Spin-, time- and angle-resolved photoemission spectroscopy on WTe$_2$

TL;DR

This study demonstrates the use of spin-, time-, and angle-resolved photoemission spectroscopy with high-harmonic generation to investigate spin polarization and dynamics in WTe$_2$, a candidate Weyl semimetal.

Contribution

It introduces a novel experimental setup combining spin-resolved and time-resolved photoemission with HHG laser sources to study spin phenomena in WTe$_2$.

Findings

Observation of spin accumulation above Weyl points

Evidence of spin-polarized cone-like electronic structure

Validation of STARPES with HHG as a tool for spin dynamics studies

Abstract

We combined a spin-resolved photoemission spectrometer with a high-harmonic generation (HHG) laser source in order to perform spin-, time- and angle-resolved photoemission spectroscopy (STARPES) experiments on the transition metal dichalcogenide bulk WTe$_2$, a possible Weyl type-II semimetal. Measurements at different femtosecond pump-probe delays and comparison with spin-resolved one-step photoemission calculations provide insight into the spin polarization of electrons above the Fermi level in the region where Weyl points of WTe$_2$ are expected. We observe a spin accumulation above the Weyl points region, that is consistent with a spin-selective bottleneck effect due to the presence of spin polarized cone-like electronic structure. Our results support the feasibility of STARPES with HHG, which despite being experimentally challenging provides a unique way to study spin dynamics in photoemission.