Point contact spectroscopy and temperature dependence of resistivity of metallic sodium tungsten bronzes- role of optical phonons

Abstract

In this paper we report the results of electrical resistivity (1.5≤T≤300K) and point contact spectroscopy (PCS) measurements on single crystals of metallic sodium tungsten bronze with varying sodium content. We have shown that the electron-phonon coupling function as measured through PCS can explain quantitatively the large temperature dependence of resistivity ρ seen in these materials over the entire temperature range. The electron-phonon coupling function shows predominately large peaks for phonon frequency range of 30 meV≤ω≤100 meV which match well with the calculated optical phonons for WO₆ octahedron. The integrated electron-phonon coupling constant λ from this data is ≈0.25-0.45, depending on the Na content.