Bond Bipolarons: Sign-free Monte Carlo Approach

TL;DR

This paper introduces sign-free Monte Carlo algorithms for studying bond bipolarons, revealing insights into their size, mass, and implications for high-temperature superconductivity.

Contribution

The authors develop efficient sign-free Monte Carlo methods for bond bipolaron models, enabling detailed analysis of their properties and potential role in superconductivity.

Findings

Bipolarons can be efficiently simulated using the new algorithms.

Results indicate a balance between bipolaron size and mass affects superconductivity.

On-site repulsion may promote s-wave superconductivity contrary to previous beliefs.

Abstract

Polarons originating from phonon displacement modulated hopping have relatively light masses and, thus, are of significant current interest as candidates for bipolaron mechanism of high-temperature superconductivity [Phys. Rev. Lett. {\bf 121}, 247001 (2018)]. We observe that the bond model, when the dominant coupling comes from atomic vibrations on lattice bonds, can be solved by efficient sign-free Monte Carlo methods based on the path-integral formulation of the particle sector in combination with either the (real-space) diagrammatic or Fock-path-integral representation of the phonon sector. We introduce the corresponding algorithms and provide illustrative results for bipolarons in two dimensions. The results suggest that the route towards high-temperature superconductivity (if any) in the multiparametric space of the model lies between the Scylla of large size of moderately light bipolarons and Charybdis of large mass of compact bipolarons. As a result, on-site repulsion is helping $s$-wave superconductivity in sharp contrast with existing expectations.