Nonequilibrium transport and thermalization in strongly disordered 2D electron systems*

Understanding the dynamics of isolated disordered systems and its dependence on the range of interactions has been attracting a lot of research attention in recent years, but many questions remain open, especially in two spatial dimensions.  At the same time, experiments have been limited mostly to those on synthetic quantum matter, such as ultracold atoms in optical lattices and superconducting qubits.  However, observing the absence of thermalization and signatures of many-body localization (MBL) in real, solid-state materials has been a challenge.  

This talk will describe experimental studies of nonequilibrium dynamics in strongly disordered, 2D electron systems with weak thermal coupling to the environment.  We find that, while reducing the range of the Coulomb interaction has practically no effect on the dc transport, there is a striking difference in the dynamics.  In the case of a long-range Coulomb interaction (~1/r), the system thermalizes, although the dynamics is glassy.  In contrast, in the case of a screened or dipolar Coulomb interaction (~1/r³), the thermalization is anomalously slow and strongly sensitive to coupling to the thermal bath, consistent with the proximity to a MBL phase. This direct observation of the MBL-like, prethermal regime in an electronic system thus clarifies the effects of the interaction range on the fate of glassy dynamics and MBL in 2D.  These are important insights for theory, especially since the results have been obtained on systems that are much closer to a thermodynamic limit than synthetic ensembles of interacting, disordered particles employed in previous studies of MBL.  By establishing a new, versatile solid-state platform for the study of MBL, our work also opens new possibilities for further investigations, such as noise measurements as a probe of ergodicity breaking and many-body entanglement.