Time- and Angle-Resolved Photoemission Studies of Quantum Materials

TL;DR

Time- and angle-resolved photoemission spectroscopy (TR-ARPES) is a powerful ultrafast technique that reveals the dynamic electronic properties of quantum materials, advancing understanding of out-of-equilibrium states and phase transitions.

Contribution

This paper reviews recent advances in TR-ARPES technology and its application to diverse quantum materials, highlighting new insights into ultrafast electron dynamics.

Findings

TR-ARPES uncovers out-of-equilibrium electronic states.

It reveals ultrafast spin and electron-phonon dynamics.

Demonstrates phase transitions induced by ultrafast excitation.

Abstract

Angle-resolved photoemission spectroscopy (ARPES) -- with its exceptional sensitivity to both the binding energy and momentum of valence electrons in solids -- provides unparalleled insights into the electronic structure of quantum materials. Over the last two decades, the advent of femtosecond lasers, which can deliver ultrashort and coherent light pulses, has ushered the ARPES technique into the time domain. Now, time-resolved ARPES (TR-ARPES) can probe ultrafast electron dynamics and the out-of-equilibrium electronic structure, providing a wealth of information otherwise unattainable in conventional ARPES experiments. This paper begins with an introduction to the theoretical underpinnings of TR-ARPES followed by a description of recent advances in state-of-the-art ultrafast sources and optical excitation schemes. It then reviews paradigmatic phenomena investigated by TR-ARPES thus far, such as out-of-equilibrium electronic states and their spin dynamics, Floquet-Volkov states, photoinduced phase transitions, electron-phonon coupling, and surface photovoltage effects. Each section highlights TR-ARPES data from diverse classes of quantum materials, including semiconductors, charge-ordered systems, topological materials, excitonic insulators, van der Waals materials, and unconventional superconductors. These examples demonstrate how TR-ARPES has played a critical role in unraveling the complex dynamical properties of quantum materials. The conclusion outlines possible future directions and opportunities for this powerful technique.