Unconventional pairing in bipolaronic theories

TL;DR

This paper uses a numerically exact quantum Monte Carlo method to study bipolaron binding, effective mass, and pairing symmetries in electron-phonon systems relevant to cuprate superconductivity.

Contribution

It introduces an efficient CTQMC algorithm to analyze bipolarons with arbitrary interactions, revealing properties of singlet and triplet pairs and extending to d-symmetry.

Findings

First analysis of effective mass and binding energies of bipolarons

Demonstrates the algorithm's efficiency for various pairing symmetries

Provides insights into unconventional pairing mechanisms

Abstract

Various mechanisms have been put forward for cuprate superconductivity, which fit largely into two camps: spin-fluctuation and electron-phonon (el-ph) mechanisms. However, in spite of a large effort, electron-phonon interactions are not fully understood away from clearly defined limits. To this end, we use a numerically exact algorithm to simulate the binding of bipolarons. We present the results of a continuous-time quantum Monte-Carlo (CTQMC) algorithm on a tight-binding lattice, for bipolarons with arbitrary interaction range in the presence of strong coulomb repulsion. The algorithm is sufficiently efficient that we can discuss properties of bipolarons with various pairing symmetries. We investigate the effective mass and binding energies of singlet and triplet real-space bipolarons for the first time, and discuss the extensions necessary to investigate $d$-symmetric pairs.