Fractional Chern insulator states in an isolated flat band of zero Chern number

Date

Jun 17, 2025

Time

11:00 AM - 12:00 PM

Speaker

Dr. Zuzhang Lin

Affiliation

Department of Physics, The University of Hong Kong

Language

en

Main Topic

Materialien

Host

Grit Rötzer

Description

A flat band with zero Chern number, and well isolated from the rest of Hilbert space by a gap much larger than interaction strength, is a context that has not been regarded as relevant for fractional quantum Hall physics. In this work, we present a numerical study to demonstrate the emergence of fractional Chern insulator (FCI) states in such isolated flat band with zero Chern number, which is hosted by a fluxed dice lattice with anisotropic hopping strength. While being topologically trivial, this flat band features an intriguing quantum geometry: the difference between the trace of quantum metric tensor and the Berry curvature is a constant. We consider nearest-neighbor repulsion that is weak enough to ensure that the isolated band limit is always satisfied, where band renormalization by interaction leaves the flat band quantum geometry unchanged and introduce a tiny band width only. At filling of the isolated flat band, our exact diagonalization calculations show unambiguous evidences for the FCI states, both from the many-body spectra and the many-body Chern number that demonstrates a fractionally quantized Hall conductance of e^2/3h. And the 3-fold ground state degeneracy on torus suggests that band-folding Hall crystal scenario is not compatible with the observed quantized Hall conductance at 2/3 filling. We find the finite dispersion acquired from interaction renormalization, albeit tiny in the isolated band limit, is necessary for FCI to emerge. With anisotropy getting stronger towards the disconnected-chains limit, the FCI undergoes a topological phase transition to inter-chain charge density wave. .

Links

• Seminars at the IFW

Last modified: Jun 17, 2025, 7:36:14 AM