Edge states of Floquet-Dirac semimetal in a laser-driven semiconductor quantum-well

TL;DR

This paper demonstrates that a laser-driven semiconductor quantum-well can host Floquet-Dirac semimetal phases with unique edge states, tunable by laser intensity and boundary conditions, revealing new non-equilibrium topological phenomena.

Contribution

It introduces a novel Floquet-Dirac semimetal phase in a semiconductor quantum-well driven by a continuous wave laser, with tunable edge states and boundary-condition-dependent properties.

Findings

Laser-driven quantum-well exhibits Floquet-Dirac semimetal phase.

Edge states mediate topological transitions controlled by laser intensity.

Nearly fourfold-degenerate points influence edge state properties.

Abstract

Band crossings observed in a wide range of condensed matter systems are recognized as a key to understand low-energy fermionic excitations that behave as massless Dirac particles. Despite rapid progress in this field, the exploration of non-equilibrium topological states remains scarce and it has potential ability of providing a new platform to create unexpected massless Dirac states. Here we show that in a semiconductor quantum-well driven by a cw-laser with linear polarization, the optical Stark effect conducts bulk-band crossing, and the resulting Floquet-Dirac semimetallic phase supports an unconventional edge state in the projected one-dimensional Brillouin zone under a boundary condition that an electron is confined in the direction perpendicular to that of the laser polarization. Further, we reveal that this edge state mediates a transition between topological and non-topological edge states that is caused by tuning the laser intensity. We also show that the properties of the edge states are strikingly changed under a different boundary condition. It is found that such difference originates from that nearly fourfold-degenerate points exist in a certain intermediate region of the bulk Brillouin zone between high-symmetry points.