Coexistence of diffusive and ballistic transport in a simple spin ladder

TL;DR

This paper demonstrates that a nonintegrable spin ladder model exhibits both ballistic and diffusive magnetization transport modes coexisting in different invariant subspaces, revealing complex transport behavior in quantum chaotic systems.

Contribution

It uncovers the coexistence of ballistic and diffusive transport in a simple nonintegrable spin ladder, highlighting the presence of ballistic subspaces within quantum chaotic systems.

Findings

Invariant subspaces support ballistic transport

Complementary subspaces exhibit diffusive transport

Model reduces to the 1D Hubbard model at infinite anisotropy

Abstract

We show that in a nonintegrable spin ladder system with the XX type of coupling along the legs and the XXZ type along the rungs there are invariant subspaces that support ballistic magnetization transport. In the complementary subspace the transport is found to be diffusive. This shows that (i) quantum chaotic systems can possess ballistic subspaces, and (ii) diffusive and ballistic transport modes can coexist in a rather simple nonintegrable model. In the limit of an infinite anisotropy in rungs the system studied is equivalent to the one-dimensional Hubbard model.