Anisotropic electrodynamics of low dimensional metals: Optical studies of (TMTSF)₂ClO₄

Abstract

Optical experiments are reported for the metallic state of the linear chain compound (TMTSF)₂ClO₄. For the electric field polarized both along the highly (a) and intermediately (b′) conducting directions, a zero energy (ZE) mode and a finite energy mode (FE) are observed. The large anisotropy in the spectral weight of the FE mode is consistent with the band structure, however the spectral weight of the ZE mode is surprisingly isotropic. In the least conducting (c ^*) direction, the low frequency optical conductivity along with the dc conductivity indicate the presence of a (small) Drude component only at temperatures below 10 K. These observations provide evidence for a correlation induced semimetallic state, with a 3D to 2D crossover with increasing temperature.