J. Phys. IV France
Volume 114, April 2004
Page(s) 289 - 290

J. Phys. IV France
114 (2004) 289
DOI: 10.1051/jp4:2004114061

Optical studies of $\kappa$-(ET) 2Cu[ N(CN) 2] Br 0.85Cl 0.15

J. Barz1, M. Dumm1, 1, M. Dressel1, C. Mézière2 and P. Batail2

1  Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
2  Laboratoire CIMI, FRE 2447 CNRS-Université d'Angers, Bât. K, UFR Sciences, 2 Bd. Lavoisier, 49045 Angers, France

The low-temperature ground states of the quasi two-dimensional layered organic charge transfer salts $\kappa$-(ET) 2Cu[ N(CN) 2] Br 1-xCl x are known to be strongly dependent on the Br/Cl content of the anions. At low temperatures, pure Cl compounds undergo a phase transition into an antiferromagnetic ground state while the pure Br compound is a organic superconductor. Here we present polarized infrared reflectivity measurements on the compound with 85% bromine and 15% chlorine. Our measurements were performed within the highly conducting a-c plane. From room temperature down to 90 K, we observe the typical signatures of a semiconductor in our spectra. When the sample is cooled down further, a significant amount of spectral weight is shifted towards lower frequencies. At 6 K, a Drude-like optical conductivity is observed in the far infrared Key words. charge-transfer salts - organic superconductors - optical properties.

© EDP Sciences 2004