J. Phys. IV France
Volume 114, April 2004
Page(s) 217 - 221

J. Phys. IV France
114 (2004) 217
DOI: 10.1051/jp4:2004114047

Comparative magnetotransport and $T_{\rm c}$ measurements under pressure on $\kappa$-(BEDT-TTF) 2Cu(NCS) 2

A.-K. Klehe1, 1, T. Biggs1, T. Tomita2, J.S. Schilling2, A.M. Kini3 and J.A. Schlueter3

1  Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU, UK
2  Dept. of Physics, Washington University, C.B 1105. One Brookings Drive, St. Louis, MO 63130, USA
3  Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Il 60439, USA

$\kappa$-(BEDT-TTF) 2Cu(NCS) 2 is one of the best characterized organic superconductors. The resemblance of its pressure-temperature phase diagram to that of the carrier-density-temperature phase diagram in cuprate superconductors has frequently been taken as evidence for similar interaction mechanisms governing superconductivity, even though direct evidence for a correlation between carrier density and T $_{\rm c}$ in organic superconductors had been missing. We have performed and compared several magnetoresistive as well as ac-susceptibility measurements under pressure on single crystals of $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 with different isotopical composition. The isotopical composition of $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 is irrelevant to the pressure dependence of the superconducting state. In general, pressure on $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 is seen to decrease T $_{\rm c}$ and to increase the quasi 2-dimensional Fermi surface area. The exact pressure dependence, however, seems to be strongly influenced by the pressure technique used. However, the apparent divergence of the reported pressure dependences in $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 converges into one dependence of T $_{\rm c}$ against the carrier concentration of the quasi 2-dimensional Fermi surface. Pressure in $\kappa$-(BEDT-TTF) 2Cu(NCS) 2 is seen to transfer carriers from the quasi 1-dimensional to the quasi 2-dimensional Fermi surface section. The present results point to a strong correlation between T $_{\rm c}$ and the quasi 2-dimensional carrier concentration in this organic superconductor. Key words. Pressure - superconducting transition temperature - carrier concentration - organic molecular metal

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