Indications of electronic correlations in the 1/5-filled two-dimensional conductor

N. DRICHKO,1,2 K. PETUKHOV,1 M. DRESSEL,1 O. BOGDANOVA,3 E. ZHILYAEVA,3 R. LYUBOVSKAYA,3 A. GRECO,4 AND J. MERINO5,*

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 2005 vol. 72 p. 245241 - 245247

0163-1829

The polarized reflectivity of -BEDO-TTF5CsHgSCN42 is studied in the infrared range between60 cm−1 and 6000 cm−1 from room temperature down to 6 K. Already at T=300 K a pseudogap in the opticalconductivity is present at about 150 cm−1; the corresponding maximum in the spectrum shifts to lower frequenciesas the temperature decreases. A robust Drude component is observed in the spectra which is muchlarger than comparable quarter-filled compounds; we ascribe it to the larger fraction of charge carriers associatedwith the 1/5-filling of the conduction band. This observation is corroborated by exact diagonalizationcalculations on an extended Hubbard model on a square lattice for different fillings. A broad band at 4500 cm−1which appears for the electric field polarized parallel to the stacks of the BEDO-TTF molecules is associatedwith structural modulations in the stacks; these modulations lead to a rise of the dc and microwave resistivityin 100 to 30 K temperature range.