Local spectroscopies across the superconductor-insulator transition

Abstract

We explore the manifestation of quantum fluctuations across the superconductor-insulator transition (SIT) in three different local measurements: the two-particle density of states P (r, ω), compressibility κ(r), and diamagnetic susceptibility χ(r). We perform Monte Carlo simulations on the 2D quantum Josephson junction array model and present local maps of these quantities as the system is tuned across the SIT. P (r, ω), obtained using Maximum Entropy analytic continuation techniques, shows strongly diminished zero-energy spectral weight in nearly-insulating islands, that also correlate with regions of suppressed κ(r). We investigate the signatures of quantum fluctuations in the evolution of κ(r) and χ(r) across the SIT, distinct from thermal fluctuations. We discuss the experimental implications of our results for scanning Josephson spectroscopy, compressibility, and scanning SQUID measurements. arXiv:1812.06954v3 [cond-mat.supr-con]

Superconductor–insulator transition in two-dimensional indium–indium-oxide composite

“…Quantum fluctuations of the phase of the superconducting order parameter control this QPT (11). On theoretical grounds, this approach is equivalent to a disordered array of superconducting islands coupled by Josephson junctions, where the amplitude fluctuations are ignored (12,13). Thus, applying the conventional picture to experimentally studied material systems is strongly influenced by the film's effective morphology.…”