Two-Dimensional Band Structure of Organic Metals (BDT-TTP)2X (X=SbF6, AsF6) Studied by Polarized Reflection Spectroscopy

Abstract

Polarized reflectance spectra were measured on the conductive (010) plane of metallic (BDT-TTP) 2 X (X=SbF 6 , AsF 6 ) single crystals at room and low temperatures. Well-defined plasma edges appeared in both directions parallel (// a ) and perpendicular (⊥ a ) to the molecular stack, indicating two-dimensional band structures with a significant anisotropy. The intra- and inter-stack transfer integrals were estimated from the plasma frequencies in the framework of tight-binding model. Based on these transfer integrals, the energy dispersion, density of state, and Fermi surface were calculated. The Fermi surfaces of both compounds were open in the k c direction. The temperature dependence of the transfer integrals was determined by analyzing the low-temperature spectra. The intra-stack transfer integral increased by about 30% whereas the enhancement of inter-stack transfer integral was very weak. So the system became more anisotropic at low temperatures. The strongly appeared CH stretching mode in the ⊥ a s...