Phase Fluctuations in a Strongly Disordered<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>s</mml:mi></mml:math>-Wave NbN Superconductor Close to the Metal-Insulator Transition

Mondal, Mintu; Kamlapure, Anand; Chand, Madhavi; Saraswat, Garima; Kumar, Sanjeev; Jesudasan, John; Benfatto, Lara; Tripathi, Vikram; Raychaudhuri, Pratap

doi:10.1103/physrevlett.106.047001

Cited by 184 publications

(233 citation statements)

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“…14 Moreover, the observation of a pseudogap in strongly disordered SC films [8][9][10][11][12][13] bears some resemblance to similar experimental findings in high-temperature superconductors [15][16][17] that may suggest a common mechanism in some regions of the phase diagram.…”

Section: Introductionmentioning

confidence: 64%

“…For a given disorder strength only few sites are close to this regime and their number decreases with increasing V 0 /t due to the decrease of SC islands. There are also few sites, as (10,5), where the SC order parameter reemerges at a large value of the disorder strength and stays finite over some range of V 0 . In the appendix the behavior of ∆ i and χ AA ii for all sites of the sample is analyzed in more detail.…”

Section: Real Space Structure Of Responsesmentioning

confidence: 99%

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Amplitude, density, and current correlations of strongly disordered superconductors

2015

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We investigate the disorder dependence of the static density, amplitude and current correlations within the attractive Hubbard model supplemented with on-site disorder. It is found that strong disorder favors a decoupling of density and amplitude correlations due to the formation of superconducting islands. This emergent granularity also induces an enhancement of the density correlations on the SC islands whereas amplitude fluctuations are most pronounced in the 'insulating' regions. While density and amplitude correlations are short-ranged at strong disorder we show that current correlations have a long-range tail due to the formation of percolative current paths in agreement with the constant behavior expected from the analysis of one-dimensional models.

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Section: Introductionmentioning

confidence: 64%

Section: Real Space Structure Of Responsesmentioning

confidence: 99%

Amplitude, density, and current correlations of strongly disordered superconductors

2015

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“…Early work focused on the most easily measurable quantity, the DC conductivity. [1-3, 6-10] Recently, due to the availability of local scanning probes, attention has turned to the tunneling behavior [11][12][13][14][15]. In the case of the disorder-tuned SIT [15], it has become clear that the SIT is ultimately due to a bosonic mechanism [16] rather than a fermionic one [17].…”

mentioning

confidence: 99%

Divergence of dynamical conductivity at certain percolative superconductor-insulator transitions

Loh¹,

Dhakal²,

Neis³

et al. 2014

J. Phys.: Condens. Matter

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Random inductor-capacitor (LC) networks can exhibit percolative superconductor-insulator transitions (SITs). We use a simple and efficient algorithm to compute the dynamical conductivity σ(ω, p) of one type of LC network on large (4000 × 4000) square lattices, where δ = p − pc is the tuning parameter for the SIT. We confirm that the conductivity obeys a scaling form, so that the characteristic frequency scales as Ω ∝ |δ| νz with νz ≈ 1.91, the superfluid stiffness scales as Υ ∝ |δ| t with t ≈ 1.3, and the electric susceptibility scales as χE ∝ |δ| −s with s = 2νz − t ≈ 2.52. In the insulating state, the low-frequency dissipative conductivity is exponentially small, whereas in the superconductor, it is linear in frequency. The sign of Im σ(ω) at small ω changes across the SIT. Most importantly, we find that right at the SIT Re σ(ω) ∝ ω t/νz−1 ∝ ω −0.32 , so that the conductivity diverges in the DC limit, in contrast with most other classical and quantum models of SITs. [4,5]. As a quantum phase transition occurring at zero temperature, this superconductor-insulator transition (SIT) has attracted much interest. Early work focused on the most easily measurable quantity, the DC conductivity.[1-3, 6-10] Recently, due to the availability of local scanning probes, attention has turned to the tunneling behavior [11][12][13][14][15]. In the case of the disorder-tuned SIT [15], it has become clear that the SIT is ultimately due to a bosonic mechanism [16] rather than a fermionic one [17]. The last step towards a full characterization of the SIT is to develop an understanding of the behavior of the AC conductivity. This is a powerful probe of fluctuations on both long and short length and time scales, and it is of great interest especially as recent technological developments begin to open up more windows of the electromagnetic spectrum for measurement [18][19][20][21].One of the most important questions concerns the AC conductivity in the "collisionless DC" limit [22,23] [52], σ * = lim ω→0 lim T →0 σ(ω, T ). This has been the subject of a large body of work, including analytical arguments involving charge-vortex duality arguments, quantum Monte Carlo calculations in various representations, and experiments [1,4,16,23,[25][26][27][28][29][30][31][32]. It is often claimed that at the SIT σ * is finite and takes a universal value of the order of σ Q = 4e 2 /h, but there are large discrepancies between the "universal" values from various studies, and it is not clear whether there really is a universal value.

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“…1, indicating a similar energy gap but, importantly, almost no coherence peaks at the gap edges are present. This reminds the evolution of spectra found in strongly disordered InO [2] and NbN [3]. Moreover, a reduced tunnelling conductance around the zero bias is found here also for temperatures above the resistive T c = 3.8 K. The dotted and dashed curves in Fig.…”

Section: Resultsmentioning

confidence: 52%

“…A question has been raised if at the transition the Cooper pairs become localized, or rst the superconductivity is suppressed and then the standard localisation of single electrons leads to insulating state. Recent tunnelling experiments on homogenously disordered superconducting lms [2,3] accumulated a support for the rst hypothesis. It has been shown that in highly disordered lms the coherence peaks in the superconducting density of states disappear close to SIT but superconducting gap can be found even above the resistive transition temperatures T c , reminding the pseudo-gap in high-T c cuprates.…”

Section: Introductionmentioning

confidence: 93%

Superconductivity Near Transition to Insulating State in MoC Ultrathin Films Studied by Subkelvin STM

et al. 2014

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We study the homogeneously disordered MoC thin lms with thicknesses of 10 and 5 nm and the superconducting transition temperatures near 6 and 4 K, signicantly decreased as compared to the bulk Tc = 8.32 K due to a disorder. The scanning tunnelling spectroscopy reveals in the thicker sample a BCS superconducting energy gap ∆ with a broadening parameter Γ equal to about 10 per cent of ∆. Remarkably, Γ increases with temperature. The thinner, more disordered sample shows a gapped superconducting density of states but without any coherence peaks at the gap edge, which could not be approximated by the BCS DOS. Moreover, the reduced DOS around the Fermi level persists above the resistive transition temperature reminding the pseudo-gap known from high-Tc cuprates.

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Phase Fluctuations in a Strongly Disordereds-Wave NbN Superconductor Close to the Metal-Insulator Transition

Cited by 184 publications

References 36 publications

Amplitude, density, and current correlations of strongly disordered superconductors

Amplitude, density, and current correlations of strongly disordered superconductors

Divergence of dynamical conductivity at certain percolative superconductor-insulator transitions

Superconductivity Near Transition to Insulating State in MoC Ultrathin Films Studied by Subkelvin STM

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