The crucial role of SSH interactions in the bismuthate superconductors Bi_1-xK_xBiO₃: A hybrid Monte Carlo study

Electron-phonon interactions can give rise to non-trivial emergent phenomena in quantum materials. For example, it is hypothesized that electron-phonon interactions are responsible for establishing the temperature-doping phase diagram of the bismuthate Bi_1-xK_xBiO₃ (BKBO) family of high-temperature superconductors. The precise nature of the interaction, however, is debated. In this work, we study a three dimensional Su-Schrieffer-Heeger (SSH) model that we believe captures the most important features of the electron-phonon coupling mechanism in BKBO. Using model parameters based on ab initio calculations, we simulate our SSH model using a novel Hybrid Monte Carlo (HMC) method, allowing us to reach system sizes a full order of magnitude larger than previously possible. Focusing first on the half-filled case, we observe the formation of charge order with a critical temperature between 1150 - 1250 K. This result is in qualitative and approximate quantitative agreement with experimental results reporting analogous charge formation between 800 - 900 K in BKBO samples. We also present initial results showing enhanced pairing correlations upon doping, consistent with the emergence of high-temperature superconductivity in BKBO.