Anisotropic ab-plane optical response of the charge-density-wave superconductor P4W14O50 - art. no. 214519

摘要

We report the polarized optical reflectance of P4W14O50, the only charge-density-wave (CDW) superconductor in the monophosphate tungsten bronze family, over a wide frequency range. The 300-K infrared spectra are dominated by two-dimensional behavior: high reflectance with weak phonons in the conducting ab plane and low reflectance with strong vibrational modes along the interlayer direction. An anisotropic intra-t(2g)d-->d excitation (similar to10000 cm(-1)) reveals the "hidden" one-dimensional band structures in P4W14O50. 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 similar to1400 cm(-1). Although the oscillator strength is redistributed among the free-carrier response, the CDW gap absorption, and the d-->d transition in the density wave states, 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. Based upon these observations, P4W14O50 is another example of a superconductor with an unusual normal state. [References: 53]