Many-body localization and enhanced non-ergodic sub-diffusive regime in the presence of random long-range interactions

We study many-body localization (MBL) in a one-dimensional system of spinless fermions with a deterministic aperiodic potential in the presence of long-range interactions decaying as power-law $V_{ij}/(r_i-r_j)^alpha$ with distance and having random coefficients $V_{ij}$. We demonstrate that MBL survives even for $alpha <1$ and is preceded by a broad non-ergodic sub-diffusive phase. Starting from parameters at which the short-range interacting system shows infinite temperature MBL phase, turning on random power-law interactions results in many-body mobility edges in the spectrum with a larger fraction of ergodic delocalized states for smaller values of $alpha$. Hence, the critical disorder $h_c^r$, at which ergodic to non-ergodic transition takes place increases with the range of interactions. Time evolution of the density imbalance $I(t)$, which has power-law decay $I(t) sim t^{-gamma}$ in the intermediate to large time regime, shows that the critical disorder $h_{c}^I$, above which the system becomes diffusion-less (with $gamma sim 0$) and transits into the MBL phase is much larger than $h_c^r$. In between $h_{c}^r$ and $h_{c}^I$ there is a broad non-ergodic sub-diffusive phase, which is characterized by the Poissonian statistics for the level spacing ratio, multifractal eigenfunctions and a non zero dynamical exponent $gamma ll 1/2$. The system continues to be sub-diffusive even on the ergodic side ($h < h_c^r$) of the MBL transition, where the eigenstates near the mobility edges are multifractal. For $h < h_{0}<h_c^r$, the system is super-diffusive with $gamma >1/2$. The rich phase diagram obtained here is unique to random nature of long-range interactions. We explain this in terms of the enhanced correlations among local energies of the effective Anderson model induced by random power-law interactions.