Bolometric infrared spectra of (TaSe4)2I

Abstract

Low-temperature infrared absorption spectra of the charge-density-wave conductor (${\mathrm{TaSe}}_4$ ${)}_2$I, were taken between 230 and 4000 ${\mathrm{cm}}^{\mathrm{-}1}$ by using the sample as a bolometric self-detector. Absorption edges observed for light polarized parallel and perpendicular to the conducting axis are broad, presumably due to iodine disorder. The edge observed with parallel polarization is weaker, more temperature dependent, and at lower energy than that observed for perpendicular polarization. The anisotropy is interpreted in terms of a two-band model incorporating interchain coupling, but the strong temperature dependence of the smaller gap is difficult to reconcile with the measured activation energy. No absorption features that could be correlated with midgap soliton states were observed.