Anomalous Flux Quantization in the Spin-Imbalanced Attractive Hubbard Ring

TL;DR

This study explores flux quantization phenomena in a one-dimensional attractive Hubbard ring with imbalanced spins, revealing anomalous flux quanta related to system size and electron number, consistent with theoretical predictions.

Contribution

It demonstrates the occurrence of anomalous flux quantization of period h=4e in a spin-imbalanced Hubbard ring, extending understanding beyond mean-field predictions.

Findings

Observation of flux quanta h=(N_L - N_e)e.

Detection of spatial oscillations in pairing correlations.

Confirmation of flux quantization period h=4e in strong coupling regime.

Abstract

We investigate the one-dimensional Hubbard ring with attractive interaction in the presence of imbalanced spin populations by using the exact diagonalization method. The singlet pairing correlation function is found to show spatial oscillations with power-law decay as expected in the Fulde-Ferrell-Larkin-Ovchinnikov state of a Tomonaga-Luttinger liquid. In the strong coupling regime, the system shows an anomalous flux quantization of period h=4e, half of the superconducting flux quantum of h=2e, as recently predicted by mean-field analysis, together with various flux quanta smaller than h=4e. Notably, the observed flux quanta are determined by the difference between the system size NL and electron number N_e as h=(N_L-N_e)e.