"Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Supe" by Charles C. Agosta, Nathanael A. Fortune et al.
 

Physics

Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Superconductivity above the Paramagnetic Limit

Document Type

Article

Abstract

We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field superconducting state displays the bulk paramagnetic ordering of spin domains required of the FFLO state. These results rule out the alternate possibility of spin-density wave ordering in the high-field superconducting phase. The phase diagram determined from our measurements-including the observation of a phase transition into the FFLO phase at Hp-is in good agreement with recent NMR results and our own earlier tunnel-diode magnetic penetration depth experiments but is in disagreement with the only previous calorimetric report.

Publication Title

Physical Review Letters

Publication Date

6-28-2017

Volume

118

Issue

26

ISSN

0031-9007

DOI

10.1103/PhysRevLett.118.267001

Keywords

inhomogeneous superconductivity, magnetic-field-induced phase transition

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