Shooting Electronic Structure Movies with Time-resolved Photoemission

Angle-resolved photoemission spectroscopy and its application to topological materials

“…The rapid development of commercially available, high-repetition-rate (≥10 kHz), amplified femto second lasers has led to the increased use of time-resolved ARPES. In the past 10 years, various time-resolved ARPES systems 55,57,[125][126][127][176][177][178][179][180] with different energy reso lution (tens to hundreds of meV), temporal resolution (approximately hundreds of attoseconds 58,59 to hundreds of femto seconds) and pump frequencies (approximately tens of meV to several eV) have been developed, enabling the electron dynamics in correlated materials to be probed. Moreover, by carefully choosing the pump frequency, it is possible to observe new quantum states induced by light, such as Floquet-Bloch states 64,181,182 (discussed below).…”

“…Therefore, the use of sub-picosecond or even sub-femtosecond laser pulses in pump-probe experiments enables one to disentangle the coupled interactions between the charge, spin, lattice and orbital degrees of freedom 157 . In particular, the combination of pump-probe optical spectroscopy with ARPES, namely time-resolved ARPES 37,[40][41][42][44][45][46][47][48][49][50][51][52] , provides direct insights to the energy and momentum dependence of these ultrafast dynamics.…”

“…Moreover, the emergence of light sources with micron-or even nano-scale spot sizes have given rise to the possibility of performing spatially resolved ARPES measurements 31,[96][97][98][99][100] , which will play an irreplaceable role in probing the electronic structure of micro-and nano-scale materials as well as materials with phase separation or multiple domains [101][102][103][104][105][106][107][108][109][110][111][112][113] . Finally, the implementation of time-resolved ARPES with ultrafast lasers or X-ray sources 37,[40][41][42][44][45][46][47][48][49][50][51][52]56,57 not only makes it possible to study ultrafast electronic dynamics in the time domain , but also enables us to probe the unoccupied states above the Fermi energy (E F ) [158][159][160] . These advances have enabled the application of ARPES in topological materials to aid our understanding of their unique band structures and physical properties.…”

Angle-resolved photoemission spectroscopy for the study of two-dimensional materials

“…tr-ARPES Time-resolved ARPES (tr-ARPES) is a hybrid of pump-probe optical spectroscopy and ARPES. By applying ultrafast laser pulses to perturb the equilibrium state, the subsequent ARPES measurements can probe the dynamics of transient state or the unoccupied states of the band structure [ 79 , 80 ]. A typical setup involves a pump laser 1.5 eV and a probe beam 6–7 eV, the latter being driven by a high-harmonic-generation (HHG) source.…”

From carriers and virtual excitons to exciton populations: Insights into time-resolved ARPES spectra from an exactly solvable model

“…Accurate approximations to the fundamental equations of many-body theory are being incessantly developed to relate the intensity and direction of the photocurrent to the behavior of quantum matter in equilibrium as well as nonequilibrium conditions. The relationship between pseudogap, charge ordering and Fermi arcs in high temperature superconductors [1,2], Auger scattering, electron-phonon coupling, plasmonic excitations, and local screening in core excited metals [3][4][5], carrier populations and conduction states in excited semiconductors [6][7][8][9][10], topological order [11], excitonic insulator phases [12,13], excitonic Mott transitions [14] and exciton dynamics [15][16][17][18][19][20][21][22][23][24] in pumped semiconductors is a non exhaustive list of the plethora of different phenomena leaving distinctive footprints in trARPES spectra.…”