Title

Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor CaKFe4As4

Publication Date

4-1-2020

Department

Ames Laboratory; Physics and Astronomy

Campus Units

Ames Laboratory, Physics and Astronomy

OSTI ID+

1615930

Report Number

IS-J 10199

DOI

10.1103/PhysRevB.101.134502

Journal Title

Physical Review B

Volume Number

101

Issue Number

13

First Page

134502

Abstract

The upper critical field of multiband superconductors is an important quantity that can reveal details about the nature of the superconducting pairing. Here we experimentally map out the complete upper-critical-field phase diagram of a stoichiometric superconductor, CaKFe4As4, up to 90T for different orientations of the magnetic field and at temperatures down to 4.2K. The upper critical fields are extremely large, reaching values close to ∼3Tc at the lowest temperature, and the anisotropy decreases dramatically with temperature, leading to essentially isotropic superconductivity at 4.2K. We find that the temperature dependence of the upper critical field can be well described by a two-band model in the clean limit with band-coupling parameters favoring intraband over interband interactions. The large Pauli paramagnetic effects together with the presence of the shallow bands is consistent with the stabilization of an FFLO state at low temperatures in this clean superconductor.

DOE Contract Number(s)

EP/I004475/1; EP/EP/I017836/1; EP/N01085X/1; EP/M020517/1; AC02-07CH11358; GBMF4411

Language

en

Publisher

Iowa State University Digital Repository, Ames IA (United States)

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