Giant enhancement of anisotropy by electron-phonon interaction

TL;DR

This paper demonstrates that electron-phonon interactions can exponentially enhance anisotropy in polaron bands, significantly affecting material properties and potentially explaining variations in high-temperature superconductors.

Contribution

It introduces a model showing exponential anisotropy enhancement due to electron-phonon coupling and predicts isotope effects on mass anisotropy, with polaron masses calculated via Quantum Monte Carlo.

Findings

Anisotropy of polaron band can be exponentially large.

Anisotropy is highly sensitive to small changes in coupling.

Predicted isotope effect on mass anisotropy.

Abstract

Anisotropic electron-phonon interaction is shown to lead to the anisotropic polaron effect. The resulting anisotropy of the polaron band is an exponential function of the electron-phonon coupling and might be as big as $10^3$. This also makes anisotropy very sensitive to small changes of coupling and implies wide variations of anisotropy among compounds of similar structure. The isotope effect on mass anisotropy is predicted. Polaron masses are obtained by an exact Quantum Monte Carlo method. Implications for high-temperature superconductors are briefly discussed.