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 $P(\mathbf{r},\omega)$, compressibility $\kappa(\mathbf{r})$, and diamagnetic susceptibility $\chi(\mathbf{r})$. 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. $P(\mathbf{r},\omega)$, 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 $\kappa(\mathbf{r})$. We investigate the signatures of quantum fluctuations in the evolution of $\kappa(\mathbf{r})$ and $\chi(\mathbf{r})$ across the SIT, distinct from thermal fluctuations. We discuss the experimental implications of our results for scanning Josephson spectroscopy, compressibility, and scanning SQUID measurements.