Superconductivity and local structural correlations in Ba_1-xK_xBiO₃

The doped perovskite BaBiO₃ exhibits a maximum superconducting transition temperature (T_c) of 34 K and was the first high-T_c oxide to be discovered, yet decades after its discovery the pairing mechanism is still debated, with strong electron-phonon coupling and bismuth valence/bond disproportionation possibly playing a role. Our recent diffuse x-ray scattering experiments and Monte Carlo modeling across its insulator-metal boundary revealed no evidence for either long- or short-range disproportionation, which resolves a major conundrum, as disproportionation and the related polaronic effects are likely not relevant for the metallic and superconducting states [1]. Instead, this work revealed nanoscale structural correlations that break inversion symmetry, which has far-reaching implications for the electronic physics, including the pairing mechanism. Here I will report our efforts to build on this work through diffuse scattering experiments at additional doping levels as well as charge transport and nonlinear magnetic response measurements of the normal and superconducting states.