Large Transverse Thermoelectric Effect in Weyl Semimetal TaIrTe$_4$ Engineered for Photodetection

TL;DR

This study demonstrates that the large transverse thermoelectric effect in Weyl semimetal TaIrTe$_4$ can be engineered to enhance and control photocurrent responses for broadband photodetection applications.

Contribution

The paper confirms the origin of anomalous photocurrents in TaIrTe$_4$ as a transverse thermoelectric effect and shows how to engineer device geometry and thermal environment to amplify photocurrents.

Findings

Photocurrents in TaIrTe$_4$ originate from a large transverse thermoelectric effect.

Engineering the orientation of edges and electrodes controls photocurrent spatial distribution.

Substrate engineering can locally enhance photocurrent for improved photodetection.

Abstract

Anomalous local photocurrent generation via second-order nonlinear and thermoelectric responses is a signature of many topological semimetals. The emergence of these photocurrents is inherently linked to symmetry breaking and anisotropy of their crystal lattices. Studies of type-II Weyl semimetals of group C$_{2v}$ (WTe$_2$, MoTe$_2$, TaIrTe$_4$) have reported anomalous, nonlocal photocurrents localized to crystals edges or far from electrodes, which are highly dependent on the geometry of the material sample. While originally attributed to a nonlinear charge current response, it was recently shown that these currents could instead be attributed to the anisotropic Seebeck coefficients of the materials. Here, we confirm that anomalous photocurrents observed in TaIrTe$_4$ under either visible or far-infrared far-field illumination originate from the large transverse thermoelectric effect. We engineer the mutual orientation of crystal edges and electrodes as well as the thermal environment of TaIrTe$_4$ to control and amplify its spatial photocurrent response. We show that substrate engineering can locally enhance photocurrent. This framework of thermal device engineering can enable broadband photo detection schemes by leveraging spectral and spatial dependence of photocurrents for applications like wavefront sensing, beam positioning, and edge detection.