to address the world’s insatiable appetite for faster internet connectivity. The demand has become even more acute following the COVID-19 outbreak, which has led to large numbers of people working from home and using technology for socialising and entertainment.

The core of this technological advance is a novel chip developed by CityU Physics Professor Prof. Chu Sai-tak. The innovation demonstrates the capacity of micro-combs – optical frequency responses based on micro-ring resonators, or MRRs – to perform ultra-high speed optical data transmission. As single, compact integrated chips that can support any wavelengths, MRRs could replace many of the parallel lasers that are currently used.

“Soliton crystals within the micro-ring resonators are high in intrinsic stability and easy to generate, and are thus highly suitable for demanding applications such as ultra-dense coherent optical communication,” said Prof. Chu.

multiple impurity systems, such as hightemperature superconductors.

Dr. Ivan Valerievich Borzenets, a former CityU Physics Assistant Professor and currently an Adjunct Professor with the department, collaborated with scientists from Germany, Japan and Korea on this breakthrough. Their next step is to investigate different ways to control the Kondo state.

“Many other manipulations can be done on the device. For example, we can use two impurities at the same time and see how they will react when the clouds overlap. We hope the findings can provide insights into the understanding of multiple impurity systems such as Kondo lattices, spin glasses, and high transition-temperature superconductors,” said Dr. Borzenets.

First Ever Experimental Observation of the Kondo Cloud

Physicists have been trying to observe the Kondo cloud quantum phenomenon for decades. An international research team that included a scientist from CityU, recently developed a novel device to successfully measure the length of the Kondo cloud, and even allow it to be controlled. The findings represent a milestone in condensed matter physics and could provide insights for understanding

[5] Corcoran, B., Tan, M., Xu, X. et al. Ultra-dense optical data transmission over standard fibre with a single chip source. Nature Communications 11, 2568 (2020).

[6] V. Borzenets, I., Shim, J., Chen, J.C.H. et al. Observation of the Kondo screening cloud. Nature 579, 210–213 (2020).

25 | City University of Hong Kong

Dr. Borzenets stands next to a dilution refrigerator –an essential item of equipment for observing Kondo clouds at low temperatures – in the CityU laboratory.∆6

Prof. Chu Sai-tak works on the design and fabrication of the chips which could enable the world’s fastest internet speeds.∆5

Research makes CityU Physics a Leader in Hong Kong

In a Research Assessment Exercise (RAE2020), commissioned by Hong Kong’s University Grants Council, an independent international panel rated 38% of CityU Physics’ research output as four-star, which is regarded as “world-leading.” This rating puts the department in the top spot in Hong Kong.

Principal Investigator Prof. Bao Wei

Using the unique power of neutron scattering in probing microscopic processes in materials, Prof. Bao Wei has investigated the interplay between superconductivity and magnetism in new superconductor systems. Doping effects and phase diagrams have been established for Ba(Fe0.92-xCo0.08Vx)2As2 [1], a quantum scaling in Sr2CuTe1-xWxO6 [2], and antiferromagnetic structure and magnetic properties in Dy2O2Te [3]. He has also been involved in the design and construction of the state-of-art instruments at neutron user facilities.

[1] J. Sheng et al., Phys. Rev. B 101, 174516 (2020).

[2] W. Hong et al., Phys. Rev. Lett. 126, 037201 (2021).

[3] J. Liu et al., Phys. Rev. B 105, 134419 (2022).

Principal

Investigator

Dr. Chai Yu

Soft Matter Group

Over the past year, the Soft Matter Group has continued to work on exploring various soft matter systems and understanding their unique behaviours at different interfaces. With the help of advanced in situ atomic force microscopy, the group successfully achieved direct imaging of the attachment of charged nanoparticles to a liquid interface, where the adsorption dynamics and interfacial jamming effect were revealed in unprecedented detail [1]. Inspired by the interfacial jamming, the Soft Matter Group proposed a magneto-responsive and reconfigurable interfacial self-assembly process, i.e. MRRIS, to lock ferrofluids in the absence of an external magnetic field. These new ferrofluids have both liquid characteristics, such as self-healing, and solid characteristics, like mechanical integrity. The discovery provides opportunities for the fabrication of all-liquid devices [2] .

