J. Phys. IV France
Volume 114, April 2004
Page(s) 227 - 231

J. Phys. IV France
114 (2004) 227
DOI: 10.1051/jp4:2004114049

Spin-liquid behavior and superconductivity in $\kappa
$ -(BEDT-TTF) 2X: The role of uniaxial strain

M. Maesato1, Y. Shimizu1, 2, T. Ishikawa1, G. Saito1, K. Miyagawa2, 3 and K. Kanoda2, 3

1  Division of Chemistry, Graduate School of Science, Kyoto University, Oiwaketyo, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
2  Department of Applied Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
3  CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012, Japan

We have examined the relationship between the anisotropy of the triangular lattice and the electronic states of $\kappa
$ -(BEDT-TTF) 2X. We have found the spin-liquid behavior in a Mott insulator $\kappa
$-(BEDT-TTF) 2Cu 2(CN) 3 which has nearly regular triangular lattice. The 1H-NMR study confirmed that this compound shows no magnetic ordering down to 32mK, indicating the significant role of the large spin frustration. The uniaxial compressive strain along the b- or c-axes induced superconductivity in close proximity to the spin-liquid phase. Further, its transition temperature TC was increased under the strains. The enhancement of TC has been interpreted by the effect of the reduction of spin frustration by the strains. The TC of $\kappa
$-(BEDT-TTF) 2X and its response to the uniaxial strain have been discussed in terms of the anisotropy of the triangular lattice and electron correlation. Key words. Spin-liquid, Superconductivity, Mott insurator, Uniaxial strain.

© EDP Sciences 2004