Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission

TL;DR

This study reveals ultrafast photothermoelectric effects in Dirac semimetal Cd3As2 through terahertz emission, demonstrating significant enhancement under magnetic fields and potential for high-field thermoelectric applications.

Contribution

It uncovers the transient photothermoelectric response in Cd3As2, including the photo-Seebeck and photo-Nernst effects, and shows magnetic field enhancement of these effects.

Findings

THz emission due to photothermoelectric effects confirmed

Magnetic field enhances photothermoelectric current by an order of magnitude

Photothermoelectric conversion efficiency comparable to conventional semiconductors

Abstract

The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd3As2, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd3As2. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.