Instability of subdiffusive spin dynamics in strongly disordered Hubbard chain*

We study spin transport in a Hubbard chain with a strong, random, on-site potential and with spin-dependent hopping integrals t_σ. For the SU(2) symmetric case t_↑ = t_↓, such a model exhibits only partial many-body localization with localized charge and (delocalized) subdiffusive spin excitations [1,2]. In our work [3], we demonstrate that breaking the SU(2) symmetry by even weak spin asymmetry, t_↑ ≠ t_↓, localizes spins and restores full many-body localization. To this end, we derive an effective spin model where the spin subdiffusion is shown to be destroyed by arbitrarily weak t_↑ ≠ t_↓. Instability of the spin subdiffusion originates from an interplay between random effective fields and singularly distributed random exchange interactions.

[1] P. Prelovsek, O. S. Barisic, and M. Znidaric, Phys. Rev. B 94, 241104(R) (2016).
[2] M. Kozarzewski, P. Prelovsek, and M. Mierzejewski, Phys. Rev. Lett. 120, 246602 (2018).
[3] M. Sroda, P. Prelovsek, and M. Mierzejewski, Phys. Rev. B 99, 121110(R) (2019).