Anharmonic theory of superconductivity and its applications to emerging quantum materials

TL;DR

This paper reviews recent theoretical advances on how anharmonic effects influence superconductivity, emphasizing their importance in emerging quantum materials and discussing potential experimental and computational approaches.

Contribution

It introduces a unified theoretical framework combining anharmonic effects with established superconductivity theories and applies it to novel quantum materials.

Findings

Anharmonic decoherence significantly impacts superconducting properties.

Universal properties of anharmonic damping are identified.

Applications to hydrides, ferroelectrics, and charge density wave systems are demonstrated.

Abstract

The role of anharmonicity on superconductivity has often been disregarded in the past. Recently, it has been recognized that anharmonic decoherence could play a fundamental role in determining the superconducting properties (electron-phonon coupling, critical temperature, etc) of a large class of materials, including systems close to structural soft-mode instabilities, amorphous solids and metals under extreme high-pressure conditions. Here, we review recent theoretical progress on the role of anharmonic effects, and in particular certain universal properties of anharmonic damping, on superconductivity. Our focus regards the combination of microscopic-agnostic effective theories for bosonic mediators with the well-established BCS theory and Migdal-Eliashberg theory for superconductivity. We discuss in detail the theoretical frameworks, their possible implementation within first-principles methods, and the experimental probes for anharmonic decoherence. Finally, we present several concrete applications to emerging quantum materials, including hydrides, ferroelectrics and systems with charge density wave instabilities.