Confinement of superconducting fluctuations due to emergent electronic inhomogeneities

Abstract

The microscopic nature of an insulating state in the vicinity of a superconducting state, in the presence of disorder, is a hotly debated question. While the simplest scenario proposes that Coulomb interactions destroy the Cooper pairs at the transition, leading to localization of single electrons, an alternate possibility supported by experimental observations suggests that Cooper pairs instead directly localize. The question of the homogeneity, granularity, or possibly glassiness of the material on the verge of this transition is intimately related to this fundamental issue. Here, by combining macroscopic and nano-scale studies of superconducting ultrathin NbN films, we reveal nanoscopic electronic inhomogeneities that emerge when the film thickness is reduced. In addition, while thicker films display a purely two-dimensional behaviour in the superconducting fluctuations, we demonstrate a zero-dimensional regime for the thinner samples precisely on the scale of the inhomogeneities. Such behavior is somehow intermediate between the Fermi and Bose insulator paradigms and calls for further investigation to understand the way Cooper pairs continuously evolve from a bound state of fermionic objects into localized bosonic entities.

29 pages 9 figures

References in corpus (4)

• Localization of preformed Cooper-pairs in disordered superconductors
• Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition
• Eigenfunction fractality and pseudogap state near superconductor-insulator transition
• Fluctuation spectroscopy of granularity in superconducting structures

Cited by in corpus (25)

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• Spectroscopic evidence for strong correlations between local superconducting gap and local Altshuler-Aronov density-of-states suppression in ultrathin NbN films
• Optical signatures of the superconducting Goldstone mode in granular aluminum: experiments and theory
• Magnetic field induced emergent inhomogeneity in a superconducting film with weak and homogeneous disorder
• Broadening of the Berezinskii-Kosterlitz-Thouless transition by correlated disorder
• Substrate mediated nitridation of niobium into superconducting Nb2N thin films for phase slip study
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• Probing the Berezinskii-Kosterlitz-Thouless vortex unbinding transition in two-dimensional superconductors using local noise magnetometry
• Ultrahigh-inductance materials from spinodal decomposition
• Magnetic field-tuned superconductor/insulator transition in TiN nanostrips
• The paraconductivity of granular Al-films at high reduced temperatures and magnetic fields
• Effect of Coulomb Interaction and Disorder on Density of States in Conventional Superconductors
• Structural properties and magnetoresistance of La${}_{1.952}$Sr${}_{0.048}$CuO${}_4$ thin films
• Effect of the Anomalous Diffusion of Fluctuating Cooper Pairs in the Density of States of Superconducting NbN Thin Films
• On the dilemma between percolation processes and fluctuating pairs as the origin of the enhanced conductivity above the superconducting transition in cuprates
• Understanding and enhancing superconductivity in FeSe/STO by quantum size effects
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• Phenomenological model for the third-harmonic magnetic response of superconductors: application to Sr${}_2$RuO${}_4$
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• Superfluid response of two-dimensional filamentary superconductors
• Advanced approach of superconducting gap function extraction from tunneling experiments