In-plane quasi-isotropic organic superconductor di[bis(ethylenedithiolo) tetrathiafulvalene] bis(isothiocyanato) cuprate (I), (BEDT-TTF)[Cu(NCS)2]2: Polarized reflectance spectra

Abstract

Polarized reflectance spectra with polarizations parallel to the crystallographic $b$ and $c$ axes which lie on the two-dimensional conducting planes of a new ambient-pressure organic superconductor (BEDT-TTF) ${}_2{}^{}{}_{}{}^{}\left[\mathrm{C}\mathrm{u}{\mathrm{}\left(\mathrm{NCS}\right)\mathrm{}}_2\right]$ were measured over the range from 500 to 28 000 ${\mathrm{cm}}^{-1\mathrm{}}$ at room temperature. Plasma-edge-like dispersion with the minimum near 5000 ${\mathrm{cm}}^{-1\mathrm{}}$ was observed for both polarizations. The bandwidths of the superconductor evaluated in terms of the Drude model and the tight-binding approximation were found to be 0.73 eV in the $b$-axis direction and 0.40 eV in the $c$-axis direction, thereby indicating the quasi-isotropic nature of the optical charge transport in the $\mathrm{bc}$ plane.