Ultrafast Carrier Dynamics in the Large Magnetoresistance Material WTe$_{2}$

TL;DR

This study uses ultrafast optical spectroscopy to investigate carrier relaxation processes in WTe₂, revealing electron-phonon interactions and temperature-dependent recombination dynamics linked to its large magnetoresistance.

Contribution

It provides the first detailed characterization of ultrafast carrier dynamics and electron-phonon coupling in WTe₂, connecting these processes to its magnetoresistive properties.

Findings

Fast sub-picosecond electron-phonon thermalization process identified.

Slower 5-15 ps phonon-assisted electron-hole recombination observed.

Recombination time decreases below 50 K, indicating electronic structure changes.

Abstract

Ultrafast optical pump-probe spectroscopy is used to track carrier dynamics in the large magnetoresistance material WTe$_{2}$. Our experiments reveal a fast relaxation process occurring on a sub-picosecond time scale that is caused by electron-phonon thermalization, allowing us to extract the electron-phonon coupling constant. An additional slower relaxation process, occurring on a time scale of $\sim$5-15 picoseconds, is attributed to phonon-assisted electron-hole recombination. As the temperature decreases from 300 K, the timescale governing this process increases due to the reduction of the phonon population. However, below $\sim$50 K, an unusual decrease of the recombination time sets in, most likely due to a change in the electronic structure that has been linked to the large magnetoresistance observed in this material.