Spin subdiffusion in perturbed infinite-U Hubbard chain

TL;DR

This paper investigates spin dynamics in the perturbed infinite-U Hubbard chain, revealing a transition from ballistic to subdiffusive transport due to Hilbert space fragmentation and charge-mediated spin transport mechanisms.

Contribution

It introduces a detailed analysis of spin transport regimes in integrable and perturbed Hubbard models, highlighting the emergence of subdiffusion due to Hilbert space fragmentation.

Findings

Spin transport varies from ballistic to anomalous diffusion in integrable models.

Perturbed models exhibit diffusion to subdiffusion transition.

Subdiffusion mechanism is distinct from disordered or dipole-conserving systems.

Abstract

The $t$-model represents the Hubbard model in the limit $U \to \infty$ and is one of the basic models of strongly correlated electrons. On a one-dimensional chain, the model is integrable, and the charge dynamics corresponds to that of free spinless fermions. However, the sequence of spins is frozen, leading to the Hilbert space fragmentation and nontrivial spin dynamics. We consider integrable and perturbed models with perturbations that break integrability while preserving fragmentation, and show that they exhibit various types of spin dynamics, from ballistic transport to anomalous diffusion in the integrable case, and from diffusion to subdiffusion in the perturbed case. Due to fragmentation, in all cases considered, spin transport is mediated by charge transport, with a particular magnetization dependence, most notably leading to subdiffusion in the grandcanonical average of the perturbed model, with a mechanism distinct from subdiffusion in disordered or dipole-conserving models.