Fulde–Ferrell–Larkin–Ovchinnikov State in Quasi-One-Dimensional Systems: Correlation between Fermi-Surface Distortion and Optimal In-Plane Magnetic-Field Direction

Itahashi Katsumi

Shimahara Hiroshi

Journal of the Physical Society of Japan

The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state is systematically examined in a generic model of quasi-one-dimensional (Q1D) type-II superconductors that has six hopping integrals of electrons as model parameters. For a magnetic field parallel to the conductive layers, the upper critical field Hc2 is strongly enhanced by the FFLO state at low temperatures and sensitively depends on the angle ϕ between the in-plane magnetic field and the highly conductive chain (the crystal a-axis). As a result, Hc2 exhibits sharp peaks at the optimal angles ϕ = ±ϕ0. Since the optimal angle ϕ0 strongly depends on the structure of the Fermi surface, we examine their correlation, searching for an intuitive method to find ϕ0 from the shape of the Fermi surface. For this purpose, we define quantities that quantify the warp of each sheet (kx > 0 or kx < 0) of the Q1D open Fermi surface and the shear distortion between the two sheets. We estimate the optimal angles for numbers of the parameter sets chosen systematically from a large area of the parameter space. It is found that in most cases, the optimal direction of the in-plane magnetic field tends to be roughly parallel to the a-axis. This result, together with the fact that the orbital pair-breaking effect is weakest for ϕ = 0, implies that the FFLO state is most stabilized for a small ϕ. However, when the warp is small while the shear distortion is moderate, the FFLO state can be maximally stabilized for any in-plane magnetic-field direction except for the directions between the b- and b′-axes, where the b′-axis is perpendicular to the a-axis. The phase diagrams of the optimal angle and the upper critical field at zero temperature are also presented. A jump of the optimal angle ϕ0 when the pressure varies is predicted.

英語

The Physical Society of Japan

Copyright (c) 2020 The Physical Society of Japan

This is not the published version. Please cite only the published version. この論文は出版社版ではありません。引用の際には出版社版をご確認、ご利用ください。

[ISSN] 0031-9015

[DOI] 10.7566/JPSJ.89.024708

[DOI] https://doi.org/10.7566/JPSJ.89.024708