Electronic properties of correlated metals in the vicinity of a charge-order transition: Optical

N. DRICHKO,1,2 M. DRESSEL,1 C. A. KUNTSCHER,1,* A. PASHKIN,1,* A. GRECO,3 J. MERINO,4 AND J. SCHLUETER5

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 2006 vol. 74 p. 2351211 - 23512111

0163-1829

The infrared spectra of the quasi-two-dimensional organic conductors -BEDT-TTF2MHgSCN4 M=NH4, Rb, Tl were measured in the range from 50 to 7000 cm−1 down to low temperatures in order to explorethe influence of electronic correlations in quarter-filled metals. The interpretation of electronic spectra wasconfirmed by measurements of pressure dependent reflectance of -BEDT-TTF2KHgSCN4 at T=300 K.The signatures of charge order fluctuations become more pronounced when going from the NH4 salt to Rb andfurther to Tl compounds. On reducing the temperature, the metallic character of the optical response in theNH4 and Rb salts increases, and the effective mass diminishes. For the Tl compound, clear signatures of chargeorder are found albeit the metallic properties still dominate. From the temperature dependence of the electronicscattering rate the crossover temperature is estimated below which the coherent charge carriers response setsin. The observations are in excellent agreement with recent theoretical predictions for a quarter-filled metallicsystem close to charge order.