Terahertz radiation by subpicosecond spin-polarized photocurrent originating from Dirac electrons in a Rashba-type polar semiconductor

TL;DR

This paper demonstrates that circularly polarized femtosecond laser pulses can generate phase-controlled terahertz radiation from a Rashba-type polar semiconductor by inducing spin-polarized photocurrents through interband transitions.

Contribution

It reveals a novel mechanism for terahertz emission driven by spin-polarized photocurrents in a bulk Rashba semiconductor without external electric fields.

Findings

Terahertz waves are emitted upon resonant excitation of spin-splitting bands.

The phase of terahertz emission is controlled by circular polarization.

Spin-polarized photocurrents originate from asymmetric depopulation of Dirac states.

Abstract

The spin-splitting energy bands induced by the relativistic spin-orbit interaction in solids provide a new opportunity to manipulate the spin-polarized electrons on the sub-picosecond time scale. Here, we report one such example in a bulk Rashba-type polar semiconductor BiTeBr. Strong terahertz electromagnetic waves are emitted after the resonant excitation of the interband transition between the Rashba-type spin-splitting energy bands with a femtosecond laser pulse circularly polarized. The phase of the emitted terahertz waves is reversed by switching the circular polarization. This suggests that the observed terahertz radiation originates from the subpicosecond spin-polarized photocurrents, which are generated by the asymmetric depopulation of the Dirac state. Our result provides a new way for the current-induced terahertz radiation and its phase control by the circular polarization of incident light without external electric fields.