Anisotropic Hot Carrier Relaxation and Coherent Phonon Dynamics in Type-II Weyl Semimetal TaIrTe4

TL;DR

This study investigates the anisotropic electron-phonon interactions, coherent phonon dynamics, and thermal conductivity in the type-II Weyl semimetal TaIrTe4, revealing key anisotropic properties relevant for optoelectronic applications.

Contribution

It provides the first detailed analysis of anisotropic EPC, coherent phonon modes, and in-plane thermal conductivity in TaIrTe4, highlighting their impact on device design.

Findings

EPC strength depends on crystal axes and probe polarization.

Identified three coherent phonon modes with anisotropic responses.

Significant in-plane thermal conductivity anisotropy between a and b axes.

Abstract

The unique energy band and crystal structure of the layered type-II Weyl semimetal TaIrTe4 hold great promise for high-performance broadband anisotropic optoelectronic devices. Therefore, gaining an in-depth understanding of the interactions between internal microscopic particles is of vital importance. Here, we employ a two-color pump-probe system to reveal the anisotropic electron-phonon coupling (EPC) and coherent phonon dynamics in bulk TaIrTe4. The carrier relaxation exhibits a four-exponential decay process, with strong dependence on polarization of probe pulse, indicating that EPC strength is closely related to the crystal axes (a/b-axes). In addition, we observe three coherent phonon modes in bulk TaIrTe4: 38.5 GHz, 0.44 THz and 1.29 THz. Their oscillation amplitudes and dephasing times also show anisotropic responses to the probe polarization. We also investigate the in-plane cross-directional thermal conductivity coefficient of TaIrTe4 by beam-offset frequency-domain thermal reflection (FDTR). The thermal conductivity coefficient along the a-axis and b-axis directions are ka=14.4 W/mK and kb=3.8 W/mK, respectively. This represents a significant in-plane anisotropy. Our work not only reveals the key role of anisotropic EPC in controlling the thermal and optical properties of TaIrTe4, but also provides insights into designing polarization-sensitive optoelectronic devices based on topological semimetals.