Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 36: Superconductivity: Properties, Electronic Structure, Order Parameter
TT 36.8: Vortrag
Freitag, 29. Februar 2008, 12:15–12:30, H 0104
Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov state in a layered organic superconductor — •B. Bergk1, P. H. M. Böttger1, R. Lortz2, Y. Wang2, A. Demuer3, I. Sheikin3, G. Zwicknagl4, Y. Nakazawa5, and J. Wosnitza1 — 1Hochfeld-Magnetlabor Dresden, FZ Dresden-Rossendorf, 01314 Dresden, Germany — 2Department of Condensed Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland — 3Grenoble High Magnetic Field Laboratory, CNRS, 38042 Grenoble, France — 4Institut für Mathematische Physik, Technische Universität Braunschweig, D-38106 Braunschweig, Germany — 5Department of Chemistry, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, Japan
We present specific heat and torque-magnetization data of the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 in high magnetic fields up to 28 T and at low temperatures down to 1.5 K. The magnetic field was aligned perfectly parallel to the superconducting planes of the sample. In that orientation and at low temperatures the upper critical field, Bc2, gets close to the Pauli limit which is about 21 T. But instead of the expected saturation at this field value we observe an upturn of Bc2 towards low temperatures. This comes along with a change of the order of the phase transition from second order to first order. In addition, another first-order phase transition appears below Bc2 in the superconducting state. These features strongly point to the formation of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in the state above the Pauli limit. Our results are in line with the behaviour predicted for FFLO states in two-dimensional systems.