[1] Y. Chai et al., Sci. Adv. 6, eabb8675 (2020).

[2] S. Zhao et al., Nano Lett. 22, 5538-5543 (2022).

The design simulation of an XYZ magnet for manipulating the neutron spin orientation.

A laser-pumped He-3 neutron spin polarizer.

The cover of this issue of Science Advances illustrates the attachment of single charged nanoparticles to the water-oil interface.

Structuring a ferrofluid droplet through the MRRIS process using an external magnetic field.

Principal Investigator

Prof. Chu Sai-tak

The aim of Prof. Chu Sai-tak’s research is to develop integrated optical devices for novel applications in linear, nonlinear and quantum optics. Over the past two decades, integrated optical devices have been used in a wide range of applications, including optical communications, sensing, metrology, RF and microwave photonics, and more recently in quantum optics.

[1] M. Rowley et. al., Nature 608, 303–309 (2022).

[2] T. Sun et al., Nat. Commun. 13, 1032 (2022).

[3] X. Xu et al., Nature 589, 44-51 (2021).

Principal Investigator Dr. Dai Liang Computational Soft Matter and Biophysics Group

In the last two years, Dr. Dai Liang and the Computational Soft Matter and Biophysics Group have measured and explained the deformations of DNA and RNA induced by ions, stretching force, temperature changes, and methylation. They also developed one simple and unified physical model to quantitatively explain many deformations. Furthermore, Dr. Dai and the group have elaborated the impacts of these DNA/RNA deformations on DNA packaging, DNA/RNA-protein interactions, and gene expression. Considering the unique capabilities of the DNA double-helix, his team also designed artificial double-helix structures through the selfassembly of simple polymer models using computational methods.

[1] C. Zhang et al., Sci. Adv. 8, eabn1384 (2022).

[2] J. Du et al., Phys. Rev. Lett. 128, 197801 (2022).

[3] X. Qiang et al., Phys. Rev. Lett. 128, 108103 (2022).

DNA twist change with salt and the underlying mechanism.

Microring resonator assisted multiphoton emission with core-shell nanoparticles allowing the conversion of low-energy photons at 1550 nm to high-energy ultraviolet photons at 380 nm.

Principal Investigator Dr. Condon Lau

Dr. Condon Lau develops imaging and spectroscopy methods for biomedical applications. Recent examples include a high spatial resolution resting-state functional magnetic resonance imaging method to study the rodent brain. This was used to explore the effects of environmental enrichment on brain functional connectivity at different stages of the circadian cycle. He recently developed some novel sample preparation methods for laser induced breakdown spectroscopy that improve detection limits and signal-to-noise ratios. These were applied to understand the impact of lithium exposure on the brain and perform depth-wise chemical analysis.

[1] Y. Liu et al., ACS Sens. 7, 1381-1389 (2022).

[2] F. Manno et al., NeuroImage 252, 119016 (2022).

[3] I. Ahmed et al., Bipolar Disorders. 23, 615-625 (2021).

Principal Investigator

Dr. Denver Li Danfeng

Oxide Quantum Materials Group

Headed by Dr. Denver Li Danfeng, the Oxide Quantum Materials Group is broadly interested in oxide quantum materials and heterostructures, with a significant focus on the synthesis of novel complex oxide materials, oxide interface physics, lowdimensional superconductivity, 2D oxide nanomembranes, and quantum materials by design. Recent research progress has mainly been in elucidating intrinsic magnetism and its possible relationship with superconductivity in infinite-layer thin-film nickelate [1], as well as developing a water-soluble template for ex situ synthesis of freestanding superconducting SrTiO3 nanomembranes [2] .

[1] J. Fowlie et al., Nat. Phys. 18, 1043-1047 (2022).

[2] D. Li et al., Nano Lett. 21, 4454-4460 (2021).

(a) Schematic diagram of the depth profiling process by the scabbarded NE-Ag needle sensor.

(b) Schematic diagram of the LIBS setup and LIBS line scan.

(c, d) Ablation spots by LIBS line scan on the NE-Ag needle at different magnifications.

Stabilisation of Sr3Al2O6 growth templates for ex situ synthesis of freestanding superconducting SrTiO3 nanomembranes.

