Colloquium:Correlated insulators and excitations in twisted bilayer graphene (Prof. Biao Lian，Mar.6）

Colloquium

Title: Correlated insulators and excitations in twisted bilayer graphene

Speaker: Prof. Biao Lian, Princeton University

Location: ZOOM link: https://zoom.com.cn/j/69073689152; PIN: 989397

Time: Sat, 2021-03-06 10:00-11:00

Abstract:

The magic angle twisted bilayer graphene (TBG) are known to host flat electronic bands, which exhibit both superconductor and correlated insulator phases. We study the low energy states of the flat-band projected TBG Hamiltonian with Coulomb interactions. By treating the nonchiral interaction and the kinetic energy as perturbations, we analytically derive the exact or perturbative strongly interacting (Chern) insulator ground states at all integer fillings |\nu|<=4. We find the ground state has Chern number mod(\nu,2), and is intervalley coherent (valley polarized) at fillings |\nu|=0,1,2 (|\nu|=3). We further show that the insulators have analytically computable charge 0, +-1,+-2 excitations. These excitation spectra suggest the absence of Cooper pairing from the Coulomb interaction in the flat band limit.