A versatile laser-based apparatus for time-resolved ARPES with micro-scale spatial resolution

TL;DR

This paper introduces a versatile laser-based time-resolved ARPES system with micrometer spatial resolution, enabling detailed study of ultrafast electron dynamics in inhomogeneous and exfoliated materials.

Contribution

The authors developed a novel apparatus combining high spatial, energy, and temporal resolution for time-resolved ARPES, capable of probing micro-scale samples and inhomogeneous materials.

Findings

Correlated spectral broadening of Bi₂Se₃ surface state with probe size.

Resolved spatial inhomogeneity effects on spectral broadening.

Demonstrated ultrafast electron dynamics measurement on WTe₂ flakes.

Abstract

We present the development of a versatile apparatus for a 6.2 eV laser-based time and angle-resolved photoemission spectroscopy with micrometer spatial resolution (time-resolved $\mu$-ARPES). With a combination of tunable spatial resolution down to $\sim$11 $\mu$m, high energy resolution ($\sim$11 meV), near-transform-limited temporal resolution ($\sim$280 fs), and tunable 1.55 eV pump fluence up to $\sim$3 mJ/cm$^2$, this time-resolved $\mu$-ARPES system enables the measurement of ultrafast electron dynamics in exfoliated and inhomogeneous materials. We demonstrate the performance of our system by correlating the spectral broadening of the topological surface state of Bi$_2$Se$_3$ with the spatial dimension of the probe pulse, as well as resolving the spatial inhomogeneity contribution to the observed spectral broadening. Finally, after in-situ exfoliation, we performed time-resolved $\mu$-ARPES on a $\sim$30 $\mu$m few-layer-thick flake of transition metal dichalcogenide WTe$_2$, thus demonstrating the ability to access ultrafast electron dynamics with momentum resolution on micro-exfoliated and twisted materials.