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TT: Fachverband Tiefe Temperaturen

TT 42: Superconductivity: Fabrication, Properties, Electronic Structure

TT 42.1: Talk

Thursday, March 29, 2012, 15:00–15:15, H 3005

Angular-dependent specific heat of the fully organic superconductor β″-(ET)₂SF₅CH₂CF₂SO₃ - evidence for an FFLO phase — •Rico Beyer¹, J.A. Schlueter², and J. Wosnitza¹ — ¹Hochfeld-Magnetlabor (HLD), Forschungszentrum Dresden- Rossendorf (FZD), Dresden, Germany — ²Materials Science Division, Argonne National Laboratory, Argonne, USA

Since 1964 predicted, there is no clear-cut experimental proof of the existence of a field-induced superconducting state with finite center of mass momentum (q ≠ 0) [1]. In 2007, Lortz et al. reported thermodynamic evidence for a FFLO state in κ-(ET)₂Cu(NCS)₂ [2], where ET stands for bisethylenedithio-tetrathiafulvalene. They found an emerging sharp double-peak structure in the specific heat, indicating first-order phase transitions at high magnetic fields applied parallel to the superconducting ET layers. Expecting similar novel results for β″-(ET)₂SF₅CH₂CF₂SO₃, we performed high-resolution specific-heat measurements for different orientations with very fine steps around perfect parallel alignment. In conclusion, we found an upturn in the field-temperature phase diagram of the superconducting phase beyond the Pauli-Clogston limit and we could observe a double-peak structure above 9,4 Tesla but only by tilting the field 0,2 degree out of the ET sheets. Part of this work has been supported by EuroMagNET, EU contract 228043.
P. Fulde and R.A. Ferrel, Phys. Rev. 135, A550 (1964); A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp. Teor. Fiz. 47, 1136 (1964)
R. Lortz et al., Phys. Rev. Lett. 99, 187002 (2007)