Steve Johnston, UT Knoxville, Wed, April 13, 2022, 1:25pm – 2:25pm
The bismuthate family of superconductors exhibits high-temperature superconductivity proximate to a charge-ordered insulating phase. However, despite decades of research, the community has yet to identify the pairing mechanism in these materials. Leading proposals include correlation-enhanced electron-phonon interactions, negative-U centers arising from charge disproportionation, or polaronic scenarios. In this talk, I will discuss recent work that sheds new light on this long-standing problem and points to the crucial role of Su-Schrieffer-Heeger (SSH)-like interactions and possible polaronic physics [1-4]. I will first summarize recently available ARPES and core-level photoemission data., which rules out correlation-driven mechanisms. I will then discuss our recent quantum Monte Carlo studies [2-4], solving a multi-orbital model for the bismuthates that explicitly accounts for the SSH-like interaction arising from the modulation of the Bi-O overlap integrals. Using a state-of-the-art hybrid MC implementation, we treat this model on large three-dimensional lattices of upwards of 4000's atoms [4]. Our model captures the charge-ordered state near half-filling with a critical temperature in approximate quantitative agreement with experimental results. Upon doping, it also predicts enhanced pairing correlations and polaronic liquid-like conditions consistent with the superconducting state observed in the actual materials. Our results point to the crucial role of the SSH-like electron-phonon interactions in this family of superconductors.