Probing inhomogeneity in high-temperature superconductors
It is known that the high-temperature superconductors are strikingly inhomogeneous. I summarize here key results from recent theoretical and experimental studies of these materials, all involving their inhomogeneity as an important element. First, I present results on iron-based superconductors. Employing a phase-sensitive quasiparticle scattering interference-based technique optimized for disordered materials, the particular pairing symmetries of FeSe and LiFeAs are deduced from scanning tunneling microscopy (STM) experiments. Second, I report recent work on overdoped cuprates. Using STM, the emergence of an unusual "puddly" form of superconductivity in this regime is visualized, with gaps persisting even when superconductivity has disappeared, consistent with a model of superconducting puddles embedded in a metallic matrix. Finally, I show theoretical results showing how phase fluctuations can be detected via angle-resolved photoemission spectroscopy, and how the amount of inhomogeneity in the superfluid density of the cuprates can be estimated from these experiments.