Probing temperature-driven flow lines in a gated two-dimensional electron gas with tunable spin-splitting.

We study the temperature flow of conductivities in a gated GaAs two-dimensional electron gas (2DEG) containing self-assembled InAs dots and compare the results with recent theoretical predictions. By changing the gate voltage, we are able to tune the 2DEG density and thus vary disorder and spin-splitting. Data for both the spin-resolved and spin-degenerate phase transitions are presented, the former collapsing to the latter with decreasing gate voltage and/or decreasing spin-splitting. The experimental results support a recent theory, based on modular symmetry, which predicts how the critical Hall conductivity varies with spin-splitting.

Andreev interferometers in a strong radio-frequency field.

We experimentally study the influence of 1-40 GHz radiation on the resistance of normal (N) mesoscopic conductors coupled to superconducting (S) loops (Andreev interferometers). At low radio-frequency (RF) amplitudes we observe the usual h/2e superconducting phase periodic resistance oscillations as a function of applied magnetic flux. We find that the oscillations acquire a π-shift with increasing RF amplitude, and consistently with this result the resistance at fixed phase is an oscillating function of the RF amplitude. The results are explained qualitatively as a consequence of two processes. The first is the modulation of the phase difference between the N/S interfaces by the RF field, with the resistance adiabatically following the phase. The second process is the change in the electron temperature caused by the RF field. From the data, the response time of the Andreev interferometer is estimated to be τ(f) < 40 ps. However there are a number of experimental features which remain unexplained; these include the drastic difference in behaviour of the resistance at ϕ = π and 0 as a function of the RF frequency and amplitude, and the existence of a 'window of transparency' where heating effects are weak enough to allow for the π-shift. A microscopic theory describing the influence of RF radiation on Andreev interferometers is required.

Quantum thermal conductance of electrons in a one-dimensional wire.

We use an electron thermometer to measure the temperature rise of approximately 2 x 10(5) electrons in a two-dimensional box, due to heat flow into the box through a ballistic one-dimensional (1D) constriction. Using a simple model we deduce the thermal conductance kappa(Vg) of the 1D constriction, which we compare to its electrical conductance characteristics; for the first four 1D subbands the heat carried by the electrons passing through the wire is proportional to its electrical conductance G(Vg). In the vicinity of the 0.7 structure this proportionality breaks down, and a plateau at the quantum of thermal conductance pi(2)k(2/B)T/3h is observed.

Andreev probe of persistent current states in superconducting quantum circuits.

Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give a continuous readout of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.

Fano factor reduction on the 0.7 conductance structure of a ballistic one-dimensional wire.

We have measured the nonequilibrium current noise in a ballistic one-dimensional wire which exhibits an additional conductance plateau at 0.7x2e(2)/h. The Fano factor shows a clear reduction on the 0.7 structure, and eventually vanishes upon applying a strong parallel magnetic field. These results provide experimental evidence that the 0.7 structure is associated with two conduction channels that have different transmission probabilities.

Adverse reactions to practolol: some observations on the possible relevence to immune mechanisms.

HLA antigen frequencies were determined in patients who had suffered adverse reaction to the beta-adrenergic blocking agent, practolol. No statistically significant differences were observed between these patients and control groups. The latter were selected to include two separate groups, normal random healthy population controls, and controls who had taken practolol with no apparent adverse effects. Patients suffering from the very severe form of reaction, sclerosing peritonitis, were analysed separately from those with other lesion e.g. ocular symptoms, but did not show any significant differences. Altered HLA antigen frequencies were observed for those control patients whose primary diagnosis was hypertension but this was considered to be due to selection bias.

Immunological abnormalities in patients who had the oculomucocutaneous syndrome associated with practolol therapy.

Patients with and without adverse reactions on practolol therapy showed altered immune responses. There was cutaneous anergy to Candida albicans and streptokinase/streptodornase antigens and depression of lymphocyte function in vitro. Anticomplementary activity and a wide range of autoantibodies were found in patients who had received practolol.