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Single- and two-particle energy gaps across the disorder-driven superconductor–insulator transition

Abstract

The competition between superconductivity and localization raises profound questions in condensed-matter physics. In spite of decades of research, the mechanism of the superconductor–insulator transition and the nature of the insulator are not understood. We use quantum Monte Carlo simulations that treat, on an equal footing, inhomogeneous amplitude variations and phase fluctuations, a major advance over previous theories. We gain new microscopic insights and make testable predictions for local spectroscopic probes. The 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 superconductor–insulator transition, despite a robust single-particle gap.

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Figure 1: Energy and temperature scales across SIT.
Figure 2: The single-particle DOS.
Figure 3: Imaginary part of the dynamical pair susceptibility.
Figure 4: Local density of states (LDOS) N(R,ω), density n(R), and BdG pairing amplitude Δop(R) as a function of disorder strength for a montage of nine disorder realizations of 8×8lattices.
Figure 5: Emergent granularity.

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Acknowledgements

We gratefully acknowledge support from NSF DMR-0907275 (K.B.), US Department of Energy, Office of Basic Energy Sciences grant DOE DE-FG02-07ER46423 (N.T., Y.L.L.), NSF DMR-0706203 and NSF DMR-1006532 (M.R.), and computational support from the Ohio Supercomputing Center.

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K.B. and Y.L.L. performed the numerical calculations; M.R. and N.T. were responsible for the project planning; all authors contributed to the data analysis, discussions and writing.

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Correspondence to Nandini Trivedi.

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The authors declare no competing financial interests.

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Bouadim, K., Loh, Y., Randeria, M. et al. Single- and two-particle energy gaps across the disorder-driven superconductor–insulator transition. Nature Phys 7, 884–889 (2011). https://doi.org/10.1038/nphys2037

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