Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor CaKFe4As4
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Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.
For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.
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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.
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This article is published as Bristow, Matthew, William Knafo, Pascal Reiss, William Meier, Paul C. Canfield, Stephen J. Blundell, and Amalia I. Coldea. "Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor CaKFe 4 As 4." Physical Review B 101, no. 13 (2020): 134502. DOI: 10.1103/PhysRevB.101.134502. Posted with permission.