Volume 39, Spring 2020
MURJ
MIT Science News in Review
physics
Graphene sheets twisted at ‘magic angle’ electrify physics The Jarillo-Herrero Group explores superconductivity and other exotic properties of twisted bilayer graphene Overlapping sheets of graphene [Credit: National Intitute of Standards and Technology]
Graphene, touted as the wonder the device transformed again into a su- idea was largely dismissed until Jarillomaterial of condensed matter physics, perconductor–an even more shocking Herrero pursued it experimentally in has generated much excitement since discovery. MIT’s Building 13. its discovery in 2004. Now, the JarilTheir crucial insight was that a When the team finally published lo-Herrero Group at MIT launches a single graphene-based device can be in Nature in spring of 2018, their renew wave of graphene enthusiasm by tuned to become an insulator, a su- sults electrified the physics commubringing a literal ‘twist’ into the mate- perconductor, or anything in between. nity. “I haven’t seen this much exciterial. They found that when two sheets “We can explore all those physics in ment in the graphene field since its of graphene are misaligned at a ‘magic one device electrically, rather than initial discovery,” says physicist Chunangle,’ superconductivity and other having to make hundreds of devices. Ning Jeanie Lau in an interview with strange behaviors emerge. It couldn’t get any simpler,” says Pablo Nature. Graphene is the world’s thinnest Jarillo-Herrero, the team’s leader. This work birthed a new field material, a single-atom thick lattice These properties cannot be ob- dubbed “twistronics.” Now, physicists of carbon atoms arranged in a hon- served in perfectly aligned graphene around the world are exploring other eycomb pattern. Although the ex- layers. But when they are rotated rela- twist angles and other 2D materials ceptional strength, thermal besides graphene. Earlier this conductivity, and electrical year, Jarillo-Herrero, MacDonconductivity of graphene are "A single graphene-based device can ald, and Bistritzer received the long established, its intrinprestigious 2020 Wolf Prize in be tuned to become an insulator, sic superconductivity came Physics “for their pioneering a superconductor, or anything in as a surprise. This discovery theoretical and experimental could revolutionize the dework on twisted bilayer grabetween" velopment of high-temperaphene.” ture superconductors, quanWhen asked about his rectum computers, and low-cost energy tive to each other, the graphene su- ognition, Jarillo-Herrero says "I see it solutions. perlattice displays different moiré pat- as an acknowledgement…by the globJarillo-Herrero’s team stacked two terns. Precisely at the magic angle, the al physics community for the work of graphene sheets, twisted them at small electrons in the sheets interact more my fantastic group of graduate stuangles between 0 and 3 degrees, and strongly with each other, giving rise to dents and postdocs, as well as my colthen cooled the device to a fraction of curious physical effects. laborators here at MIT and around the a degree above absolute zero. At the In 2011, Allan MacDonald (UT world.” He also hopes that more young magic angle of 1.1 degrees, the mate- Austin) and Rafi Bistritzer (Applied physicists will explore the beautiful rial acted like an insulator, an unex- Materials-Israel) already predicted the field of 2D materials. pected behavior from the world’s best connection between moiré patterns conductor. When they applied voltage, and electronic properties. But their — Hillary Diane Andales 4
