Anomalous flux quantization in a Hubbard ring with correlated hopping

TL;DR

This paper provides an exact solution for a generalized Hubbard ring with occupation-dependent hopping, revealing conditions under which anomalous flux quantization and superconducting correlations emerge, despite the absence of true superconductivity in certain limits.

Contribution

It introduces an exactly solvable model of a Hubbard ring with correlated hopping and analyzes how small modifications induce superconducting correlations and anomalous flux quantization.

Findings

Degenerate ground states include $ ext{eta}$-pairing states with off-diagonal long-range order.

Small $t_{AB}$ breaks degeneracy and induces superconducting correlations.

Anomalous flux quantization observed under moderate repulsive interactions.

Abstract

We solve exactly a generalized Hubbard ring with twisted boundary conditions. The magnitude of the nearest-neighbor hopping depends on the occupations of the sites involved and the term which modifies the number of doubly occupied sites $t_{AB}=0$. Although $\eta$-pairing states with off-diagonal long-range order are part of the degenerate ground state, the behavior of the energy as a function of the twist rules out superconductivity in this limit. A small $t_{AB}$ breaks the degeneracy and for moderate repulsive $U$ introduce superconducting correlations which lead to ``anomalous'' flux quantization. PACS numbers: 74.20Mn, 71.27.+a, 71.30+h, 71.28.+d