Charge ordering and superconductivity in $\alpha$-(BEDT-TTF)$_2M$Hg(SCN)$_4$

M. Dressel; N. Drichko; B. Salameh; J. Thorns; J. Schlueter; J. Merino

doi:doi:10.1051/jp4:20020354

Issue		J. Phys. IV France Volume 12, Number 9, November 2002


Page(s)		57 - 60
DOI		https://doi.org/10.1051/jp4:20020354

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. Drichko^{1, 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

Abstract
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.

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

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