Optical properties of hexamethylene-tetraselenafulvalinium tetracyanoquinodi-methanide (HMTSF-TCNQ)

Abstract

Polarized single crystal reflectance studies of HMTSF-TCNQ are presented. One reflectance component perpendicular to the highly conducting direction is flat and rather low, the other shows a transition at ω = 16000 cm⁻¹, much stronger than usually seen in conducting TCNQ salts. The highly conducting direction displays a plasma edge. An analysis yields a plasmon frequency ω_p = 7400 cm⁻¹, an inverse life time λ = 1300 cm⁻¹, and an optical mass m^* = 1.9 mo. The low-temperature reflectance gives ω_p = 8200 cm⁻¹ and a 2.4 times longer lifetime, consistent with the temperature dependence of the do conductivity.