J. Phys. IV France 12 (2002) Pr9-57
Charge ordering and superconductivity in -(BEDT-TTF) 2MHg(SCN) 4M. 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 -(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 -(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