Thouless energy and critical statistics on the metallic side of the many-body localization transition

Corentin L. Bertrand, Antonio M. García-García

Published 2016-06-27Version 1

We study a one-dimensional (1d) XXZ spin-chain in a random field on the metallic side of the many-body localization transition by level statistics. For a fixed interaction, and intermediate disorder below the many-body localization transition, we find that asymptotically the number variance grows faster than linear with a disorder dependent exponent. This is consistent with the existence of the Thouless energy in the spectrum. In non-interacting disordered metals this is an energy scale related to the typical time for a particle to diffuse across the sample. In the interacting case it seems related to a more intricate anomalous diffusion process. As disorder is further increased, still on the metallic side, the Thouless energy is gradually washed out. In the range of sizes we can explore, level statistics are scale invariant and approach Poisson statistics at the many-body localization transition. Slightly below the many-body localization transition, spectral correlations, well described by critical statistics, are quantitatively similar to those of a high dimensional, non-interacting, disordered conductor at the Anderson transition. Our results are not in agreement with recent claims in the literature that, close to the transition, spectral correlations are described by semi-Poisson statistics and, for lower disorder, the number variance grows slower than linear.