Island formation in disordered superconducting thin films at finite magnetic fields

Dubi, Yonatan; Meir, Yigal; Avishai, Y.

doi:10.1103/physrevb.78.024502

Cited by 23 publications

(27 citation statements)

References 42 publications

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“…This is supported by numerical [12,17] and experimental [11,[20][21][22][23] data. (2) Some of these SCIs are coherently coupled, forming a larger SC cluster.…”

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confidence: 63%

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Magnetoresistance anisotropy in amorphous superconducting thin films: Site-bond percolation approach

Porat

Meir

2015

Phys. Rev. B

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Recent measurements of the magnetoresistance (MR) of amorphous superconducting thin films in tilted magnetic fields have displayed several surprising experimental details, in particular a strong dependence of the MR on field angle at low magnetic fields, which diminishes and then changes sign at large fields. Using a generalized site-bond percolation model, that takes into account both the orbital and Zeeman effects of the magnetic field, we show that the resulting MR curves reproduce the main experimental features. Such measurements, accompanied by the corresponding theory, may be crucial in pinpointing the correct theory of the superconductor-insulator transition and of the MR peak in thin disordered films. [7]. Over the years, several paradigms for the transition have been put forward, which can be broadly grouped into a pure bosonic paradigm, so called the "dirty boson" model [8][9][10], and variants of the percolation model [11][12][13][14][15][16][17]. A further insight into the nature of the transition was made possible due to magneto-resistance (MR) measurements in the normal phase [18,19], where giant resistance peak has been observed beyond the SIT, followed by a dramatic drop as the field is further increased. This dramatic observation has been explained by a phenomenological percolation approach [15], which emphasized the competition between the SC and the fermionic degrees of freedom, due to the persistence of SC islands (SCIs) into the insulating phase. An alternative explanation, based on the boson-only picture was put forward in Ref. [10], where the role of the fermionic degrees of freedom was played by vortices.While experiments indeed indicated the formation of SC puddles [11,[20][21][22][23] and of critical (classical or quantum) percolation behavior [2,[24][25][26][27][28], it is clear that more experimental data are needed to establish the nature of the transition and of the insulating phase. In recent years, detailed examinations of the MR dependence on the direction of the field were performed [29,30] (see Fig. 1(a) and (b)). The main observations are (1) highly anisotropic MR in the low field regime, reflected by high dependence of MR amplitude, SIT critical field B c and MR peak field B max on the field direction. (2) Lower peak resistance was measured for shallower angles. (3) The magnitude of the anisotropy decreases with the strength of the field, up to a point beyond the peak, where the MR curves seem to converge to isotropic MR, that is, angle independent resistance at a certain magnetic field intensity B iso . (4) In samples that are SC at zero field the anisotropy is reversed at higher fields, i.e., higher resistance for shallower angles [29], while samples that are insulating at zero field depict nearly isotropic behavior for all B > B iso [30].These new results are yet to be accounted for in any of the theoretical pictures for the SIT, and thus are a key observation to discern the correct theory. In this letter we demonstrate that a phenomenological model within the framework o...

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“…This is supported by numerical [12,17] and experimental [11,[20][21][22][23] data. (2) Some of these SCIs are coherently coupled, forming a larger SC cluster.…”

supporting

confidence: 63%

“…17 as a shift of the gap distribution towards zero. This is manifested in the model by a uniform shift of all the local gaps by the orbital field, ∆ i → ∆ i −χB n ⊥ , where the susceptibility χ and the exponent n are the parameters defining the dependence of the gap distribution on the orbital field.…”

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confidence: 95%

Magnetoresistance anisotropy in amorphous superconducting thin films: Site-bond percolation approach

Porat

Meir

2015

Phys. Rev. B

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“…In particular, the gap and order parameter are driven to zero with increasing disorder, whereas they remain nonzero, and can even increase, when both species see the same energy landscape. This destruction of pairing has also been seen in BdG studies in the presence of spin-independent order and a uniform Zeeman field [9]. Furthermore, the gapless superconducting state is highly inhomogeneous and survives to much larger disorder by virtue of the order parameter becoming inhomogeneous in the presence of spin-dependent disorder, which strongly modifies AG's classical work.…”

Section: Introductionmentioning

confidence: 59%

“…These states can exist in two dimensions in a disordered system below a critical disorder even when all the singleparticle states are localized. The ensuing superconductor-insulator transition has been studied in considerable detail in the literature [7][8][9]. A particularly intriguing aspect of cold atoms is the ability to tune the interactions either through the Feshbach resonance or through optical lattices.…”

Section: Introductionmentioning

confidence: 99%

Gapless inhomogeneous superfluid phase with spin-dependent disorder

et al. 2013

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We show that the presence of a spin-dependent random potential in a superconductor or a superfluid atomic gas leads to distinct transitions at which the energy gap and average order parameter vanish, generating an intermediate gapless superfluid phase, in marked contrast to the case of spin-symmetric randomness where no such gapless superfluid phase is seen. By allowing the pairing amplitude to become inhomogeneous, the gapless superconducting phase persists up to considerably higher disorder compared with the prediction of Abrikosov-Gorkov. The low-lying excited states are located predominantly in regions where the pairing amplitude vanishes and coexist with the superfluid regions with a finite pairing. Our results are based on inhomogeneous Bogoliubov-de Gennes mean field theory for a two-dimensional attractive Hubbard model with spin-dependent disorder.

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“…Indeed, as we show in this Communication, disorder renders collective modes -optically inactive in a clean superconductorvisible. By analyzing a prototype fermionic model, the attractive Hubbard model with on-site disorder [11][12][13][14][15][16] , we reveal that thanks to the breaking of translational invariance the collective modes couple to light via an intermediate particle-hole excitation process. Most remarkably, this coupling leads to the emergence of additional optical absorption, mainly due to phase modes, below the BCSlike threshold for a photon to break apart a Cooper pair, in agreement with recent experimental observations 17,18 .…”

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confidence: 99%

Optical excitation of phase modes in strongly disordered superconductors

et al. 2014

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According to the Goldstone theorem the breaking of a continuous U(1) symmetry comes along with the existence of low-energy collective modes. In the context of superconductivity these excitations are related to the phase of the superconducting (SC) order parameter and for clean systems are optically inactive. Here we show that for strongly disordered superconductors phase modes acquire a dipole moment and appear as a subgap spectral feature in the optical conductivity. This finding is obtained with both a gauge-invariant random-phase approximation scheme based on a fermionic Bogoliubov-de Gennes state as well as with a prototypical bosonic model for disordered superconductors. In the strongly disordered regime, where the system displays an effective granularity of the SC properties, the optically active dipoles are linked to the isolated SC islands, offering a new perspective for realizing microwave optical devices.

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Island formation in disordered superconducting thin films at finite magnetic fields

Cited by 23 publications

References 42 publications

Magnetoresistance anisotropy in amorphous superconducting thin films: Site-bond percolation approach

Magnetoresistance anisotropy in amorphous superconducting thin films: Site-bond percolation approach

Gapless inhomogeneous superfluid phase with spin-dependent disorder

Optical excitation of phase modes in strongly disordered superconductors

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