Sid Parameswaran publishes on unusual new state of matter
5 May 2022
Professor Sid Parameswaran, Tutorial Fellow in Physics, is part of a team which has this week published exciting new research on quantum materials.
Writing in Nature alongside two other members of Oxford’s Rudolf Peierls Centre for Theoretical Physics – DPhil student Yves Kwan and Professor Shivaji Sondhi – Sid and the team report the emergence of an unusual new state of matter in a newly-explored moiré system. This system layers atomically thin two-dimensional crystalline layers with a slight mismatch in their orientation, prompting changes in the speed of electrons moving through the system. Work undertaken at the Massachusetts Institute of Technology in 2018 on superconductivity in a system of twisted graphene prompted a surge of theoretical and experimental activity in the field.
The work of Kwan and Professors Sondhi and Parameswaran grew out of measurements of the electrical conductivity of twisted bilayers of tungsten ditelluride (WTe2), cooled to a few kelvin above absolute zero. Electrons in an individual WTe2 layer move with comparable speeds in all directions in two dimensions. However, when the two layers are twisted at around 5 degrees, the resulting moiré effect produces a ‘stripy’ potential; electrons moving in this potential propagate relatively freely in the ‘easy’ direction along the stripes, but have great difficulty in moving in the ‘hard’ direction perpendicular to the stripes. WTe2 is one of a family of materials known as transition metal dichalcogenides that can be isolated into 2D layers similarly to graphene. Unlike its counterparts, an isolated layer of WTe2 no longer resembles graphene, meaning that the Oxford team had to combine a mix of pencil-and-paper calculations and detailed numerical simulations to come up with a theoretical model of twisted WTe2.
These groundbreaking experiments were done in the group of Professor Sanfeng Wu, an Assistant Professor of Physics at Princeton University, and also involved collaborators at MIT, Rice University, the Fraunhofer Institute in Hanau, Germany, and the National Institute for Materials Science in Tsukuba, Japan.
Read much more about the research and the questions that remain to be answered on the Department of Physics website.