Group Meetings Schedule 2024

Jan 29, Sayan Choudhury, Monday 9:00 am Pitt time (10:00 PM Beijing time)

Feb 7, Simon Shi, Wednesday 8:30 pm Pitt time (Thu, Feb 8, 9:30 AM Beijing time)

Title: Magic of Topological Moiré Bands — Fractional and Integer Quantum Anomalous Hall Effects

Abstract: Moiré superlattices are exciting platforms to study interaction-driven exotic phases of matter. I will mainly present my recent doctoral work motivated by the observation of fractional quantum anomalous Hall effect in twisted homobilayer transitional metal dichalcogenides. An adiabatic approximation, which maps the moiré bands to a hole gas in a nonuniform periodic pseudo-magnetic field and a periodic potential, has been proposed to explain the occurrence of the flat band and ideal quantum geometry. We show that the adiabatic approximation is accurate under realistic conditions, and that the ideal quantum geometry arises from a partial Aharonov-Casher cancellation between the magnetic field and the potential. Interestingly, higher-shell Fourier components of the residual potential do not strongly violate the ideal quantum geometry though they do change wave functions. Next, I will briefly present my earlier work on twisted bilayer graphene aligned with hexagonal boron nitride (hBN), in which we propose that the appearance or absence of quantum anomalous Hall effect depends on the commensurability between the two moiré patterns, one between the two graphene layers and the other between the hBN and its adjacent graphene layer.

Feb 14, Nikolay Yegovtsev, Wednesday 8:30 pm Pitt time (Thu, Feb 15, 9:30 AM Beijing time)

Title: Exact results for heavy unitary Bose polarons

Abstract: We consider the problem of unitary Bose polarons, i.e., impurities interacting via a potential with infinite scattering length with a bath of weakly interacting bosons. We show that this problem can be solved analytically in two regimes, where the impurity-boson interaction potential has a range both much smaller and larger than the healing length of the bath. We provide various expressions for the energy and other quasiparticle properties of the polaron in those regimes. Furthermore, we perform numerically exact Diffusion Monte Carlo calculations and we demonstrate that the simple Gross-Pitaevskii theory provides a remarkably accurate description of heavy unitary Bose polarons throughout the whole experimentally relevant range of gas densities.

Feb 21, Anupam Mitra, Wednesday 8:30 pm Pitt time (Thu, Feb 22, 9:30 AM Beijing time)

Daylight Savings Time Starts

Mar 13, Hongyu Wang, Wednesday 9:00 pm Pitt time (Thu, Mar 14, 9:00 AM Beijing time)

Mar 27, Bao-Zong Wang, Wednesday 9:00 am Pitt time (Thu, Mar 28,9:00 AM Beijing time)

Apr 10, Xin-Chi Zhou, Wednesday 9:00 am Pitt time (Thu, Apr 11, 9:00 AM Beijing time)

Apr 24, Haoran Sun, Wednesday 9:00 am Pitt time (Thu, Apr 25, 9:00 AM Beijing time)

May 8, Adham Mahmoud Helmi, Wednesday 9:00 am Pitt time (Thu, May 9, 9:00 AM Beijing time)

May 22, Yi Peng, Wednesday 9:00 am Pitt time (Thu, May 23, 9:00 AM Beijing time)