Emergent granularity and pseudogap near the superconductor-insulator transition

Abstract

In two dimensions there is a direct superconductor-to-insulator quantum phase transition driven by increasing disorder. We elucidate, using a combination of inhomogeneous mean field theory and quantum Monte Carlo techniques, the nature of the phases and the mechanism of the transition. We make several testable predictions specifically for local spectroscopic probes. With increasing disorder, the system forms superconducting blobs on the scale of the coherence length embedded in an insulating matrix. In the superconducting state, the phases on the different blobs are coherent across the system whereas in the insulator long range phase coherence is disrupted by quantum fluctuations. As a consequence of this emergent granularity, we show that the single-particle energy gap in the density of states survives across the transition, but coherence peaks exist only in the superconductor. A characteristic pseudogap persists above the critical disorder and critical temperature, in contrast to conventional theories. Surprisingly, the insulator has a two-particle gap scale that vanishes at the SIT, despite a robust single-particle gap.

11 pages, 14 figures; proceedings of 14th International Conference on Transport in Interacting Disordered Systems (TIDS-14), 5-8 September 2011, Acre, Israel

References in corpus (6)

• Localization of preformed Cooper-pairs in disordered superconductors
• Nature of the superconductor-insulator transition in disordered superconductors
• Single and two-particle energy gaps across the disorder-driven superconductor-insulator transition
• Phase diagram of electrostatically doped Strontium Titanate (SrTiO3)
• Island formation in disordered superconducting thin films at finite magnetic fields
• Magnetic Field Tuned Quantum Phase Transition in the Insulating Regime of Ultrathin Amorphous Bi Films

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• Confinement of superconducting fluctuations due to emergent electronic inhomogeneities
• Direct evidence for Cooper pairing without a spectral gap in a disordered superconductor above $T_C$
• Stripe-like nanoscale structural phase separation and optimal inhomogeneity in superconducting BaPb${}_{1-x}$Bi${}_x$O${}_3$
• Global critical temperature in inhomogeneous superconductors induced by multifractality
• Enhanced, phase coherent, multifractal-like, two-dimensional superconductivity
• Superconductivity at the three-dimensional Anderson metal-insulator transition
• Effect of the Anomalous Diffusion of Fluctuating Cooper Pairs in the Density of States of Superconducting NbN Thin Films