Principal Investigator Dr. Li Haixing

Single Molecule Electronics Group

Dr. Li Haixing’s lab examines molecules and bio-inspired architectures at the single molecule level to spark advances in electronics, health, and sustainability. Specifically, her lab creates single molecule circuits to probe charge transport processes at metal-molecule-metal junctions, while focusing on uncovering the underlying physics and chemistry that dictate these nanoscale transport phenomena. By applying approaches centred around single molecule techniques onto a variety of synthetic and biological molecules, the lab aims to understand the structurefunction relationships of molecular materials, and ultimately design and create novel functionalities that harness molecular properties.

[1] H. Li et al., J. Am. Chem. Soc. 140, 15080-15088 (2018).

[2] M. H. Garner et al., Nature 558, 415-419 (2018).

[3] H. Li et al., J. Am. Chem. Soc. 139, 10212-10215 (2017).

Principal Investigator

Dr. Li Xiao

Condensed Matter Theory Group

The Condensed Matter Theory Group led by Dr. Li Xiao, focuses on the theoretical study of novel electronic and dynamical properties in condensed matter systems. One of the main research directions is novel dynamical phases of matter in non-equilibrium systems. Recently it studied many-body localisation for interacting onedimensional lattice fermions in random (Anderson) and quasiperiodic (Aubry-Andre) models, focusing on the role of interaction range [1] In other projects it has explored the stability of quantum manybody scar states against random disorders in a 2D PXP model [2] and examined the electronic properties of 2D materials. The group recently collaborated with Prof. McEuen’s group at Cornell University and observed unusual optical selection rules in bilayer graphene in the quantum Hall regime, which can be attributed to many-body interactions present in the high-quality graphene sample [3] .

[1] D. Vu et al., Phys. Rev. Lett. 128, 146601 (2022).

[2] K. Huang et al., Phys. Rev. B 104, 214305 (2021).

[3] L. Ju et al., Nat. Commun. 11, 2941 (2020).

The Journal of the American Chemical Society (JACS) featured the “Mechanism for Si-Si Bond Rupture in Single Molecule Junctions” on its front cover.

The Journal of the American Chemical Society (JACS) prominently covered “Electric Field Breakdown in Single Molecule Junctions”.

Extrapolated quantum phase diagram from simulations on finite-size lattices of L

Landau level spectroscopy of band-gapped bilayer graphene (BLG).

29 | City University of Hong Kong

Principal Investigator Dr. Liu Qi

Dr. Liu Qi’s group focuses on probing the local structural dynamics of layered cathode materials with in situ pair distribution function techniques. In a recent study, it discovered a single-crystal of Ni-rich LiNi0.83Co0.12Mn0.05O2 cathode material with high specific capacity and excellent cycling stability [1]. Using in situ PDF analysis, the group determined that the high performance of this material benefits from an intermediate monoclinic phase between H1H2 transition and stacking faults within a high-voltage H3 lattice. In other research, the group proposed a Ti/Mg co-doping strategy for a model P2-Na2/3Ni1/3Mn2/3O2 cathode material [2]. In situ PDF investigation revealed that an orthorhombic P2’ phase instead of a typical O2 phase occurs at high voltage, and this P2’ phase suggests an activation of charge compensation for stabilised layered structure in this material.

[1] H. Zhu et al., Nano Lett. 21, 9997-10005 (2021).

[2] H. Zhu et al., Adv. Sci. 9, 2200498 (2022).

Principal Investigator Dr. MA Junzhang ARPES Group

The ARPES Group’s research mainly focuses on the study of quantum materials by direct investigation of the characteristics of electronic structure including Fermi surfaces, energy band, Fermi velocity, energy gap, effective mass, carrier density and so on. The most powerful technique to study electronic structure is the stateof-the-art Angle Resolved Photoemission Spectroscopy (ARPES). In recent years, the group conducted seminal research work, including the discovery of unpaired Weyl points, Weyl nodal walls, mobile excitons and trions in low dimensional metal, as well as topological Dirac surface states in Kagome materials.

[1] Y. Hu, et al., Science Advances 8, eadd2024 (2022).

[2] J.-Z. Ma, et al., Nature Materials 21, 423–429 (2022).

[3] J.-Z. Ma, et al., Nature Communications 12, 3994 (2021).

