In the past three decades, angle-resolved photoemission spectroscopy (ARPES) has offered one of the most direct way to study the electronic structure of materials. This technique involves the use a light source with sufficient photon energy to eject electrons in vacuum. The kinetic energy and emission angle of these “photoelectrons” are then resolved by an electron analyzer, providing a momentum-space picture of the material’s band dispersion, many-body gaps, electron-boson couplings, electron spin polarization, and band topology. The last years have witnessed three revolutions in ARPES technology.
First, the combination of more advanced electron analyzers, lower temperatures, and laser sources with narrow linewidth have paved the way to electronic structure studies with unprecedented energy resolution. Second, the extension of ARPES into the time domain by means of femtosecond lasers has enabled the observation of fascinating nonequilibrium phenomena and light-induced phase transitions.
Finally, significant improvements in electron optics engineering and aberration correction have opened the doors to photoemission microscopy with spatial resolution down to few nanometers. Altogether, these solutions offer a wealth of opportunities for future developments in the study of quantum materials.
In our lab, we work on implementing innovative schemes for ARPES based on state-of-the-art laser and electron optics instrumentation. On one side, we are interested in developing methods to image the electronic structure of mechanically exfoliated materials and resolve its evolution in space and time. On the other side, we aim to push the selectivity of the pump excitation process in time-resolved ARPES, driving materials far from equilibrium with tailored laser pulses and recording the resulting electronic structure changes.
We perform these studies at low temperature to quench thermal broadening and obtain a clean picture of underlying quantum phenomena. However, our ultimate goal is to find the suitable combination of external stimuli that stabilizes macroscopic quantum properties at room temperature. In this respect, the direct view of the electronic structure via ARPES will offer us a precious guideline to tune materials’ functionalities.