Light Bipolarons Stabilized by Peierls Electron-Phonon Coupling

TL;DR

This paper demonstrates that strong Peierls electron-phonon coupling can produce light, stable bipolarons with unconventional properties, potentially enabling high-temperature superconductivity contrary to previous beliefs.

Contribution

It reveals that Peierls/Su-Schrieffer-Heeger interaction leads to light bipolarons with unique properties, challenging the notion that strong electron-phonon coupling always results in heavy polarons.

Findings

Light bipolarons are stable at strong coupling.

Bipolarons exhibit two low-energy bands resistant to Hubbard repulsion.

Unusual pair-hopping interaction influences superconducting properties.

Abstract

It is widely accepted that phonon-mediated high-temperature superconductivity is impossible at ambient pressure, because of the very large effective masses of polarons/bipolarons at strong electron-phonon coupling. Here we challenge this belief by showing that strongly bound yet very light bipolarons appear for strong Peierls/Su-Schrieffer-Heeger interaction. These bipolarons also exhibit many other unconventional properties, e.g. at strong coupling there are two low-energy bipolaron bands that are stable against strong on-site Hubbard repulsion. Using numerical simulations and analytical arguments, we show that these properties result from the specific form of the phonon-mediated interaction, which is of "pair-hopping" instead of regular density-density type. This unusual effective interaction is bound to have non-trivial consequences for the superconducting state expected to arise at finite carrier concentrations, and should favor a large critical temperature.