Pauli-Limited Superconductivity with Classical Magnetic Fluctuations

TL;DR

This paper investigates how classical magnetic fluctuations influence the phase transitions in two-dimensional superconductors under magnetic fields, revealing a shift from second to first order transitions near magnetic instabilities.

Contribution

It introduces a theoretical framework to analyze the impact of magnetic fluctuations on the superconducting phase diagram, especially on the nature of phase transitions.

Findings

Magnetic fluctuations can induce first-order transitions at intermediate temperatures.

The transition into the FFLO state can be driven first order by magnetic fluctuations.

Thermodynamic signatures of the transition are characterized along the critical field.

Abstract

We examine the effect of classical magnetic fluctuations on the phase diagram of paramagneticallylimited two-dimensional superconductors under a Zeeman magnetic field. We derive the free energy expansion in powers of the superconducting order parameter and analyze the character of the normalsuperconducting transition. While the transition is of the second order for all temperatures in the absence of magnetic fluctuations, we find that proximity to magnetism drives both the transition into the uniform state and that into the modulated (Fulde-Ferrell-Larkin-Ovchinnikov, FFLO) state to first order at intermediate temperatures. We compute the thermodynamic signatures of the normal-superconducting transition along the upper critical field.