A new protocol for an aging experiment is studied in the electron-glass phase of indium-oxide films. In this protocol, the sample is exposed to a non-Ohmic electric field F for a waiting time t(w) during which the system attempts to reach a steady state (rather than relax towards equilibrium). The relaxation of the excess conductance Delta G after Ohmic conditions are restored exhibits simple aging as long as F is not too large.

Topological insulators (TIs) hold great promise for topological quantum computation in solidstate systems. Recently, several groups reported experimental data suggesting that signatures of Majorana modes have been observed in topological insulator Josephson junctions (TIJJs). A prerequisite for the exploration of Majorana physics is to obtain a good understanding of the properties of low-energy Andreev bound states (ABS) in a material with topologically non-trivial band structure. Here, we present experimental data and a theoretical analysis demonstrating that the band structure inversion close to the surface of a TI has observable consequences for supercurrent transport in TIJJs prepared on surface-doped Bi 2 Se 3 thin films. Electrostatic carrier depletion of the film surface leads to an abrupt drop in the critical current of such devices. The effect can be understood as a relocation of low-energy ABS from a region deeper in the bulk of the material to the more strongly disordered surface which is driven by the topology of the effective band structure in the presence of surface dopants.

We present low-temperature measurements of the low-frequency 1/f noise arising from an ensemble of twolevel fluctuators in the oxide barrier of Al/AlO x /Al Josephson junctions. The fractional noise power spectrum of the critical-current and normal-state resistance have similar magnitudes and scale linearly with temperature, implying an equivalence between the two. Compiling our results and published data, we deduce the area and temperature scaling of the noise for AlO x barrier junctions. We find that the density of two-level fluctuators in the junction barrier is similar to the typical value in glassy systems. We discuss the implications and consistency with recent qubit experiments.Recent progress in superconducting qubits have resulted in longer coherence times. How far this improvement can continue depends crucially on the losses intrinsic to the Josephson junction. Qubit energy spectroscopy have revealed a density of avoided level crossings arising from the interaction of the qubit with two-level systems (TLSs) in the junction barrier 1-3 . Additionally, criticalcurrent fluctuations in Josephson junctions are known to exhibit a low-frequency 1/f α (α ∼ 1) spectrum 4,5 , which is generally understood to arise from a collection of TLSs in the tunnel barrier 6,7 . The precise microscopic origin of these TLSs and the coupling mechanisms remain relatively unknown.A survey of a variety of junction architectures from several laboratories found the low frequency 1/f criticalcurrent noise power spectral density, S Ic , to have an almost universal magnitude at T = 4.2 K 8 . By postulating a T 2 temperature dependence based on noise measurements in dc superconducting quantum interference devices (SQUID) 9 and charge qubits 10 , an almost universal noise characteristic was proposed: S Ic /I 2 c (f = 1 Hz) ≈ 1.44 × 10 −10 (T /4.2 K) 2 Hz −1 .However, results on the tunneling resistance noise 11 S Rn /R 2 n in Al/AlO x /Al shadow junctions showed a linear temperature dependence and an equivalent criticalcurrent noise magnitude at 4.2 K that is three orders of magnitude lower than previous measurements. The comparison between resistance and critical current noise is made through the Ambegaokar-Baratoff relation, I c R n = π∆/2 tanh ∆ 2kB T , where ∆, I c , R n are the superconducting energy gap, critical current, and the normal state resistance respectively. This apparent discrepancy between S Ic and S Rn led to the proposal of a Kondo-traps noise mechanism 12,13 that could account for the excess noise magnitude and T 2 dependence in the SC state.Furthermore, recent measurements of the kinetic inductance noise 14 of Al shadow junctions at T = 25 mK placed an even lower bound to the noise magnitude than previous measurements of S Ic and S Rn .To clarify the apparent discrepancy, in this Letter we present extensive measurements of both S Ic and S Rn in Al/AlO x /Al junctions, the material system most relevant in current superconducting qubits. Our measurements show an equivalence between S Ic /I 2 c and S Rn /R 2 n as expec...

We study the dependence of the glassy properties of strongly localized In2O3−x films on the sample lateral dimensions. Characteristic mesoscopic effects such as reproducible conductance fluctuations (CF) are readily observable in gated structures for sample size smaller than 100 µm measured at 4 K, and the relative amplitude of the CF decreases with the sample volume as does the flicker noise. By contrast, down to sample size of few microns, the non-equilibrium features that are attributed to the electron-glass are indistinguishable from those observed in macroscopic samples, and in particular, the relaxation dynamics is independent of sample size down to 2 µm. In addition, The usual features that characterize the electron-glass including slow-relaxation, memory effects, and full-aging behavior are all observed in the 'mesoscopic' regime, and they appear to be independent of the conductance fluctuations.

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