Green's function of fully anharmonic lattice vibration

TL;DR

This paper derives a comprehensive Green's function for fully anharmonic lattice vibrations, revealing spectral and relaxation properties relevant to superconductivity in complex oxides.

Contribution

It introduces a general expression for the Green's function of fully anharmonic lattice vibrations, incorporating self-energy, vertex corrections, and normalization within second-order perturbation theory.

Findings

Spectral function characteristics vary from weakly anharmonic to double-well potentials.

Calculated NMR relaxation rates due to two-phonon Raman processes.

Provides insights into rattling motion coupled with conduction electrons.

Abstract

Motivated by the discovery of superconductivity in beta-pyrochlore oxides, we study property of rattling motion coupled with conduction electrons. We derive the general expression of the Green's function of fully anharmonic lattice vibration within the accuracy of the second order perturbation of electron-ion interaction by introducing self-energy, vertex-correction, and normalization factor for each transition. Using the expression, we discuss the characteristic properties of the spectral function in the entire range from weakly anharmonic potential to double-well case, and calculate NMR relaxation rate due to the two phonon Raman process.