# Instability of subdiffusive spin dynamics in strongly disordered Hubbard chain

## TL;DR

This paper investigates how breaking SU(2) symmetry in a disordered Hubbard chain affects spin transport, showing that even weak asymmetry localizes spins and restores full many-body localization, contrasting with the partial localization in the symmetric case.

## Contribution

It demonstrates that weak spin--asymmetry in a disordered Hubbard chain destroys spin subdiffusion and induces full many-body localization, providing an effective spin model analysis.

## Key findings

- Weak spin--asymmetry localizes spins
- Spin subdiffusion is destroyed by any nonzero asymmetry
- Full many-body localization is restored with symmetry breaking

## Abstract

We study spin transport in a Hubbard chain with strong, random, on--site potential and with spin--dependent hopping integrals, $t_{\sigma}$. For the the SU(2) symmetric case, $t_{\uparrow} =t_{\downarrow}$, such model exhibits only partial many-body localization with localized charge and (delocalized) subdiffusive spin excitations. Here, we demonstrate that breaking the SU(2) symmetry by even weak spin--asymmetry, $t_{\uparrow} \ne t_{\downarrow}$, 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 $t_{\uparrow} \ne t_{\downarrow}$. Instability of the spin subdiffusion originates from an interplay between random effective fields and singularly distributed random exchange interactions.