J. Phys. I France
Volume 6, Numéro 12, December 1996
Page(s) 2051 - 2060
DOI: 10.1051/jp1:1996203
J. Phys. I France 6 (1996) 2051-2060

Anomalous Behavior of the Thermoelectric Power in the Vicinity of the Superconducting Transition in the Organic Superconductors $\mathsf{\kappa}$-(BEDT-TTF) $\mathsf{_2}$Cu(NCS) $\mathsf{_2}$ and $\mathsf{\kappa}$-(BEDT-TTF) $\mathsf{_2}$Cu[ N(CN) $\mathsf{_2}$] Br

G.Yu. Logvenov1, 2, M.V. Kartsovnik1, H. Ito2, T. Ishiguro2, M. Kund3, G. Saito2, S. Takasaki4, J. Yamada4 and H. Anzai4

1  Institute of Solid State Physics, Russian Academy of Science, Chernogolovka, Moscow district, 142432, Russia
2  Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan
3  Walther-Meissner-Institute für Tieftemperaturforschung, Walther-Meissner-Strasse 8, Garching, 85748, Germany
4  Faculty of Science, Himeji Institute of Technology, Kamigori, Hyogo 678-12, Japan

(Received 10 March 1996, revised 20 April 1996, accepted 11 June 1996)

The in-plane thermoelectric power (TEP) of the layered organic superconductors $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 and $\kappa$-(BEDT-TTF) 2Cu[ N(CN) 2] Br has been studied in the vicinity of the superconducting transition under magnetic field. Below the transition temperature, an anomalous non-monotonic behavior of the TEP is found in the $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 salt: instead of a gradual monotonic decrease, the TEP shows a prominent sign-change before vanishing. Similar, although less pronounced features have been found in the other compound. The change in sign of the TEP is explained in terms of the two-fluid counterflow model, assuming a predominant role of one of the two anisotropic bands (namely, the electron-like one) in the superconducting pairing.

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