Imaging how fluctuations destroy superconductivity in two dimensions

Abstract: Two-dimensional superconductors are model systems for thermal and quantum fluctuations. Key questions persist: whether existing models quantitatively describe the destruction of superconductivity, and whether an intermediate "anomalous metal state" represents a new phase of matter. We use scanning magnetic susceptibility to directly image the local phase stiffness, a thermodynamic measure of superconducting order, in gate-tunable Josephson junction arrays, a model two-dimensional superconductor. Across a broad range of carrier densities, we find that the superconducting critical temperature and phase stiffness are suppressed more strongly than expected from thermal fluctuations alone. At low carrier densities, we find that anomalous metal transport and large-scale spatial inhomogeneity emerge together. These results indicate that quantum fluctuations suppress superconductivity and that anomalous metal behavior emerges from phase slips in spatially disordered regions.