Experimental Evidence for a Collective Insulating State in Two-Dimensional Superconductors

Sambandamurthy, G.; Engel, L. W.; Johansson, Andreas; Peled, E.; Shahar, D.

doi:10.1103/physrevlett.94.017003

Cited by 119 publications

(146 citation statements)

References 20 publications

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“…2. At high magnetic fields the films on both sides of the SIT show large negative magnetoresistance [21,44,52,53,57,55,45]. It is important that such behavior was observed even in films characterized by a very high activation energy.…”

Section: Experimental Results On S-i Transitionsmentioning

confidence: 99%

Fractal superconductivity near localization threshold

Фейгельман¹,

Ioffe²,

Kravtsov³

et al. 2010

Annals of Physics

238

360

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We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk "poor conductors" in which Fermi energy E F is located in the region of localized states not so far from the Anderson mobility edge E c . We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model.Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems.We identify three distinct phases: 'critical' superconductive state formed at E F = E c , superconducting state with a strong pseudogap, realized due to pairing of weakly localized electrons and insulating state realized at E F still deeper inside localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gaped state is the presence of two independent energy scales: superconducting gap ∆, that is due to many-body correlations and a new "pseudogap" energy scale ∆ P which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive T c . Two gap nature of the pseudogapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudogaped superconducting state demonstrates anomalous behavior of the optical spectral weight. The insulating state is realized due to presence of local pairing gap but without superconducting correlations; it is characterized by a hard insulating gap in the density of single electrons and by purely activated low-temperature resistivity ln R(T ) ∼ 1/T .Based on these results we propose a new "pseudospin" scenario of superconductorinsulator transition and argue that it is realized in a particular class of disordered superconducting films. We conclude by the discussion of the experimental predictions of the theory and the theoretical issues that remain unsolved.

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Section: Experimental Results On S-i Transitionsmentioning

confidence: 99%

Fractal superconductivity near localization threshold

Фейгельман¹,

Ioffe²,

Kravtsov³

et al. 2010

Annals of Physics

238

360

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show abstract

“…One of the central issues in the 2D SIT, is the nature of conduction in the insulating state of B tuned SIT, where at low-T resistance per square (R ) become very high 17,18 . In several 2D disordered superconductors, such as thin MoGe films 19 , Ta films 20 , amorphous Bi films 21 (R ) become independent of T as the lowest T is approached.…”

Section: Quantum Phase Transition (Qpt)mentioning

confidence: 99%

Finite-size effects in amorphous indium oxide

et al. 2016

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We study the low temperature magneto-transport properties of several highly disordered amorphous Indium oxide(a:InO) samples. Simultaneously fabricated devices comprising a 2-dimensional (2D) film and 10 µm long wires of different widths were measured to investigate the effect of size as we approach the 1D limit, which is around 4 times the correlation length, and happens to be around 100 nm for a:InO. The film and the wires showed magnetic field (B) induced superconductor to insulator transition (SIT). In the superconducting side, the resistance increased with decrease in wire width, whereas, an opposite trend is observed in the insulating side. We find that this effect can be explained in light of charge-vortex duality picture of the SIT. Resistance of the 2D film follows an activated behavior over the temperature (T ), whereas, the wires show a crossover from the high-T activated to a T -independent behavior. At high temperature regime the wires' resistance follow the film's until they deviate and became independent of T . We find that temperature at which this deviation occurs evolve with magnetic field and the width of the wire, which show the effect of finite size on the transport.

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“…Disordered films with superconducting correlations host an amazing variety of interesting phenomena such as superconductor-insulator transitions tuned by disorder or an external magnetic field, with rather unusual transport properties [1][2][3][4][5][6][7][8][9][10] . These phenomena led to a lot of interesting theoretical work [11][12][13][14][15][16][17][18] , which were to a great extent spurred by an experimental feature of many strongly disordered films with superconducting correlations -a giant magnetoresistance peak -for which a full theoretical understanding is still lacking.…”

mentioning

confidence: 99%

Two-component Coulomb glass in insulators with a local attraction

et al. 2012

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Motivated by evidence of local electron-electron attraction in experiments on disordered insulating films, we propose a new two-component Coulomb glass model that combines strong disorder and long-range Coulomb repulsion with the additional possibility of local pockets of a short-range interelectron attraction. This model hosts a variety of interesting phenomena, in particular a crucial modification of the Coulomb gap previously believed to be universal. Tuning the short-range interaction to be repulsive, we find non-monotonic humps in the density of states within the Coulomb gap. We further study variable-range hopping transport in such systems by extending the standard resistor network approach to include the motion of both single electrons and local pairs. In certain parameter regimes the competition between these two types of carriers results in a distinct peak in resistance as a function of the local attraction strength, which can be tuned by a magnetic field.

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Experimental Evidence for a Collective Insulating State in Two-Dimensional Superconductors

Cited by 119 publications

References 20 publications

Fractal superconductivity near localization threshold

Fractal superconductivity near localization threshold

Finite-size effects in amorphous indium oxide

Two-component Coulomb glass in insulators with a local attraction

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