We are currently working on two issues : the electron glass and the AlOx/SrTiO3 interface.
During the past twenty years, a few experimental groups in the world have observed that in some disordered insulators, at low temperature, the application of a gate voltage or of other perturbations induce very slow (days long) relaxations of the electrical conductance. These were suggested to be the first experimental evidences of the “electron glass”. Glasses are systems with such a slow internal dynamics that they cannot reach their thermodynamic equilibrium within any experimentally accessible time. Famous examples in condensed matter are structural and spin glasses. It was theoretically suggested in the 80ies, that the electrons can “freeze” at low temperature in disordered insulators (Anderson insulators) due to the coexistence of disorder and ill-screened electron-electron interactions, giving rise to the so-called “electron glass”. We aim to characterize these slow relaxations and to understand their nature (is it the “electron glass” or something else ?).
 J. Delahaye, T. Grenet, C. Marrache-Kikuchi, L. Bergé, A.A. Drillien, “Observation of thermally activated glassiness and memory dip in a Nb-Si insulating thin films”, Eur. Phys. Lett. 106, p. 67006 (2014) [arXiv,EPL]
SrTiO3 crystals are insulators with a band gap of 3.2eV but their surface can be transformed into a metallic (and even a superconducting) state by different techniques such as ion milling, ultra-violet exposure or pulsed laser deposition of an oxide layer. We have recently shown that a metallic state can also be induced by the electron beam evaporation of a granular Al or an amorphous alumina layer (AlOx) at room temperature. We are investigating the electronic properties of this SrTiO3/AlOx interface, which display spectacular electric field and photoconductive effects.
Granular Al, amorphous NbxSi1-x and discontinuous Au thin films, AlOx/SrTiO3 interface.
electron-gun evaporation, electrical resistance (high resistance, low current noise) versus temperature, electrical field-effect.
Aviad Frydman (Bar-Ilan University, Israel), Zvi Ovadyahu (Hebrew University of Jerusalem), Miguel Ortuno and Andrés Somoza (Universitad de Murcia, Spain), Claire Marrache-Kikuchi (CSNSM, Orsay).