Enhanced electron-phonon coupling near an electronic quantum phase transition

TL;DR

This paper presents a simple model showing that proximity to an electronic quantum phase transition can significantly enhance electron-phonon coupling, potentially leading to high-temperature phonon superconductors.

Contribution

It introduces a general model demonstrating how quantum phase transitions can cause anomalous phonon frequency increases and strong electron-phonon coupling.

Findings

Phonon frequency can be abnormally increased near a quantum phase transition.

Electron-phonon coupling strength is enhanced near the transition point.

Potential pathway for designing high-temperature phonon superconductors.

Abstract

I construct a simple model to demonstrate that when the many-electron quantum state of a material is near a quantum phase transition and the vibrational motion of a phonon explores the potential energy surface near the transition point, then an impenetrable barrier appears at the potential energy surface which restricts the phonon from crossing the transition point and abnormally increases the phonon frequency. The ensuing anomalous enhancement of the electron phonon coupling is general and independent of the specific nature of the electronic quantum phase transition. Understanding and modelling this strong electron-phonon coupling may potentially lead to the design of phonon superconductors with high critical temperatures by choosing their parameters appropriately near an electronic quantum phase transition.