Correlated Conductance Fluctuations Close to the Berezinskii-Kosterlitz-Thouless Transition in Ultrathin NbN Films

Koushik, R.; Kumar, Shiva; Amin, Kazi Rafsanjani; Mondal, Mintu; Jesudasan, John; Bid, Aveek; Raychaudhuri, Pratap; Ghosh, Arindam

doi:10.1103/physrevlett.111.197001

Cited by 38 publications

(46 citation statements)

References 39 publications

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“…Meanwhile, theoretical studies have revealed the ergodicity breaking [12] and the onset of out-of-equilibrium dynamics near T BKT [13]. However, except for a recent study of thin films of NbN [14], there have been no attempts, to the best of our knowledge, to probe the correlations in the BKT critical regime and the low-T phase. Furthermore, studies of the BKT physics in thin films of conventional superconductors, such as NbN, are complicated by the still not-well-understood relationship between film thickness, disorder, and superconductivity [15].…”

Section: Introductionmentioning

confidence: 99%

Evidence for correlated dynamics near the Berezinskii-Kosterlitz-Thouless-like transition in highly underdopedLa2−xSrxCuO4

Shi¹,

Shi²,

Popović³

2016

Phys. Rev. B

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Section: Introductionmentioning

confidence: 99%

Evidence for correlated dynamics near the Berezinskii-Kosterlitz-Thouless-like transition in highly underdopedLa2−xSrxCuO4

Shi¹,

Shi²,

Popović³

2016

Phys. Rev. B

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“…We chose sputtered NbN as the material for this study for four main reasons: (a) It is widely researched, and experimental data collected for different growth methods and conditions are available; (b) there are contradicting reports about which of the existing models describes the T c suppression in NbN films-for instance, Kang et al [18] proposed that T c is suppressed due to the quantum size effect, Wang et al [17] suggested that the suppression follows Finkel'stein's model [9], Semenov et al [19] determined that the suppression is governed by the proximity effect, and Koushik et al [39] argued that the transition is of a BKT type; (c) the relatively high T c of NbN (16 K for a bulk NbN [40]) assists the experimental investigation; and (d) its properties make it useful for photodetectors [34,36,41,42].…”

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confidence: 99%

Universal scaling of the critical temperature for thin films near the superconducting-to-insulating transition

et al. 2014

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Thin superconducting films form a unique platform for geometrically confined, strongly interacting electrons. They allow an inherent competition between disorder and superconductivity, which in turn enables the intriguing superconducting-to-insulating transition and is believed to facilitate the comprehension of high-T c superconductivity. Furthermore, understanding thin film superconductivity is technologically essential, e.g., for photodetectors and quantum computers. Consequently, the absence of established universal relationships between critical temperature (T c ), film thickness (d), and sheet resistance (R s ) hinders both our understanding of the onset of the superconductivity and the development of miniaturized superconducting devices. We report that in thin films, superconductivity scales as dT c (R s ). We demonstrated this scaling by analyzing the data published over the past 46 years for different materials (and facilitated this database for further analysis). Moreover, we experimentally confirmed the discovered scaling for NbN films, quantified it with a power law, explored its possible origin, and demonstrated its usefulness for nanometer-length-scale superconducting film-based devices. Relationships between low-temperature and normal-state properties are crucial for understanding superconductivity. For instance, the Bardeen-Cooper-Schrieffer theory (BCS) successfully associates the normal-to-superconducting transition temperature, T c , with material parameters, such as the Debye temperature ( D ) and the density of states at the Fermi level [N (0)]. Hence, the BCS model allows us to infer superconducting characteristics (i.e., T c ) from properties measured at higher temperatures [1]. In the BCS framework, superconductivity occurs when attractive phonon-mediated electron-electron interactions overcome the Coulomb repulsion, giving rise to paired electrons (Cooper pairs) with a binding energy gap:. Moreover, within a superconductor, all Cooper pairs are coupled, giving rise to a collective electron interaction. Such a collective state is described by a complex global order parameter with real amplitude ( ) and phase (ϕ): = e iϕ .Because superconductivity relies on a collective electron behavior, the onset of superconductivity occurs when the number of participating electrons is just enough to be considered collective, i.e., at the nanoscale [2-5]. Thus, it is known that the superconductivity-disorder interplay varies in thin films and is effectively tuned with the film thickness (d) or with the disorder in the system, which is represented by sheet resistance of the film at the normal state (R s ) [6][7][8][9][10]. The mechanism of superconductivity in thin films has been investigated since the 1930s [6] increase in T c with decreasing thickness in aluminum films in a study that pioneered the currently ongoing research of thin superconducting films. This enhancement of T c , which is still not completely understood, was later confirmed by Strongin et al. [12], who also reported the more common be...

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“…This, in turn, would introduce significant non-Gaussian components (NGCs) in the resistance fluctuations which can be experimentally probed by studying the higher-order statistics of the measured noise. To test whether the noise in this temperature range originates from glassy dynamics we calculated the fourth moment of voltage fluctuations, what is commonly known in as the "second spectrum" [39][40][41]. Physically, the second spectrum represents the fluctuations in the PSD with time in the chosen frequency octave.…”

Section: N Vmentioning

confidence: 99%

“…The details of the calculation method are given in Ref. [39]. The normalized value of the second spectrum σ (2) is given by…”

Section: N Vmentioning

confidence: 99%

Probing the interplay between surface and bulk states in the topological Kondo insulatorSmB6through conductance fluctuation spectroscopy

2017

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We present results of resistance fluctuation spectroscopy on single crystals of the predicted Kondo topological insulator material SmB 6 . Our measurements show that at low temperatures, transport in this system takes place only through surface states. The measured noise in this temperature range arises due to universal conductance fluctuations whose statistics was found to be consistent with theoretical predictions for that of two-dimensional systems in the symplectic symmetry class. At higher temperatures, we find signatures of glassy dynamics and establish that the measured noise is caused by mobility fluctuations in the bulk. We find that, unlike the topological insulators of the dichalcogenide family, the noises in surface and bulk conduction channels in SmB 6 are completely uncorrelated. Our measurements establish that at sufficiently low temperatures, the bulk has no discernible contribution to electrical transport in SmB 6 , making it an ideal platform for probing the physics of topological surface states.

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Correlated Conductance Fluctuations Close to the Berezinskii-Kosterlitz-Thouless Transition in Ultrathin NbN Films

Cited by 38 publications

References 39 publications

Evidence for correlated dynamics near the Berezinskii-Kosterlitz-Thouless-like transition in highly underdopedLa2−xSrxCuO4

Evidence for correlated dynamics near the Berezinskii-Kosterlitz-Thouless-like transition in highly underdopedLa2−xSrxCuO4

Universal scaling of the critical temperature for thin films near the superconducting-to-insulating transition

Probing the interplay between surface and bulk states in the topological Kondo insulatorSmB6through conductance fluctuation spectroscopy

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