FFLO Superconductivity near the Antiferromagnetic Quantum Critical Point

TL;DR

This paper investigates the stability and characteristics of the FFLO superconducting state near the antiferromagnetic quantum critical point using the two-dimensional Hubbard model and FLEX approximation, revealing results consistent with experiments.

Contribution

It demonstrates the stability of the FFLO state near AFQCP despite quasiparticle scattering and analyzes its phase diagram and magnetic transition features.

Findings

FFLO state remains stable near AFQCP despite spin fluctuation scattering.

Large positive slope of H_{FFLO} with respect to temperature observed.

Convex curvature of the critical magnetic field H_{FFLO} matches experimental data.

Abstract

The Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state near the antiferromagnetic quantum critical point (AFQCP) is investigated by analyzing the two dimensional Hubbard model on the basis of the fluctuation exchange (FLEX) approximation. The phase diagram against the magnetic field and temperature is compared with that obtained in the BCS theory. We discuss the influences of the antiferromagnetic spin fluctuation through the quasiparticle scattering, retardation effect, parity mixing and internal magnetic field. It is shown that the FFLO state is stable in the vicinity of AFQCP even though the quasiparticle scattering due to the spin fluctuation is destructive to the FFLO state. The large positive slope dH_{FFLO}/dT and the convex curvature (d^{2}H_{FFLO}/dT^{2} > 0) are obtained, where H_{FFLO} is the critical magnetic field for the second order phase transition from the uniform BCS state to the FFLO state. These results are consistent with the experimental results in CeCoIn_5. The possible magnetic transition in the FFLO state is examined.