Promise in Spintronics

Sarah Li joined the University of Utah five years ago as an assistant professor of physics. Her research focuses on using optics to help understand spindependent electronic and magnetic phenomena in semiconductor materials.

“My research is fundamental physics—to study how electron spins behave in materials,” said Li. “The research is called spintronics, short for spin electronics, and we use the electron spin to carry information.” Electrons are basically tiny magnets that orbit the nucleus of an element, and they have their own spin orientation relative to the nucleus. “The spin goes two ways—spin up or spin down,” said Li, “and a spintronic device is expected to process more data with less energy consumption than traditional electronics.” As Li and her team study how to manipulate electron spins in either magnetic materials or semiconductors, they hope to discover new ways to store and process information. Their work has practical applications in developing things like quantum computers, with faster speeds that consume less energy and have greater functionality.

Understanding Perovskites

In the last few years, Li and her team have focused on understanding the spin-dependent properties of a new type of semiconductor, hybrid organicinorganic perovskites, which are crystalized materials with organic molecules in the structure. Perovskites contain excellent semiconductor properties such as high optical absorption and good conductivity, which make them ideal for use in solar cells, LEDs, transistors, sensors, lasers, and other devices. Li and her team are among the first scientists to show the

potential of organic-inorganic hybrid perovskites in spintronics.

Their experiment began with the researchers using chemical precursor solutions to form a hybrid perovskite thin film, which they placed in front of an ultrafast laser capable of shooting short light pulses of 1 over 10 trillion-seconds duration, 80 million times in a second. The laser was then split into two beams: the first beam was aimed at the film to set the electron spinning in a particular direction. The second beam was bent through a series of mirrors, much like a pinball machine, before hitting the perovskite film at increasing intervals to measure how long the electron held its spin orientation.

Applications for Semiconductors

“The results for the hybrid organic-inorganic perovskites were significant,” said Li. “The experiment showed the potential application for them based on spin that was different and distinct from using perovskites for solar cells and LEDs. It was exciting because the hybrid perovskite is truly a promising semiconductor candidate for making spin transistors.”

Born and raised in China, Li became interested in physics at age nine or ten when she happened to read some books that belonged to her cousins. “I couldn’t stop reading—physics opened up a whole new world for me, and I found explanations for many phenomena.” Before high school, Li had limited access to physics textbooks, but by eighth grade, she was studying physics in school.

She attended the University of Science and Technology of China because of its reputation for excellence in research science. “When I began college in the Department of Materials Science and Engineering, my specialty area was materials physics; however, I took many courses in both physics and chemistry.” Before Li entered the university, she planned a five-year program; however, the administration decided to shorten the program to four years. The course work was heavy, with few electives. “My college years were very busy,” said Li. “I received a solid foundation in physics and chemistry, but I didn’t have much of a college or social life.”

She received her Ph.D. from the University of California, Riverside, and was involved with a research group in building machine parts, setups, testing, and debugging. “I really enjoyed my years at Riverside,” said Li. “I learned a lot about building

infrastructure, which helped me in building my own lab at the U. I also enjoyed the freedom I had at Riverside to choose the kind of work I wanted to do.”

When she isn’t in the lab or teaching, Li and her husband and their young son spend time at museums and playgrounds. “I also enjoy crafts and doing things like cooking, sewing, and watercolor painting, but with a young child I don’t have much time for my hobbies. I do make time to hike because it boosts my energy.”

As Li moves forward, she wants her research to continue to be systematic and thorough. Her team’s recent results have opened up new opportunities but also brought up questions, too. “This field of research is still young, and my goal is to develop an understanding of it as completely and deeply as I can. I hope to continue working on spin-device applications that will make a difference.”