In situ PDF analysis of local structural dynamics in (A) single-crystal Ni-rich LiNi0.83Co0.12Mn0.05O2 cathode material and (B) P2-Na2/3Ni1/3Mn2/3O2 cathode material.

(a) Observation of unpaired magnetic monopole in momentum space of PtGa.

(b) Mobile excitons and trions in 1D metal proved by ARPES.

(c) Topological Dirac surface states in kagome material GdV6Sn6.

Principal Investigator

Dr. Michon Bastien

Infrared Optical Spectroscopy Group

Using Fourier-Transform infrared spectroscopy to look into quantum materials, such as unconventional superconductors and topological materials, Dr. Michon Bastien and the Infrared Optical Spectroscopy Group recently demonstrated scaling laws in optics on cuprate superconductors compatible with the presence of a quantum critical point [1]. A theoretical model is expressed to simultaneously describe three signatures of quantum criticality in experimental probes: linear temperature resistivity, log(T ) specific heat [2] and scaling laws in optics. This work was submitted to Nature Physics and follows another study on the role of electronic correlations on superconductivity [3]

[1] B. Michon et al., arXiv:2205.04030 (2022) (submitted to Nat. Phys.).

[2] B. Michon et al., Nature 567, 218-222 (2019).

[3] B. Michon et al., Phys. Rev. R 3, 043125 (2021).

Principal Investigator

Prof. Jeff Ou Zheyu

In collaboration with Tianjin University, Prof. Jeff Ou Zheyu has implemented a programmable two-photon source. With a few strokes on a keyboard, it is possible to achieve drastically different spectral properties of photon pairs. The joint spectral functions of the two-photon pairs are shown from left to right: (b1) factorised (b2) correlated (b3) anti-correlated and (b4) three-mode entangled. He also discovered a new way of homodyne detection to recover quantum interference lost due to photon distinguishability. This reveals the wave and particle duality of the photon in one experiment, but with different measurement schemes. In collaboration with East China Normal University, he also implemented a linear interferometer (SU(2)-type) inside a nonlinear interferometer (SU(1,1)-type), as shown below. This is a more practical variation of the newly discovered quantum entangled SU(1,1) interferometer that can be applied in quantum sensing to increase sensitivity beyond the limits of classical waves of light.

[1] L. Cui et al., APL Photonics 5, 0069383 (2022).

[2] N. Hou et al., PRX Quantum 3, 020313 (2022).

[3] W. Du et al., Phys. Rev. Lett. 128, 033601 (2022).

(a) Linear scaling law of the optical scattering rate in agreement with the well known linear temperature resistivity.

(b) The quasiparticle effective mass and the optical effective mass at zero frequency both show a log(T ) dependence.

Two-photon joint spectral function for different engineered states.

Schematic arrangement for a nested SU(1,1) interferometer.

31 | City University of Hong Kong

Principal Investigator

Prof. Ren Yang Energy & Materials Physics Group

Prof. Ren Yang’s research focuses on understanding the fundamentals and potential applications of advanced materials by using stateof-the-art techniques at synchrotron X-ray and neutron scientific facilities along with other tools. Considering the fact that high-flux X-ray beams often cause damage in probed materials, Prof. Ren took his research in a new direction to understand the interaction between synchrotron X-rays and matter, and to exploit its potential application in materials manipulation and discovery. He demonstrated for the first time that synchrotron X-rays can be utilised to synthesise nanoparticles on Cu thin films in the ambient atmosphere. [1] Furthermore, he showed that synchrotron X-rays can induce silver nitrate compounds on Ag thin films in air. The results not only provide new clues about abiotic nitrogen reduction, which was critical to the origin of life on the early Earth, but also present a new strategy for materials synthesis. [2] However, the underlying physics of the new findings remain puzzling and need further investigation.

[1] J. Hui et al., ACS Appl. Mater. Interfaces (2022), DOI: 10.1021/acsami.2c01329.

[2] J. Hui et al., Small (2022), DOI: 10.1002/smll.202202720.

