The magnetoconductance in YBa2Cu3O7−delta grain boundary Josephson junctions displays fluctuations at low temperatures of mesoscopic origin. The morphology of the junction suggests that transport occurs in narrow channels across the grain boundary line with a large Thouless energy. Nevertheless the measured fluctuation amplitude decreases quite slowly when increasing the voltage up to values about 20 times the Thouless energy, of the order of the nominal superconducting gap. Our findings show the coexistence of supercurrent and quasiparticle current in the junction conduction even at high nonequilibrium conditions. Model calculations confirm the reduced role of quasiparticle relaxation at temperatures up to 3 K.

Magneto-fluctuations of the normal resistance R-N have been reproducibly observed in YBa2Cu3O7-delta biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line, occurring even in the presence of large voltage drops. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in high critical temperature superconductors (HTS) and of the dissipation mechanisms are discussed. (c) 2007 Elsevier Ltd. All rights reserved.

We report a comparative investigation of the magnetic response of long channel AlGaN/AlN/GaN heterostructures (Hall-field effect transistor devices) grown on three different semi-insulating templates on silicon and sapphire. From Hall effect measurements conducted up to 573 K (300 degrees C), we find that some of these specific devices can be used as magnetic sensors in a large temperature range (similar to 600 degrees C) with a magnetic sensitivity close to 60 V/A T and a small thermal drift. On the best sample, between liquid helium temperature and 300 degrees C, the average value of the thermal drift is only -7 ppm/degrees C. (C) 2008 American Institute of Physics.

Using finite element analysis, we have calculated the Hall voltage of gated Hall sensors in the temperature range (−55 °C, 125 °C). We investigated how both the sensor shape and the external connections influence the Hall voltage and its thermal drift. The numerical results are in excellent agreement with the experimental measurements. By contrast, we checked that simplified analytical methods lead to a large numerical error, which is not acceptable in these sensors devoted to metrological applications. In particular, it is found that the thermal drift in the Hall voltage can be canceled for a current of the order of 300 µA, a much higher value than that predicted by the corresponding analytical calculations.

We present a low temperature magnetoconductance study of a submicron hall bar made from an AlGaAs/InGaAs/GaAs heterostructure. Experiments were performed at very low temperature (120 mK), with a magnetic field ranging from OT to 13.5 T. In the presence of a quantizing magnetic field, at the transition between two quantized Hall plateaus, a succession of sharp peaks is detected in the Hall signal RH and in the longitudinal resistance R-L. The peaks appearing on the high-v side of the R-L transition appear to be different from the peaks appearing on the low-v side. They mainly differ by their temperature dependence. On the high-v side of the RL transition, the temperature evolution of the peaks is typical for resonant tunneling through a single state in one of the antidots that are progressively formed when the initially occupied LL is emptied. On the low v of the transition, by contrast, the temperature dependence is different. This may be related to the asymmetry of the density of states, or to additional inelastic processes.