Generic (fractional) quantum anomalous Hall crystals from interaction-driven band folding

TL;DR

This paper demonstrates the emergence of fractional quantum anomalous Hall crystals from interaction-driven band folding in a topological flat-band model, revealing new states with coexisting charge density waves and non-trivial mini-bands.

Contribution

It introduces a generic scheme for realizing fractional Hall crystals via doping of topologically folded mini-bands, applicable to both fermionic and bosonic systems.

Findings

Discovery of (F)QAHC states at fractional fillings of mini-bands.

Enlarged ground-state degeneracies due to CDW and mini-band fillings.

Identification of a compressible CDW phase as a precursor to FQAHC.

Abstract

Among the extensive studies of fractional quantum anomalous Hall (FQAH) states, there recently appears a growing interest in the topological states with coexisting charge density wave (CDW) orders. Such states are referred to as Hall crystals. However, compared to those with integer Hall conductivities, the FQAH crystal (FQAHC) is still elusive even at the level of microscopic model. In this work, we numerically study a topological flat-band model on triangular lattice with spinless fermions. At fractional filling of the Chern band, the nearest-neighbor interaction leads to a commensurate and topologically trivial CDW state. Interestingly, the folded mini-band above the CDW gap is non-trivial, and we focus on the doping of it without any projection. A series of (F)QAHC states at (fractional) integer fillings of this mini-band are discovered and some FQAHC state might even exist in less "ideal" conditions. The ground-state degeneracies of such (F)QAHC states are enlarged by the CDW degeneracy and the Hall conductivities -- determined by the fillings of the mini-band -- are different from the fillings of the original Chern band. We also study the thermodynamics of an FQAHC state and find a compressible CDW phase at intermediate temperatures, which might serve as a precursor of lower temperature FQAHC phase. Moreover, we numerically demonstrate that such a generic scheme of doping CDW-folded topological mini-band could be applied to bosonic systems, broadening the platforms of Hall-crystal physics and motivating its exploration in quantum moire and cold-atom systems.