Insulator-to-superconductor transition in ultrathin films

Liu, Y.; Haviland, D. B.; Nease, B.; Goldman, A. M.

doi:10.1103/physrevb.47.5931

Cited by 107 publications

(102 citation statements)

References 56 publications

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“…We can only note that the reentrant behavior of the conductivity seems to be a consequence of the granularity. Homogeneous films made from the same material having no (or less pronounced) granular structure do not show such a behavior (Liu et al, 1993).…”

Section: Transport Properties Of Granular Superconductorsmentioning

confidence: 99%

“…One can see that there exists a critical value of the normal state resistance R 0 close to the value of quantum resistance h/(2e) 2 ≈ 6.4k Ω such that samples with resistance R < R 0 eventually become superconducting under temperature decrease, while those with R > R 0 show tendency to the insulating behavior. Such a behavior turned out to be generic and was observed in a number of granular (as well as on homogeneously disordered, (Frydman et al, 2002;Liu et al, 1993;Marković et al, 1999)) films made from different materials.…”

Section: Fig 12mentioning

confidence: 99%

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Granular electronic systems

et al. 2007

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A granular metal is an array of metallic nano-particles imbedded into an insulating matrix. Tuning the intergranular coupling strength a granular system can be transformed into either a good metal or an insulator and, in case of superconducting particles, experience superconductor-insulator transition. The ease of adjusting electronic properties of granular metals makes them most suitable for fundamental studies of disordered solids and assures them a fundamental role for nanotechnological applications. This Review discusses recent important theoretical advances in the study of granular metals, emphasizing on the interplay of disorder, quantum effects, fluctuations and effects of confinement in formation of electronic transport and thermodynamic properties of granular materials.

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Section: Transport Properties Of Granular Superconductorsmentioning

confidence: 99%

Section: Fig 12mentioning

confidence: 99%

Granular electronic systems

et al. 2007

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“…In principle, electrons can be spatially localized, either as a consequence of the random potential, which leads to Anderson localization (46), or of interactions, which results in a Mott insulator, or a combination of both (47). In the case of single-layer FeSe/SrTiO 3 films, during the annealing process, in addition to the electron concentration increase in the S phase (21), there are two other concomitant processes with the change of the relative amount of the N phase and S phase, and the change in the overall sample composition.…”

Section: Discussionmentioning

confidence: 99%

Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO ₃ films

Zhang

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator-superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator-superconductor crossover observed in the single-layer FeSe film grown on a SrTiO 3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator-superconductor crossover in FeSe/SrTiO 3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator-superconductor crossover may be associated with the twodimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature.single-layer FeSe/SrTiO 3 films | insulator-to-superconductor crossover | ARPES T he iron-based superconductors (1-4) represent the second class of high-temperature superconductors after the discovery of the first class of high-temperature cuprate superconductors. It is now generally agreed that the superconductivity in cuprates is realized by doping a Mott (charge transfer) insulator (5). In the iron-based superconductors, however, the parent compounds mostly exhibit a poor metallic behavior with an antiferromagnetic order, thus raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture (6-18), particularly whether the picture of doping a Mott insulator is relevant to the iron-based superconductors (1,3,11,16,17). Some theoretical calculations indicate that the iron-based superconductors may be in proximity to a Mott insulator (11,16,17), and attempts have also been made to unify cuprates and ironbased superconductors in theory (18). However, so far no clear experimental evidence of doping (or carrier concentration)-induced insulator-superconductor transition (or crossover) has been reported in the iron-based superconductors.The latest discovery of possible high-temperature superconductivity in the single-layer FeSe films grown on a SrTiO 3 substrate has attracted much attention both experimentally (19)(20)(21)(22)(23)(24)(25)(26)(27) and theoretically (28-32). The reduced dimensionality with enhanced interfacial effect makes ...

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“…Moreover, data were also discarded when it was stated clearly by the authors that the films were too thin to be continuous or to allow reliable measurements (some of the published data were sent by the authors of these publications). A complete list of the collected and presented data, and the cross-checking and discussion of each data set are given in the Supplemental Material [38] (which also includes the works presented in references [57][58][59][60][61][62][63][64][65][66][67]). …”

Section: Appendix: Materials and Methodsmentioning

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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Insulator-to-superconductor transition in ultrathin films

Cited by 107 publications

References 56 publications

Granular electronic systems

Granular electronic systems

Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO ₃ films

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

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Insulator-to-superconductor transition in ultrathin films

Cited by 107 publications

References 56 publications

Granular electronic systems

Granular electronic systems

Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO 3 films

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

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Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO ₃ films