Point-contact spectroscopy of single crystalLa0.75Sr0.25MnO3and resistivity due to electron-phonon interaction

Abstract

In this paper we report point-contact spectroscopy (PCS) measurements on single crystals of metallic ${\mathrm{La}}_{0.75}{\mathrm{Sr}}_{0.25}{\mathrm{MnO}}_{3}.$ The electron-phonon coupling function as obtained from the PCS shows large peaks for phonon frequencies $20 \mathrm{meV}<~\ensuremath{\omega}<~100 \mathrm{meV}.$ This leads to a rather large electron-phonon coupling constant $\ensuremath{\lambda}\ensuremath{\simeq}1.2.$ We have shown that a sizable fraction of the total resistivity in the temperature range $T<~{0.4T}_{c}$ can be of phononic origin and can be explained using the experimentally observed electron-phonon coupling function. As $\stackrel{\ensuremath{\rightarrow}}{T}{T}_{c},$ extra contribution to resistivity arising from spins dominate. We find that the magnetoresistance vanishes in the temperature range $T<~{0.4T}_{c},$ where the predominant contribution to $\ensuremath{\rho}$ arises from phonons. We have also performed PCS in 6 T magnetic field. The resistivity calculated from the spectrum at 6 T does not differ appreciably from that calculated at 0 T. Our experiment has been validated by a similar experiment on a nonmagnetic perovskite oxide system, ${\mathrm{Na}}_{0.9}{\mathrm{WO}}_{3}.$