J. Phys. IV France
Volume 12, Numéro 9, November 2002
Page(s) 57 - 60

J. Phys. IV France
12 (2002) Pr9-57
DOI: 10.1051/jp4:20020354

Charge ordering and superconductivity in $\alpha$-(BEDT-TTF) 2MHg(SCN) 4

M. Dressel1, N. Drichko1, 2, B. Salameh1, J. Thorns1, J. Schlueter3 and J. Merino4

1  I. Physikalisches Institut, Universitat Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
2  loffe Physico-Technical Institute, 194021 St. Petersburg, Russia
3  Material Science Divisions, Argonne National Laboratory, Argonne, IL 60439-4831, U.S.A.
4  Max-Planck-lnstitut fur Festkorperforschung, 70506 Stuttgart, Germany

In the optical spectra of the non-superconducting salt $\alpha$-(BEDT-TTF) 2KHg(SCN) 4 a strong feature appears at frequencies of about 200 cm -1 and temperatures below 200 K which indicates the opening of a pseudogap. This is in contrast to the superconducting $\alpha$-(BEDT-TTF) 2NH 4Hg(SCN) 4 whch exhlbits metallic-like optical properties down to 2 K. Based on exact diagonalisation calculations of the optical conductivity on an extended Hubbard model at quarter-filling we argue that the proximity of these salts to a charge ordering transition is responsible for the observed pseudogap. Our proposed scenario suggests that the different ground states, including superconductivity, are a consequence of the fluctuations associated with short range charge ordering which builds up close to the quantum phase transition.

© EDP Sciences 2002