Signature of Many-Body Localization of Phonons in Strongly Disordered Superlattices

The experimental realization of many-body localization (MBL) in solid-state systems has remained challenging. In parallel, open questions remain on the localization of phonons as the strong interactions and disorders in phononic superlattice systems would call for an MBL description. The elucidation of phonon localization through the lens of MBL would have major implications for connecting the MBL phenomenology to a mesoscopic solid-state system. In this talk, I will report evidence of a possible phonon MBL phase in disordered GaAs/AlAs superlattices. Using grazing-incidence inelastic X-ray scattering, we observe a strong deviation of the phonon population in samples doped with ErAs nanodots at low temperature, signaling a departure from thermalization. This behavior occurs within finite phonon energy and wavevector windows, suggesting a localization-thermalization crossover. We support our observation by proposing a theoretical model for the effective phonon Hamiltonian in disordered superlattices, and showing that it can be mapped exactly to a disordered 1D Bose–Hubbard model with a known MBL phase. Our study opens up new opportunities as a new experimental solid-state platform for realizing possible MBL phenomena, and as a novel phonon phase far away from equilibrium.