Reconstruction of attosecond beating by interference of two-photon interband transitions in solids

Abstract

The reconstruction of attosecond beating by interference of two-photon transitions is one of the most widely used techniques for obtaining both the relative phases of harmonics forming an attosecond pulse train and the phase of atomic radiative transitions. If the latter is computed by theory, it allows one to reconstruct the attosecond pulse train; if the former is known experimentally, it allows for reconstruction of the electronic dynamics of photoionization in atomic and molecular systems with attosecond temporal resolution. As it relies on the interference of photoelectrons in vacuum, similar interference has never been contemplated inside crystals. Here we explore the applicability of this scheme to solid-state systems using a one-dimensional model and a density-functional theory--calculated structure of two-dimensional hexagonal boron nitride. We discuss the possibility of (i) reconstructing the relative phases between harmonics with trivial influence of the ``atomic phase'' and (ii) retrieving the relative phases of two-photon transitions through different bands, which are generally challenging to obtain both experimentally and numerically. These phases are recorded in the beating of the population signal arising from interfering two-photon pathways, and can be read out with angle-resolved photoemission spectroscopy. Furthermore, the amplitude of the population beating decays as the pump and probe pulses are separated in time due to electron-hole decoherence, providing a simple interferometric method to extract dephasing times.