Principal Investigator Dr. Wang Shubo

Dr. Wang Shubo discovered a new type of sound wave: transverse sound. Like light, it carries both spin and orbital angular momentum [1] . The findings have shattered previous scientific beliefs about sound waves, opening an avenue to the development of novel applications in acoustic communications, acoustic sensing and imaging. This work was featured in CityU Research Stories and received broad media coverage, including EurekAlert, Phys.org and Science Daily. Recently, Dr. Wang’s research team has demonstrated a novel method of chiral discriminations using the polarisation singularities of simple metal spheres, which can be applied in the optical sensing of chiral molecules [2] .

[1] S. Wang et al., Nat. Commun. 12, 6125 (2021).

[2] S. Jia et al., Phys. Rev. A 105, 033513 (2022).

A schematic showing synchrotron X-rays induced nanoparticles on a Cu thin film.

Department of Physics | 32

In-situ X-ray diffraction patterns of synchrotron X-ray induced nitrogen fixation with silver nitrate compounds.

Acoustic vortex generated by the transverse sound.

Principal Investigator Dr. Sunny Wang Xin Quantum Theory Group

Dr. Sunny Wang Xin and the Quantum Theory Group study theoretical problems arising from the physical realization of quantum computation. For example, Dr. Wang develops optimized control protocols that mitigate noise in manipulation of quantum bits [1], and applies reinforcement learning techniques to quantum state preparation [2] and quantum parameter estimation [3] .

[1] X.-M. Zhang et al., Phys. Rev. A 103, L040403 (2021).

[2] X.-M. Zhang et al., npj Quantum Inf. 5, 85 (2019).

[3] H. Xu et al., npj Quantum Inf. 5, 82 (2019).

Principal Investigator

Prof. Wang Xunli

Prof. Wang Xunli applies state-of-the-art neutron and synchrotron scattering techniques to study the structure and dynamics of advanced materials. Fundamental knowledge of structure and dynamics – where atoms are and how they move – is essential to understanding the properties of materials. Broad topics of interest include phase transformation, deformation behaviors, and lately phonon dynamics. In addition, he is also involved in several collaboration projects, with experiments carried out by students and postdocs at leading neutron and synchrotron sources worldwide.

[1] S. Lan et al., Nature Mat. 20, 1347–1352 (2021).

[2] M. Naeem et al., Sci. Adv. 6, eaax4002 (2020).

[3] X. Y. Li et al., Phys. Rev. Lett. 124, 225902 (2020).

The error detection and mitigation process in a quantum autoencoder.

Sketch of the procedure for applying reinforcement learning methods.

Stress-strain curve obtained at 15 K for CrMnFeCoNi high entropy alloy, showing high strength and extraordinarily large ductility. In situ neutron diffraction experiments played a pivotal role in elucidating the underlying deformation mechanisms leading to the extraordinary ductility.

Principal Investigator Prof. Yu Kin-man

Prof. Yu Kin-man’s research focus includes defect physics in semiconductors, transparent conductors, amorphous alloy oxides for flexible electronics, wide gap oxides with bipolar conductivities for oxide based transparent PN-junction devices and inorganic halide perovskite nanostructures for optoelectronics applications.

, 43795-43805 (2021). , 024049 (2020).

Schematic diagrams showing the structure of a PM6:Y6 blend-based bulkheterojunction organic solar cell (OSC) utilising the amorphous CdInO transparent conductor and the J-V curves.

Principal Investigator Dr. Yu Wing-chi

As part of a group investigating various quantum critical phenomena in interacting many-body systems, Dr. Yu Wing-chi recently proposed a novel concept which she named the Loschmidt amplitude spectrum [1] It provides insights into an open question in dynamical quantum phase transition (DQPT), including how the system behaves around DQPT. She also applied state-of-the-art machine learning techniques to detect phase transitions in condensed matter systems using (quantum) Monte Carlo samples before equilibrium. A significant speed-up in the computational time can be achieved as compared to conventional methods of phase detection using equilibrium samples [2] .

[1] C. Wong et al., Phys. Rev. B 105, 174307 (2022).

[2] J. Ding et al., SciPost Phys. 13, 057 (2022).

Room-temperature optically pumped red-green-blue whispering-gallery mode lasers based on tunable cesium lead halide perovskites (CsPbX3, X = Cl, Br, I) with microcrystal structures.

