Orateur
Description
Beyond a critical disorder, two-dimensional superconductors become insulating at the Superconductor-Insulator Transition (SIT) [1-2]. We present an experimental study on insulating a-YxSi1-x films in the vicinity of the SIT, as well as corresponding numerical simulations of the electrical conductivity [3]. At the lowest temperatures, electronic transport is activated.
On the insulating side, our results indicate a bistability in the current-voltage characteristics, with jumps in the current of several orders of magnitude [4,5] and which we analyze in terms of electron-phonon decoupling [6]. We extend the hot-electron model [7] to explain different features of the experimental results. We perform numerical simulations in which grains are at an effective temperature and electron jumps between them are due to the hopping term. These simulations can reproduce the most significant features of the experimental results.
We also present experimental results on disordered InSb thin films where apparently similar jumps to those observed in the previous systems take place. However, the hot-electron model is not able to explain these jumps. They seem to be driven by transitions from a rigid phase to a fluid one [8,9]. We analyze and compare the difference between both types of systems.
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[2] Sacépé, B. et al. Localization of preformed Cooper pairs in disordered superconductors. Nat. Phys. 7, 239–244 (2011).
[3] Humbert, V., Ortuno, M., Somoza, A.M., Bergé, L., Dumoulin, L. & Marrache-Kikuchi, C.A. Overactivated transport in the localized phase of the superconductor-insulator transition. Nature Comm., 12, 6733 (2021).
[4] Ovadia, M. and Sacepe, B. and Shahar, D. Electron-Phonon Decoupling in Disordered Insulators, Phys. Rev. Lett. 102, 176802 (2009).
[5] Ladieu, F. and L'Hote, D. and Tourbot, R. Non-Ohmic hopping transport in a-YSi: From isotropic to directed percolation. Phys. Rev. B 61, 8108 (2000).
[6] Altshuler, B. L. and Kravtsov, V. E. and Lerner, I. V. and Aleiner, I. L. Jumps in Current-Voltage Characteristics in Disordered Films, Phys. Rev. Lett. 102, 176803 (2009).
[7] Wang, Ning and Wellstood, F. C. and Sadoulet, B. and Haller, E. E. and Beeman, J. Electrical and thermal properties of neutron-transmutation-doped Ge at 20 mK, Phys. Rev. B 41, 3761 (1990).
[8] Porrati, F. and Huth, M. Resistive switching in tunable Pt–C granular metals, J. Appl. Phys. 139, 185103 (2026).
[9] Shashkina, A.A., Melnikova, M.Yu, and Kravchenko, S.V. Transport evidence for the quantum Wigner solid formation in two-dimensional electron systems, Physica E 168, 116192 (2025).