Photoinduced valley and electron-hole symmetry breaking in $ \alpha$-$T_3$ lattice: The role of a variable Berry phase

TL;DR

This study explores how intense circularly polarized light affects the electronic properties of the $ ext{alpha}$-$T_3$ lattice, revealing valley and electron-hole symmetry breaking influenced by the Berry phase, with analytical and numerical insights.

Contribution

It provides exact analytical expressions for quasienergies at Dirac points for all $ ext{alpha}$ and field strengths, and demonstrates the Berry phase's impact on quasienergy and symmetry breaking.

Findings

Quasienergy band gaps decrease with increasing $ ext{alpha}$.

The flat band remains unchanged in dice lattice but disperses for $0< ext{alpha}<1$.

Valley degeneracy and electron-hole symmetry are broken for $0< ext{alpha}<1$.

Abstract

We consider $\alpha$-$T_3$ lattice illuminated by intense circularly polarized radiation in terahertz regime. We present quasienergy band structure, time-averaged energy spectrum and time-averaged density of states of $\alpha$-$T_3$ lattice by solving the Floquet Hamiltonian numerically. We obtain exact analytical expressions of the quasienergies at the Dirac points for all values of $\alpha$ and field strength. We find that the quasienergy band gaps at the Dirac point decrease with increase of $\alpha$. Approximate forms of quasienergy and band gaps at single and multi-photon resonant points are derived using rotating wave approximation. The expressions reveal a stark dependence of quasienergy on the Berry phase of the charge carrier. The quasi energy flat band remains unaltered in presence of radiation for dice lattice ($\alpha=1$). However, it acquires a dispersion in and around the Dirac and even-photon resonant points when $0<\alpha<1$. The valley degeneracy and electron-hole symmetry in the quasienergy spectrum are broken for $0<\alpha<1$. Unlike graphene, the mean energy follows closely the linear dispersion of the Dirac cones till near the single-photon resonant point in dice lattice. There are additional peaks in the time-averaged density of states at the Dirac point for $0 < \alpha \leq 1$.