Cooper-pair insulator phase in superconducting amorphous Bi films induced by nanometer-scale thickness variations

Hollen, Shawna M.; Nguyễn, Hồng Quang; Rudisaile, E.; Stewart, M. D.; Shainline, Jeffrey M.; Xu, Jimmy; Valles, James M.

doi:10.1103/physrevb.84.064528

Cited by 34 publications

(48 citation statements)

References 37 publications

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“…Using this embedded hole array technique, we previously uncovered a CPI phase in a-Bi films deposited on anodized aluminum oxide (AAO) substrates [15]. Later we found that these substrates induced spatial film thickness variations and thus, Cooper pairing inhomogeneities that could give rise to a bosonic SIT [29]. Here, we present results from similar experiments on a-Bi films fabricated to be uniformly thick by using atomically flat Si substrates.…”

Section: Introductionmentioning

confidence: 74%

Collapse of the Cooper pair phase coherence length at a superconductor-to-insulator transition

Hollen

Fernandes

et al. 2013

Phys. Rev. B

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We present investigations of the superconductor to insulator transition (SIT) of uniform a-Bi films using a technique sensitive to Cooper pair phase coherence. The films are perforated with a nanohoneycomb array of holes to form a multiply connected geometry and subjected to a perpendicular magnetic field. Film magnetoresistances on the superconducting side of the SIT oscillate with a period dictated by the superconducting flux quantum and the areal hole density. The oscillations disappear close to the SIT critical point to leave a monotonically rising magnetoresistance that persists in the insulating phase. These observations indicate that the Cooper pair phase coherence length, which is infinite in the superconducting phase, collapses to a value less than the interhole spacing at this SIT. This behavior is inconsistent with the gradual reduction of the phase coherence length expected for a bosonic, phase fluctuation driven SIT. This result starkly contrasts with previous observations of oscillations persisting in the insulating phase of other films implying that there must be at least two distinct classes of disorder tuned SITs. 1 arXiv:1301.6155v2 [cond-mat.supr-con] 4 Feb 2013Superconductor to insulator quantum phase transitions (SIT) can be induced in a wide range of quasi two-dimensional superconducting systems, including elemental films, high T c superconductors, organic superconductors and superconductor graphene composites [1][2][3][4][5][6][7][8]. Remarkably, these transitions occur, nearly universally, at a critical normal state resistance, R Nc ≃ R Q = h (2e) 2 , and film resistances often show scaling behavior around this critical point. The most prominent theories that can account for these behaviors view the SIT as a Cooper pair or boson localization transition, rather than a Cooper pair breaking transition [9][10][11][12][13][14]. Recent experiments that probe films near the SIT in new ways have provided more details that support this "bosonic" picture of the SIT [15][16][17][18][19]. For example, scanning tunneling microscopy (STM) has revealed that spatial inhomogeneities develop in the order parameter on approaching the SIT suggesting that Cooper pairs localize into islands [19,20]. High frequency transport measurements indicate that a finite superfluid density persists in non-superconducting films [21]. Here, we describe experiments employing a technique that is uniquely sensitive to the length scale that diverges at a bosonic SIT: the phase coherence length ξ φ . This technique previously revealed that Cooper pairs maintain their phase coherence over 100's of nanometers through the SITs of two distinct film systems [15,22].For this work, we investigate a third film system [23][24][25] that is likely to provide the most stringent test of whether the bosonic SIT is generic to thin films. This phase sensitive technique requires patterning films with an array of nanometer-scale holes.The hole patterning creates a simply connected geometry that leads to Little-Parks-like (LP) oscillations...

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Section: Introductionmentioning

confidence: 74%

Collapse of the Cooper pair phase coherence length at a superconductor-to-insulator transition

Hollen

Fernandes

et al. 2013

Phys. Rev. B

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“…This suggests that effects of quenched disorder introduced by the fabrication process may be significant. Disorder in the weak links between superconducting "grains" can arise from inhomogeneities in the film thickness induced by the substrate 19 . In fact, it has been shown numerically 17 that for the model of Eq.…”

Section: Numerical Results and Discussionmentioning

confidence: 99%

“…In part, this is due to the lack of experimental data for artificial arrays in this geometry. Recently, however, there has been a growing interest in a related system, in the form of an ultra-thin superconducting film with a triangular lattice of nanoholes [18][19][20][21][22] . A simple model for this system consists of a Josephson-junction array on a honeycomb lattice, with the triangular lattice of nanoholes corresponding to the dual lattice, and it has already been used to investigated the thermal resistive transition in absence of charging effects 17 .…”

Section: Introductionmentioning

confidence: 99%

Superconductor-insulator transition of Josephson-junction arrays on a honeycomb lattice in a magnetic field

Granato

2016

Eur. Phys. J. B

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We study the superconductor to insulator transition at zero temperature in a Josephson-junction array model on a honeycomb lattice with f flux quantum per plaquette. The path integral representation of the model corresponds to a (2+1)-dimensional classical model, which is used to investigate the critical behavior by extensive Monte Carlo simulations on large system sizes. In contrast to the model on a square lattice, the transition is found to be first order for f = 1/3 and continuous for f = 1/2 but in a different universality class. The correlation-length critical exponent is estimated from finite-size scaling of vortex correlations. The estimated universal conductivity at the transition is approximately four times its value for f = 0. The results are compared with experimental observations on ultrathin superconducting films with a triangular lattice of nanoholes in a transverse magnetic field.

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“…These variations are inferred from analysis of AFM topographs of the anodized aluminum oxide (AAO) substrates used as templates for the NHC films. The topographs revealed regular, nanoscale height variations [19]. Since the local deposition thickness depends on the local slope of the substrate, these height variations lead to film thickness variations.…”

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confidence: 99%

“…The resulting films acquire the NHC geometry of the underlying AAO substrate, and also develop thickness variations due to the changing local slope of the AAO (see ref. [19]). The holes form a roughly triangular array with an average hole radius of 17±9nm and spacing of 85±30nm (see Fig.…”

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Cooper pair insulator phase induced in amorphous Pb0.9Bi0.1 thin films

Hollen

Shainline

et al. 2013

Physica C: Superconductivity

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A Cooper pair insulator (CPI) phase emerges near the superconductor-insulator transitions of a number of strongly-disordered thin film systems. Much recent study has focused on a mechanism driving the underlying Cooper pair localization. We present data showing that a CPI phase develops in amorphous Pb 0.9 Bi 0.1 films deposited onto nano-porous anodized aluminum oxide surfaces just as it has been shown to develop for a-Bi films. This result confirms the assertion that the CPI phase emerges due to the structure of the substrate. It supports the picture that nanoscale film thickness variations induced by the substrate drive the localization. Moreover, it implies that the CPI phase can be induced in any superconducting material that can be deposited onto this surface.

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Cooper-pair insulator phase in superconducting amorphous Bi films induced by nanometer-scale thickness variations

Cited by 34 publications

References 37 publications

Collapse of the Cooper pair phase coherence length at a superconductor-to-insulator transition

Collapse of the Cooper pair phase coherence length at a superconductor-to-insulator transition

Superconductor-insulator transition of Josephson-junction arrays on a honeycomb lattice in a magnetic field

Cooper pair insulator phase induced in amorphous Pb0.9Bi0.1 thin films

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