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We have observed reproducible conductance fluctuations at low temperature in a small GaAs:Si wire driven across the Anderson transition by the application of a gate voltage. We analyse quantitatively the log-normal conductance statistics in terms of truncated quantum fluctuations. Quantum fluctuations due to small changes of the electron energy (controlled by the gate voltage) cannot develop fully due to identified geometrical fluctuations of the resistor network describing the hopping through the sample. The evolution of the fluctuations versuselectron energy and magnetic field shows that the fluctuations are non-ergodic, except in the critical insulating region of the Anderson transition, where the localization length is larger than the distance between Si impurities. The mean magnetoconductance is in good accordance with simulations based on the Forward-Directed-Path analysis, i.e. it saturates to ln(σ(H>1)/σ(0)) ≈1, as σ(0) decreases over orders of magnitude in the strongly localized regime.

Abstract: In this paper, we review several important features of the out-of-equilibrium dynamics of spin glasses. Starting with the simplest experiments, we discuss the scaling laws used to describe the isothermal aging observed in spin glasses after a quench down to the low-temperature phase. We report in particular new results on the sub-aging behaviour of spin glasses. We then discuss the rejuvenation and memory effects observed when a spin glass is submitted to temperature variations during aging, from the point of view of both energy landscape pictures and real-space pictures. We highlight the fact that both approaches point out the necessity of hierarchical processes involved in aging. Finally, we report an investigation of the effect of small temperature variations on aging in spin glass samples with various anisotropies which indicates that this hierarchy depends on the spin anisotropy.

Heatings produced by the irradiation with light ion microbeams were measured in situby using microthermocouples deposited and etched onto a SiO2glass substrate. For a given distance rbetween the microbeam centre and the thermocouple, we show that the heating averaged over the irradiation time decreases as 1/r, in agreement with theory. Moreover, we report strong heating random fluctuations close to the beamresulting from the fluctuations of the beam intensity. We show that, close to the beam, these heating fluctuations dominate largely over the averaged heating, as predicted by the theory of heat propagation with a random source.

A thin layer of ZnO0.3deposited on a SiO2glass substrate was irradiated with a 2 MeV α microbeam. The disappearance of ZnO0.3in the neighbourhood of the beam was registered in situ. We quantitatively account for this behaviour in the framework of a very simple vaporisation model based both upon the local temperature increase resulting from the microbeam itself and upon the variation of the Zn vapour pressure with the local temperature. Other possible explanations are briefly discussed.

We have observed reproducible conductance fluctuations at low temperature in a small GaAs:Si wire driven across the Anderson transition by the application of a gate voltage. We analyse quantitatively the log-normal conductance statistics in terms of truncated quantum fluctuations. Quantum fluctuations due to small changes of the electron energy (controlled by the gate voltage) cannot develop fully due to identified geometrical fluctuations of the resistor network describing the hopping through the sample. The evolution of the fluctuations versus electron energy and magnetic field shows that the fluctuations are non-ergodic, except in the critical insulating region of the Anderson transition, where the localization length is larger than the distance between Si impurities. The mean magnetoconductance is in good accordance with simulations based on the Forward-Directed-Path analysis, i.e. it saturates to ln(?(H>1)/?(0)) ?1, as ?(0) decreases over orders of magnitude in the strongly localized regime. Nous avons observ? des fluctuations de conductance reproductibles dans un petit fil de GaAs:Si auquel nous avons fait passer la transition d'Anderson par application d'une tension de grille. Nous analysons quantitativement la statistique log-normale de conductance en termes de fluctuations quantiques tronqu?es. Les fluctuations quantiques dues ? de petites variations de l'?nergie des ?lectrons (contr?l?e par la tension de grille) ne peuvent pas se d?velopper compl?tement ? cause des fluctuations g?om?triques du r?seau de r?sistances associ? ? la conduction par sauts dans l'?chantillon. L'?volution des fluctuations, suivant l'?nergie des ?lectrons ou le champ magn?tique, montre que les fluctuations sont non ergodiques, sauf dans le domaine d'isolant critique de la transition d'Anderson o? la longueur de localisation est grande devant la distance entre impuret?s de Si. La magn?toconductance moyenne est en bon accord avec des simulations fond?es sur l'analyse de ?chemins dirig?s", c'est-?-dire qu'elle sature ? ln (?(H>1)/?(0)) ?1 pour ?(0) variant sur plusieurs ordres de grandeur dans le r?gime fortement localis?.