Correlated insulators and excitations in twisted bilayer graphene

Prof. Biao Lian, Princeton University
Sat, 2021-03-06 10:00 - 11:00
ZOOM link:; PIN: 989397

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.

Prof. Lian received his bachelor degree from Tsinghua University in 2012 and PhD from Prof. Shoucheng Zhang’s group in Stanford University in 2017. He has worked as a postdoctoral research fellow at Princeton Center for Theoretical Science in Princeton University from 2017 to 2020. He has been hired as an assistant professor in the department of physics, Princeton University since 2020. He becomes a Sloan Research Fellow in 2021. Prof. Lian’s research interests extend over the theoretical studies of topological phases of matter, quantum Hall systems, low-dimensional strongly interacting systems, and the entanglement and quantum dynamics of many-body systems, as well as in exploring the connections between condensed matter and high-energy theories.