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Séminaire matériaux 2D de l’INSP

The superconductor-insulator transition out of equilibrium - Idan Tamir - Wednesday October 9th-4pm

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Idan Tamir - PhD student at Weizman Institute (Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel. Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany)

Abstract

For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it (for review see [1]). We show that this metallic state can be eliminated by adequately filtering external radiation, and that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations [2].

Not surprisingly, the bordering insulating phase (driven via applying an external magnetic field, increasing disorder or film thickness, etc. [3]) is also sensitive to similar perturbation. While applying a small voltage bias is sufficient to drive the system out of equilibrium, indicated by nonlinear and even discontinuous current-voltage characteristics [4], the high resistances observed at this phase (in series with the measurement wires capacitance) effectively filters external noises allowing us to more easily probe the insulating ground state. Indeed, recent experimental reports were able to demonstrate a rapid decay of conductivity, which suggests the existence of a finite-temperature insulator bordering the superconductor-insulator transition [5-6]. This decay over a narrow temperature range was theoretically linked to both a finite-temperature transition to a many-body-localized state, and to a charge-Berezinskii-Kosterlitz-Thouless transition. We present low-frequency noise measurements results of such insulators, performed as a test for many-body localization, exhibiting a huge enhancement of noise when exceeding the threshold voltage for nonlinear conductivity [7].

Finally, we show that close to the transition, the insulating phase becomes unstable with respect to any applied voltage making it, at least experimentally, immeasurable. We believe that this instability is general and should occur in various systems while approaching their quantum critical point [8].

[1] Kapitulnik, Aharon, Steven A. Kivelson, and Boris Spivak. « Colloquium : anomalous metals : failed superconductors. » Reviews of Modern Physics 91, no. 1 (2019) : 011002.

[2] Tamir, I., A. Benyamini, E. J. Telford, F. Gorniaczyk, A. Doron, T. Levinson, D. Wang et al. « Sensitivity of the superconducting state in thin films. » Science advances 5, no. 3 (2019) : eaau3826.

[3] Gantmakher, Vsevolod F., and Valery T. Dolgopolov. « Superconductor–insulator quantum phase transition. » Physics-Uspekhi 53, no. 1 (2010) : 1.

[4] Ovadia, M., B. Sacépé, and D. Shahar. « Electron-phonon decoupling in disordered insulators. » Physical review letters 102, no. 17 (2009) : 176802.

[5] Ovadia, M., D. Kalok, I. Tamir, S. Mitra, B. Sacépé, and D. Shahar. « Evidence for a finite-temperature insulator. » Scientific reports 5 (2015) : 13503.

[6] Mironov, Alexey Yu, Daniel M. Silevitch, Thomas Proslier, Svetlana V. Postolova, Maria V. Burdastyh, Anton K. Gutakovskii, Thomas F. Rosenbaum, Valerii V. Vinokur, and Tatyana I. Baturina. « Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films. » Scientific reports 8, no. 1 (2018) : 4082.

[7] Tamir, I., T. Levinson, F. Gorniaczyk, A. Doron, J. Lieb, and D. Shahar. « Excessive noise as a test for many-body localization. » Physical Review B 99, no. 3 (2019) : 035135.

[8] Doron Adam, Idan Tamir, Tal Levinson, Maoz Ovadia, Benjamin Sacépé, and Dan Shahar. « Instability of insulators near quantum phase transitions. » Physical review letters 119, no. 24 (2017) : 247001.