Floquet Engineering of Nonequilibrium Valley-Polarized Quantum Anomalous Hall Effect with Tunable Chern Number

TL;DR

This paper demonstrates how Floquet engineering with circularly polarized light can induce and tune valley-polarized quantum anomalous Hall effects with variable Chern numbers in 2D materials, expanding the possibilities for topological phases.

Contribution

It introduces a method to realize and control nonequilibrium VP-QAHE with tunable Chern numbers in realistic materials using Floquet engineering and light irradiation.

Findings

VP-QAHE is present in various 2D materials under circularly polarized light.

The Chern number of VP-QAHE can be tuned up to ±4 by adjusting light parameters.

Valley-resolved chiral edge states and quantized Hall conductance are observed.

Abstract

Numerous attempts have been made so far to explore the quantum anomalous Hall effect (QAHE), but the ultralow observed temperature strongly hinders its practical applications. Hence, it is of great interest to go beyond the existing paradigm of QAHE. Here, we propose that Floquet engineering offers a strategy to realize the QAHE via hybridization of Floquet-Bloch bands. Based on first-principles calculations and Floquet theorem, we unveil that nonequilibrium valley-polarized QAHE (VP-QAHE), independent of magnetic orders, is widely present in ferromagnetic and nonmagnetic members of two-dimensional family materials $M$Si$_2$$Z_4$ ($M$ = Mo, W, V; $Z$ = N, P, As) by irradiating circularly polarized light (CPL). Remarkably, by tuning the frequency, intensity, and handedness of incident CPL, the Chern number of VP-QAHE is highly tunable and up to $\mathcal{C}=\pm 4$. We reveal that such Chern number tunable VP-QAHE attributes to light-induced trigonal warping and multiple band inversion at different valleys. The valley-resolved chiral edge states and quantized plateau of Hall conductance, which facilitates the experimental measurement, are visible inside the global band gap. Our work not only establishes Floquet Engineering of nonequilibrium VP-QAHE with tunable Chern number in realistic materials, but also provides a promising avenue to explore emergent topological phases under light irradiation.