Snapshot of spin configurations in the XY model below (left) and above (middle) the transition temperature. Machine output as a function of temperature detects the transition at around TC=0.89 (right).

Loschmidt rate spectra in the quenched one-dimensional quantum Ising model.

Principal Investigator

Prof. Zhang Ruiqin Materials Physics Group

To accelerate the discovery of new molecules and materials, Prof. Zhang Ruiqin and the Materials Physics Group have explored the combination of Density Functional Theory and Machine Learning Methods. He and the team developed novel descriptors for hybrid perovskites and organic ligands in predicting bandgaps and yields. They screened hybrid perovskites appropriate for solar cells by proposing descriptors with Machine Learning. In addition, they constructed volcano plots in cross-coupling catalysis to locate active ligands. The work will help in the discovery of perovskites and ligands of organic catalysis which could solve many energy and pharmaceutical problems.

[1] J. Chen et al., J. Phys. Chem. Lett. 13(2), 520-526 (2022).

[2] J. Chen et al., J. Mater. Chem. A 10, 1402-1413 (2022).

A screening framework implemented for discovering promising photovoltaic materials from double hybrid organic-inorganic perovskites.

Principal Investigator

Dr. Zhang Zhedong

Quantum Nonlinear Spectroscopy & Photonics Group

A new quantum statistical theory for exciton-polariton condensation offers a promising paradigm for quantum light sources. Dr. Zhang Zhedong and the Quantum Nonlinear Spectroscopy & Photonics Group used rigorous mathematics to prove the nonequilibrium fluctuation-dissipation theorem with time-reversal symmetry breaking. Their work has demonstrated a quantum femtosecond Raman spectroscopy (QFRS) using entangled photons, capable of capturing ultrafast electron dynamics within 50fs, beyond the Heisenberg limit for resolutions. These are essential for a comprehensive understanding of molecular relaxation and radiation in a highly non-equilibrium regime.

[1] Z. Zhang et al., Phys. Rev. B Lett. accepted (2022).

[2] Z. Zhang et al., Light: Sci. & Appl. 11, 1-9 (2022).

[3] Z. Zhang et al., Phys. Rev. B 104, 085439 (2021).

Combining the steric and electronic effects into a descriptor to construct volcano plots of reaction yields in cross-coupling catalysis.

(a) Out-of-equilibrium molecular aggregates in an optical cavity, forming polariton condensations. (b) QFRS signal for time-evolving electronic coherence, with entangled photons as probe, where T is the time delay relative to the pump pulse.

35 | City University of Hong Kong

World Class Facilities Powering New Ideas and Innovations

CityU Physics relies on cutting-edge facilities to fulfil its mission of serving as a central resource for physics education and research at the University. It is now a hub for scientific exchange and collaboration that is enabling the latest discoveries and innovations.

CAS-CityU Joint Laboratory on Neutron Scattering Science and Technology

The City University of Hong Kong –Institute of High Energy Physics Joint Laboratory with the Chinese Academy of Sciences (CAS) on Neutron Scattering was officially launched on 27 February, 2019. Distinguished guests included CityU President, Prof. Way Kuo; the Nobel Laureate in Physics, Prof. Yang Chen-ning; the Director of the China Spallation Neutron Source (CSNS) and a Member of the CAS, Prof. Chen Hesheng; and CityU’s Chair Professor of Physics and Head of the CityU Department of Physics, Prof. Wang Xunli.

As the only facility of its kind in Hong Kong, the laboratory has tremendous potential to enhance the city’s role in developing science and technology in the Greater Bay Area. It also works closely with the China Spallation Neutron Source (CSNS) in Dongguan on professional training, research projects and facilities.

Research on neutrons can help scientists study the structure of materials. By measuring the change in energy and the momentum of neutron scattering, scientists can better understand the micro structure and movement patterns of materials. Such research will make significant contributions to the development of medicine, new nuclear energy, nanotechnology, physics, and material science.

The Joint Laboratory has been supported by the CAS and Hong Kong’s Croucher Foundation since 2015, and receives funding support from the Collaborative Research Fund under the Research Grants Council. Prof. Chen and Prof. Wang are both co-Directors of the Joint Laboratory.

