Electrically tunable Floquet Weyl photon emission from Dirac semimetal Cd3As2

TL;DR

This paper demonstrates electrical and optical control of Floquet Weyl states in the 3D Dirac semimetal Cd3As2, enabling tunable THz emission and advancing quantum technology applications.

Contribution

It introduces a method to electrically and optically engineer Floquet Weyl states in Cd3As2, a 3D Dirac semimetal, with tunable THz emission capabilities.

Findings

Circularly polarized light induces Floquet Weyl states with chiral nodes.

Electric field shifts the Fermi level, modulating THz emission.

Simultaneous control of longitudinal and transverse photocurrents.

Abstract

The ability to optically engineer the Dirac band and electrically control the Fermi level in two-dimensional (2D) Dirac systems, such as graphene, has significantly advanced quantum technologies. However, similar tunability has remained elusive in three-dimensional Dirac systems. In this work, we demonstrate both optical and electrical tunability of the band structure in the 3D Dirac semimetal Cd3As2. Photoexcitation with circularly polarized light breaks time-reversal symmetry, lifting the degeneracy at Dirac points to transform the material into a Floquet Weyl semimetal with chiral Weyl nodes. This transition induces nonzero Berry curvature, giving rise to helicity-dependent transverse anomalous photocurrents, detectable through terahertz emission at normal incidence. Furthermore, applying an external electric field displaces the Fermi level away from the Dirac point, enlarging the Dirac cone projection leading to a reduced density of states of Fermi arcs. As a result, we achieve precise electrical control over Floquet band engineering, resulting in a large modulation of THz emission. Moreover, at oblique incidence, the circular photon-drag effect induces helicity-dependent longitudinal photocurrents. Simultaneous generation and manipulation of both longitudinal and transverse photocurrents enable precise control of the helicity of emitted THz pulses. These results pave the way for electric field-controlled Floquet Weyl THz sources, offering significant potential for applications in quantum computing and low-power electronics.