Exploring New Physics in Moire Materials

Who: Jong Yeon Lee, UC Santa Barbara
Monday, February 7, 2022 - 3:30pm

A CMU-PITT Colloquium 

Abstract: Moire heterostructure is an exciting class of highly-tunable platforms hosting various types of strongly-correlated physics. In this talk, I will present two different emergent quantum phenomena arising in this platform: (i) Correlated insulator and correlated semimetal in twisted graphene layers, and (ii) fractional Chern insulators and emergent quantum electrodynamics in Moire materials under magnetic field.

The first part of the talk covers the rich physics of twisted graphene layers originated from multi-flavored topological flat bands. In particular, I will present the first time unbiased Monte Carlo simulations of realistic twisted bilayer graphene models at charge-neutrality. The results include the emergence of an insulating inter-valley coherent phase in competition with a correlated semi-metal phase, detailed temperature evolution of order parameters, and electronic spectral functions which reveal a pseudogap regime. The second part of the talk covers exotic quantum criticality in Moire systems under magnetic fields. In experiments, fractional Chern insulators have been shown to emerge from the interplay of a magnetic field and a Moire superlattice potential. Using DMRG simulations, I will show that one can induce quantum phase transitions between these phases, and furthermore, I will propose that these phase transitions are described by a new family of quantum critical points described by QED3-Chern-Simons theory with emergent symmetry. This opens a new window to study analytically intractable strongly interacting field theories in condensed matter experiments.