$\eta$-pairing on bipartite and non-bipartite lattices

TL;DR

This paper investigates $ta$-pairing states in square and triangular lattices within the attractive Hubbard model under strong Zeeman fields, revealing the role of odd-frequency pairing in electromagnetic stability.

Contribution

It identifies and analyzes $ta$-pairing states on non-bipartite lattices and explores their electromagnetic stability, including the impact of odd-frequency pairing.

Findings

Multiple $ta$-pairing states identified on square and triangular lattices.

Odd-frequency pairing is essential for diamagnetic response in staggered phases.

Stability of $ta$-pairing states depends on electromagnetic response calculations.

Abstract

The $\eta$-pairing is a type of Cooper pairing state in which the phase of the superconducting order parameter is aligned in a staggered manner, in contrast to the usual BCS superconductors with a spatially uniform phase. In this study, we search for a characteristic $\eta$-pairing state in a triangular lattice where a simple staggered alignment of the phase is not possible. As an example, we consider the attractive Hubbard model on both the square and triangular lattices under strong external Zeeman field. Using the mean-field approximation, we have identified several $\eta$-pairing states. Additionally, we have examined the electromagnetic stability of the pairing state by calculating the Meissner kernel. Odd-frequency pairing plays a crucial role in achieving diamagnetic response if the electrons experience a staggered superconducting phase during the propagation of current.