Emergent Weyl nodes and Fermi arcs in a Floquet Weyl semimetal

TL;DR

This paper investigates how circularly polarized laser light induces multiple Weyl nodes and Fermi arcs in a Dirac semimetal, especially in the low-frequency regime where multi-photon processes are significant, revealing highly tunable topological features.

Contribution

It uncovers the emergence of multiple Weyl nodes in a Floquet Weyl semimetal due to multi-photon resonances, with tunable properties based on laser parameters, and develops an effective low-energy theory.

Findings

Multiple Weyl nodes emerge in pairs due to band hybridization.

The number and properties of Weyl nodes are tunable via laser amplitude and frequency.

The low-energy theory matches numerical lattice results for Fermi arcs.

Abstract

When a Dirac semimetal is subject to a circularly polarized laser, it is predicted that the Dirac cone splits into two Weyl nodes and a nonequilibrium transient state called the Floquet Weyl semimetal is realized. We focus on the previously unexplored low-frequency regime, where the upper and lower Dirac bands resonantly couple with each other through multi-photon processes, which is a realistic situation in solid state ultrafast pump-probe experiments. We find a series of new Weyl nodes emerging in pairs when the Floquet replica bands hybridize with each other. The nature of the Floquet Weyl semimetal with regard to the number, locations, and monopole charges of these Weyl nodes is highly tunable with the amplitude and frequency of the light. We derive an effective low energy theory using Brillouin-Wigner expansion and further regularize the theory on a cubic lattice. The monopole charges obtained from the low-energy Hamiltonian can be reconciled with the number of Fermi arcs on the lattice which we find numerically.