First User Instrument Commissioned at the CSNS – Multi Physics Instrument

On 26 January, 2021, the Multi Physics Instrument (MPI) received a neutron beam from the target station, marking the instrument’s successful completion after two years of construction. Built in cooperation with Dongguan University of Technology and City University of Hong Kong, the MPI is the first neutron total scattering instrument in China.

The MPI will mainly be used for research on materials with different ordered structures, focusing on analysis of long-range order and locally disordered materials, and longrange disorder and short-range ordered materials. It will serve users in both the Chinese mainland and Hong Kong, providing an effective tool to probe materials –especially in research on materials science, condensed matter physics, life science and nano-materials.

CityU Centre for Neutron Scattering (CNS)

Due to the close proximity, Hong Kong’s scientific community stands to be a major beneficiary of the CSNS in Dongguan. The Centre for Neutron Scattering (CNS) at CityU was established to allow Hong Kong users and the international neutron scattering community to collaborate with the CSNS. The CNS is a partnership with the CAS-CityU Joint Laboratory on Neutron Scattering Science and Technology and the Guangdong-Hong Kong-Macau Joint Laboratory for Neutron Scattering.

Located in Dongguan, about 70 km north of Hong Kong, the CSNS is a new pulsed neutron source dedicated to neutron scattering research under the Institute of High Energy of the Chinese Academy of Sciences (CAS). The CSNS has been in operation since March 2018 and produced its first neutron beam on the 28th of August.

| City University of Hong Kong

Design and Overview of the Multi Physics Instrument.

Building an Impressive International Reputation

The free exchange of ideas is key to the development of science. Conferences and workshops provide a platform for scholars in different research fields and geographies to communicate and collaborate. They are also ideal opportunities to showcase academic innovation and achievement.

CityU Physics recognised the importance of these interactions from the outset. Our events are designed to put the department on the map as an international centre for discovery and development. Attracting young researchers and prominent scientists alike, they offer students and members of the public a different kind of learning experience compared to traditional classroom courses. The number of attendees from government agencies, investment firms and private enterprises is also constantly increasing.

Accommodating the New Normal

Despite the disruption caused by the pandemic, CityU Physics managed to successfully stage several workshops and symposiums live or online, or in a mix of formats.

CityU’s first major face-to-face event since December 2019 was the 10th International Workshop on Solid-State Quantum Computing, which took place between 29 November and 1 December, 2021. Covering a broad spectrum of solid-state quantum computing topics, it featured three plenary speakers, including Prof. Yasunobu Nakamura and Prof. Franco Nori from RIKEN, Japan, and Prof. Pan Jianwei from the University of Science and Technology of China. Cosponsored by the Croucher Foundation, the event invited a total of 39 speakers from mainland China, Hong Kong, Macau, Taiwan, Japan, Singapore, South Korea, Thailand, Australia, Israel, Sweden, Spain and the United States to discuss their latest findings.

Coming to Terms with Complex Materials

The department hosted the International Conference on Quasielastic Neutron Scattering (QENS) and a workshop on Inelastic Neutron Spectrometers (WINS) between 15 – 20 July, 2018. Focusing on material dynamics under the theme of “New idea, New concept, New design, New instrumentation for New sciences,” QENS-WINS2018 offered an exciting scientific program. With more than 100 presentations at the forefront of the applications of quasielastic and inelastic neutron scattering techniques, the event attracted 120 attendees from 16 countries and regions.

More recently, the department held a threeday International Workshop on Exotic Quantum Effects in Complex Materials from 9 – 11 June, 2022, with plenary presentations delivered by some of the best-known names in the discipline. They included Prof. Girish S. Agarwal from Texas A&M University, who is also a Fellow of The Royal Society, and Prof. Wang Jin from Stony Brook University, who is a respected Member of the European Academy of Sciences. A roster of 28 invited speakers from mainland China, Hong Kong, Sweden, Spain and the United States, also presented their most recent research on emerging quantum effects and other related phenomena in complex materials.

Celebrating Success

The annual Celebration of Physics Symposium is an important part of the young department’s tradition. It provides a platform for students and faculty members to highlight their achievements during the last academic year. A highlight of the most recent “Celebration,” which was held on 1 June, 2022, was the keynote presentation delivered by the world-renowned physicist Marlan Scully, from Texas A&M University in the United States.

