Excited quantum Hall effect: enantiomorphic flat bands in a Yin-Yang Kagome lattice

TL;DR

This paper introduces a theoretical model of excited-state quantum Hall effect (EQHE) driven by circularly polarized light in a Yin-Yang Kagome lattice, enabling chirality switching without magnetization.

Contribution

It proposes a novel non-equilibrium EQHE mechanism based on photoexcitation between enantiomorphic flat bands, expanding understanding of topological states without intrinsic magnetization.

Findings

Chirality of edge states can be reversed by light's handedness.

EQHE occurs without magnetic order, driven by optical excitation.

Potential for optically controlled topological devices.

Abstract

Quantum Hall effect (QHE) is one of the most fruitful research topics in condensed-matter physics. Ordinarily, the QHE manifests in a ground state with time-reversal symmetry broken by magnetization to carry a quantized chiral edge conductivity around a two-dimensional insulating bulk. We propose a theoretical concept and model of non-equilibrium excited-state QHE (EQHE) without intrinsic magnetization. It arises from circularly polarized photoexcitation between two enantiomorphic flat bands of opposite chirality, each supporting originally a helical topological insulating state hosted in a Yin-Yang Kagome lattice. The chirality of its edge state can be reversed by the handedness of light, instead of the direction of magnetization as in the conventional quantum (anomalous) Hall effect, offering a simple switching mechanism for quantum devices. Implications and realization of EQHE in real materials are discussed.