Theory of pair density wave on a quasi-one-dimensional lattice in the Hubbard model

TL;DR

This paper investigates the emergence of a spin-singlet pair density wave in a quasi-one-dimensional Hubbard model, revealing conditions for its stability and its mixed frequency components, using RPA and FLEX approximations.

Contribution

It demonstrates the stabilization of a spin-singlet PDW with mixed frequency components in a quasi-1D Hubbard model, highlighting the role of perfect Fermi surface nesting.

Findings

PDW-singlet stabilized near perfect Fermi surface nesting

Dominant even-frequency component without nodal lines

FLEX approximation favors PDW over RPA with self-energy corrections

Abstract

In this study, we examine the superconducting instability of a quasi-one-dimensional lattice in the Hubbard model based on the random-phase approximation (RPA) and the fluctuation exchange (FLEX) approximation. We find that a spin-singlet pair density wave (PDW-singlet) with a center-of-mass momentum of $2k_F$ can be stabilized when the one-dimensionality becomes prominent toward the perfect nesting of the Fermi surface. The obtained pair is a mixture of even-frequency and odd-frequency singlet ones. The dominant even-frequency component does not have nodal lines on the Fermi surface. This PDW-singlet state is more favorable as compared to RPA when self-energy correction is introduced in the FLEX approximation.