Nurturing Young Scholars

Summer courses on fields at the forefront of research play an important role in the career of young scholars. Supported by the Croucher Foundation, the department held the Croucher Summer Course on Neutron Scattering from 9 – 14 July, 2018, focusing on quasielastic and inelastic neutron scattering, while also covering fundamental scattering theories and techniques. This 5-day intensive course featured world-leading neutron scattering scientists and fostered close interaction between students and lecturers.

Continuing to Contribute

As a dedicated member of the academic community, CityU Physics has always recognised its duty to support other

physics-oriented organisations. Many of the department’s staff serve on advisory committees or as board members at a growing number of institutions, including the China Spallation Neutron Source at Dongguan in Guangdong province, the Songshan Lake Materials Laboratory, the Institute of Physics at the Chinese Academy of Sciences in Beijing, and the Physical Society of Hong Kong.

Other academic staff are active members of the Hong Kong Physics Olympiad Committee, the HKDSE Physics Subject Committee of the Hong Kong Examinations and Assessment Authority, and act as panel members for the Research Grants Council. CityU staff also provide editing support for respected international journals, such as the Journal of Applied Physics and the Journal of Environmental Radioactivity

Understanding the Magic of Physics

Exploring the World of Quantum Computing

Conventional computers rely on speed to calculate a staggering number of possibilities. However, the new generation of quantum computers could change the game entirely. By leveraging an understanding of how atomic and subatomic particles interact, they can potentially consider “every possibility” almost instantly, enabling us to solve problems that are currently unsolvable.

from magic.” The technology that is reshaping society certainly looks magical. But the real power behind each new idea isn’t supernatural – it’s physics.

Today some of the most imaginative physics research interweaves different disciplines, combining the experimental with the theoretical and computational, as

well as the quantum with the molecular, soft matter and biophysics. These “Eureka” moments make keeping up with the latest developments a major challenge.

CityU Physics’ Outreach Programme is designed to help the Hong Kong community – from high-school students to executives in local enterprises – understand the potential of new research, and develop their own educational and professional relationships with physics.

In January 2022, Dr. Sunny Wang Xin introduced students at St. Peter’s Secondary School to the essentials of quantum computing in a lecture entitled “The exotic quantum world”. He also served as a panel judge in the “Dream District VR competition” organised by St. Paul’s Secondary School in August 2021.

Dr. Wang also served as a judging panellist in the “Dream District VR competition” organised by St. Paul’s Secondary School.

Dr. Sunny Wang Xin lecturing on quantum computing to students at St. Peter’s Secondary School.

Dr. Liu Qi delivered a popular science lecture on “Lithium-ion Batteries for Portable Electronics” at the YMCA of Hong Kong Christian College in November 2021.

Taking a Hard Look at Soft Matter

Soft materials, which are easily deformed or structurally altered by thermal fluctuations or external forces, offer fascinating possibilities. In December 2021, Dr. Chai Yu addressed an audience of secondary students visiting the CityU campus who were captivated by his lecture on how

In November 2021, Dr. Wang Shubo delivered a popular science talk at the YMCA of Hong Kong Christian College (港青基信書院). The audience of about 15 Form 4, 5 & 6 students was enthralled by Dr. Wang’s introduction to light-induced forces and their application in physics, chemistry, and biology.

Afterwards, the participants joined a short tour of the physics department, examining the state-of-the-art lab instruments, including scanning electron microscopes

Superconductors in Action

Superconductors that minimise energy loss in applications such as electricity transmission cables. They could critical in solving the energy crisis and combatting climate change – either through reducing carbon emissions, or rerouting the power we save to lower-income communities, where it can make a massive difference.

This was one of the topics that Dr. Yu Wing-chi covered in November 2021 during the Science in the Public Service (科學為民) talk series. Her lecture, entitled “Development and Applications of Superconductors,” was delivered at the

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Dr. Yu Wing-chi live-streaming her talk on the “Development and Applications of Superconductors.”

Dr. Chai Yu addressing an audience of secondary students visiting CityU.

Department of Physics

City University of Hong Kong

Phone: (852) 3442-7831

Fax: (852) 3442-0538

Email: phy.go@cityu.edu.hk Website: www.cityu.edu.hk/phy