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Topological exact flat bands in two dimensional materials under periodic strain

Topological exact flat bands in two dimensional materials under periodic strain
Date & Time
April 28, 2023 (Friday) | 15:30-17:00
Venue
CPD-3.29, Centennial Campus, HKU
Speaker
Professor Kai Sun
Department of Physics, University of Michigan

Public Lecture: Topological exact flat bands in two dimensional materials under periodic strain
 
We study flat bands and their topology in 2D materials with quadratic band crossing points (QBCPs) under periodic strain. In contrast to Dirac points in graphene, where strain acts as a vector potential, strain for QBCPs serves as a director potential with angular momentum quantum number l=2. We prove that when the strengths of the strain fields hit certain "magic" values, exact flat bands with nontrivial Chern numbers emerge in the chiral limit, in strong analogy to magic angle twisted bilayer graphene. These flat bands have ideal quantum geometry for the realization of fractional Chern insulators, and they are always fragile topological. The number of flat bands can be doubled for certain point group, and the interacting Hamiltonian is exactly solvable at integer fillings. We further demonstrate the stability of these flat bands against deviations from the chiral limit and discuss possible realization in 2D materials.

 

Professor Kai Sun

Speaker Professor Kai Sun

Department of Physics, University of Michigan

Professor Kai Sun is an accomplished theoretical physicist. He received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2009 and subsequently held a postdoctoral position at the Joint Quantum Institute at the University of Maryland College Park. In 2012 he joined the University of Michigan as a faculty member. In 2015 he was named a Sloan Research Fellow in Physics, a highly prestigious honor recognizing early-career scientists with outstanding potential. Professor Sun investigates how the interactions between particles in complex systems give rise to emergent phenomena and distinct phases of matter. One of his primary areas of research involves exploring the principles of topology to better understand the behavior of matter. His systematic exploration of novel topological phases has helped to shed new light on some of the most fundamental problems in condensed matter physics. His research has had a significant impact on the field of theoretical physics and he has collaborated with physicists from around the world.

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