On the Origin of the Anomalous Upper Critical Field in Quasi-One-Dimensional Superconductors

TL;DR

This paper investigates the upper critical field in quasi-one-dimensional superconductors, revealing it exceeds traditional limits due to fluctuations and unconventional pairing, offering insights into experimental observations in TMTSF salts.

Contribution

It introduces a weak coupling renormalization group analysis showing that quasi-1D fluctuations significantly enhance H_c2 beyond known limits, linked to a d-wave FFLO state.

Findings

H_c2 surpasses Pauli and FFLO limits due to quasi-1D fluctuations

Results suggest a d-wave FFLO state in TMTSF salts

Predicted H_c2 behavior can be tested under pressure

Abstract

Upper critical field, H_c2, in quasi-1D superconductors is investigated by the weak coupling renormalization group technique. It is shown that H_c2 greatly exceeds not only the Pauli limit, but also the conventional paramagnetic limit of the Flude-Ferrell-Larkin-Ovchinnikov (FFLO) state. This increase is mainly due to quasi-1D fluctuations effect as triggered by interference between unconventional superconductivity and density-wave instabilities. Our results give a novel viewpoint on the large H_c2 observed in TMTSF-salts in terms of a d-wave FFLO state that is predicted to be verified by the H_c2 measurements under pressure.