Optical Studies of Quasi-Two-Dimensional Charge Density Wave Compounds (PO_2)_4(WO_3)_2m (m=4,6)
Abstract
We report the optical properties of quasi-two-dimensional charge density wave (CDW) compounds (PO_2)_4(WO_3)_2m (m=4, 6). CDW transitions occur at T_c1 =80 K and T_c2 =52 K for the m=4 compound, and T_c1 =120 K and T_c2 =62 K for the m=6 material. The far and middle infrared spectra of m=4 and m=6 show that both compounds are highly reflective and have a rather isotropic response in the conducting ab plane, whereas electronic excitations in the near-infrared and visible range are strongly anisotropic at room temperature. The optical conductivity spectrum of the m=4 material has a strong absorption peak in the infrared range at all temperatures down to 10 K. On the other hand, the spectrum of the m=6 compound in the conducting ab plane exhibits a metallic response at room temperature and a clear CDW gap in the middle infrared below T_c1 (120 K). In addition, phase phonons show up in the CDW states for the m=6 compound, whereas no phonons are observed for the m=4 material. We discuss the results in terms of CDW and dimensionality effects on the electrodynamics of these Q2D monophosphate tungsten bronzes.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2001
- Bibcode:
- 2001APS..MARC16018Z