Superfluid transition temperature of bond bipolarons with Coulomb interaction

Using numerically exact diagrammatic Monte Carlo simulations in the two-electron (single-bipolaron) sector, we explore the impact of long-range Coulomb repulsion on the dilute-limit Berezinskii-Kosterlitz-Thouless transition temperature T c of bipolarons on a two-dimensional square lattice. We study the bond Su-Schrieffer-Heeger model, in which bond phonons modulate the electron hopping. In the absence of long-range repulsion, this model was shown to support small, light bipolarons with a comparatively high transition temperature C. Zhang, J. Sous, D. R. Reichman, M. Berciu, A. J. Millis, N. V. Prokof’ev, and B. V. Svistunov, Bipolaronic high-temperature superconductivity, . Here, we find that long-range Coulomb repulsion suppresses the optimal T c but leaves it appreciable over a broad parameter window, including the adiabatic regime ω / t = 0.5 at a representative Coulomb strength V = U / 10 (with U the on-site repulsion). Our results provide controlled single-bipolaron inputs for dilute-limit T c estimates in the presence of long-range repulsion.