Electron Mass Enhancement due to Anharmonic Local Phonons

TL;DR

This paper investigates how anharmonic local phonons, or rattling, enhance electron effective mass by analyzing the anharmonic Holstein model with a Green's function approach, highlighting the interplay of quantum and rattling effects.

Contribution

It introduces a detailed analysis of electron mass enhancement due to anharmonic phonons using the Holstein model and Green's function method, emphasizing the role of zero-point energy.

Findings

Maximum electron mass enhancement occurs when zero-point energy matches potential barrier height.

Quantum and rattling effects cooperate to significantly increase electron effective mass.

The study provides insights into electron-rattling systems relevant for materials with cage-like structures.

Abstract

In order to understand how electron effective mass is enhanced by anharmonic local oscillation of an atom in a cage composed of other atoms, i.e., {\it rattling}, we analyze anharmonic Holstein model by using a Green's function method. Due to the evaluation of an electron mass enhancement factor $Z$, we find that $Z$ becomes maximum when zero-point energy is comparable with potential height at which the amplitude of oscillation is rapidly enlarged. Cooperation of such quantum and rattling effects is considered to be a key issue to explain the electron mass enhancement in electron-rattling systems.