Optical properties of monophosphate tungsten bronze P_4W_14O_50
Abstract
We report the polarized optical reflectance of P_4W_14O_50, the only charge density wave (CDW) superconductor in the monophosphate tungsten bronze family. P_4W_14O_50 has two CDW transitions at 188 and 60 K, and a superconducting transition at ~ 0.3 K. The 300 K ab-plane spectra display high reflectance with weak phonons in the infrared, an anisotropic intra-t_2g d arrow d excitation ( ~10000 cm-1), and a nearly isotropic O p arrow W d charge transfer transition ( ~35000 cm-1). In contrast, the interlayer spectrum shows low reflectance and strong vibrational modes, indicating non-metallic transport along c. The variable temperature ab-plane spectra clearly show a suppression of the optical conductivity along the b-axis below 140 K, giving rise to charge localization and anisotropic CDW gap formation at ~ 1400 cm-1. Although there is an important redistribution of oscillator strength below 100 K, the spectral weight is largely conserved below the plasma frequency. The ab-plane phonons become well-resolved in the CDW states, due to reduced screening. We also compare the spectra of P_4W_14O_50 with the other CDW superconductors.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2002
- Bibcode:
- 2002APS..MART13003Z