Splitting of topological charge pumping in an interacting two-component fermionic Rice-Mele Hubbard model

TL;DR

This paper investigates how interactions and symmetry-breaking fields affect topological charge pumping in a two-component fermionic Rice-Mele Hubbard model, revealing new splitting phenomena and transport behaviors with potential experimental realizations.

Contribution

It demonstrates the splitting of a topological critical point into two separate points via Hubbard interactions and explores the effects of magnetic fields and spin couplings on charge and spin transport.

Findings

Interaction causes splitting of the topological critical point.

Magnetic fields enable spin transport alongside charge pumping.

Pure charge pumping achieved with Ising spin coupling.

Abstract

A Thouless pump transports an integer amount of charge when pumping adiabatically around a singularity. We study the splitting of such a critical point into two separate critical points by adding a Hubbard interaction. Furthermore, we consider extensions to a spinful Rice-Mele model, namely a staggered magnetic field or an Ising-type spin coupling, further reducing the spin symmetry. The resulting models additionally allow for the transport of a single charge in a two-component system of spinful fermions, whereas in the absence of interactions, zero or two charges are pumped. In the SU(2)-symmetric case, the ionic Hubbard model is visited once along pump cycles that enclose a single singularity. Adding a staggered magnetic field additionally transports an integer amount of spin while the Ising term realizes a pure charge pump. We employ real-time simulations in finite and infinite systems to calculate the adiabatic charge and spin transport, complemented by the analysis of gaps and the many-body polarization to confirm the adiabatic nature of the pump. The resulting charge pumps are expected to be measurable in finite-pumping speed experiments in ultra-cold atomic gases, for which the SU(2) invariant version is the most promising path. We discuss the implications of our results for a related quantum-gas experiment by Walter et al. [arXiv:2204.06561].