Absence of localization in interacting spin chains with a discrete symmetry

Understand

We prove that spin chains symmetric under a combination of mirror and spin-flip symmetries and with a nondegenerate spectrum show finite spin transport at zero total magnetization and infinite temperature.

• We demonstrate this numerically using two prominent examples: the Stark many-body localization system and the symmetrized many-body localization system.
• We provide evidence of delocalization at all energy densities and show that the delocalization mechanism is robust to breaking the symmetry.
• We use our results to construct two localized systems which, when coupled, delocalize each other.