SPA Colloquium: Martin Greven (UMN)

Title: New developments in oxide superconductors – the role of inherent inhomogeneity

Abstract: Superconductivity has been a major scientific topic for more than a century, yet in many important materials the emergence of this macroscopic quantum phenomenon remains poorly understood. Recent charge transport and thermodynamic measurements have revealed unusual yet universal superconducting fluctuation behavior in four well-known families of perovskite oxides – strontium titanate, strontium ruthenate, the bismuthates, and the cuprates – for which the superconducting pairing mechanisms are thought to differ. Complementary neutron and x-ray scattering measurements support the notion that both the electronic and structural order parameters in these materials couple to an underlying “hidden” inhomogeneity that is distinct from conventional point disorder, and that rare-region effects play a prominent role. These findings have far-reaching implications for the interpretation of electronic properties of perovskites in general, including thin films and heterostructures. In the case of the cuprates, inherent inhomogeneity constitutes a pivotal part of a robust phenomenological model that comprehensively captures hitherto elusive properties of the normal and superconducting states.