Fluctuation Conductivity and Vortex State in Superconductor with Strong Paramagnetic Pair Breaking

TL;DR

This paper investigates how strong paramagnetic pair-breaking influences fluctuation conductivity and vortex states in superconductors, revealing enhanced quantum fluctuations and field-dependent vortex lattice behaviors at low temperatures.

Contribution

It provides a theoretical analysis of fluctuation conductivity under strong PPB, linking vortex lattice states to experimental negative magnetoresistance in FeSe.

Findings

Quantum fluctuation enhancement with stronger PPB.

Field dependence of conductivity varies with vortex lattice type.

Vortex states in FeSe likely involve the second Landau level.

Abstract

The fluctuation conductivity of a moderately clean type II superconductor with strong Pauli paramagnetic pair-breaking (PPB) is studied by focusing on the quantum regime at low temperatures and in high magnetic fields. First, it is pointed out that, as the PPB effect becomes stronger, the quantum superconducting fluctuation is generally enhanced so that the Aslamasov-Larkin (AL) fluctuation conductivity tends to vanish upon cooling. Further, by examining other (the DOS and the Maki-Thompson (MT)) terms of the fluctuation conductivity, the field dependence of the resulting total conductivity is found to depend significantly on the type of the vortex lattice (or, glass) ordered state at low temperatures where the strong PPB plays important roles. By comparing the present theoretical results with the fluctuation-induced negative magnetoresistance behavior upon entering a PPB-induced novel SC phase of Iron selenide (FeSe), it is argued that the vortex matter states of the superconducting order parameter in the second lowest ($n=1$) Landau level are realized in FeSe in the parallel field configuration in high fields and at low temperatures