Relaxation mechanisms in a disordered system with Poisson-level statistics

We discuss the interplay between many-body localization and spin symmetry. To this end, we study the time evolution of several observables in the anisotropic t-J model. Like the Hubbard chain, the studied model contains charge and spin degrees of freedom, yet it has smaller Hilbert space and thus allows for numerical studies of larger systems. We compare the field disorder that breaks the Z2 spin symmetry and a potential disorder that preserves the latter symmetry. In the former case, sufficiently strong disorder leads to localization of all studied observables, at least for the studied system sizes. However, in the case of symmetry-preserving disorder, we observe that odd operators under the Z2 spin transformation relax towards the equilibrium value at relatively short timescales that grow only polynomially with the disorder strength. On the other hand, the dynamics of even operators and the level statistics within each symmetry sector are consistent with localization. Our results indicate that localization exists within each symmetry sector for symmetry-preserving disorder. Odd operators??? apparent relaxation is due to their time evolution between distinct symmetry sectors.

Automated summary

We discuss the interplay between many-body localization and spin symmetry by studying the time evolution of several observables in the anisotropic t-J model. The results show that odd operators relax towards equilibrium values at short timescales in the case of symmetry-preserving disorder, while even operators and level statistics exhibit localization within each symmetry sector.