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The obtained periodic magnetic-field dependences I c+(Φ/Φ0) and I c−(Φ/Φ0) of the critical current measured in opposite directions on asymmetric superconducting aluminum rings has made it possible to explain previously observed quantum oscillations of dc voltage as a result of alternating current rectification. It was found that a higher rectification efficiency of both single rings and ring systems is caused by hysteresis of the current-voltage characteristics. The asymmetry of current-voltage characteristics providing the rectification effect is due to the relative shifts of the magnetic dependences I c−(Φ/Φ0) = I c+(Φ/Φ0 + Δϕ) of the critical current measured in opposite directions. This shift means that the position of I c+(Φ/Φ0) and I c−(Φ/Φ0) minima does not correspond to n + 0.5 magnetic flux Φ quanta, which is in direct contradiction to measured Little-Parks resistance oscillations. Despite this contradiction, the amplitude I c, an(Φ/Φ0) = I c+(Φ/Φ0) − I c−(Φ/Φ0) of critical current anisotropy oscillations and its variations with temperature correspond to the expected amplitude of persistent current oscillations and its variations with temperature. [ABSTRACT FROM AUTHOR]

Little-Parks oscillations are observed in a system of 110 series-connected aluminum rings 2 μm in diameter with the use of measuring currents from 10 nA to 1 μA. The measurements show that the amplitude and character of oscillations are independent of the relation between the measuring current and the amplitude of the persistent current. By using asymmetric rings, it is demonstrated that the persistent current has a direction. This means that, in the Little-Parks experiment, the total current in one of the half-rings may be directed against the electric field. [ABSTRACT FROM AUTHOR]

Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta. [ABSTRACT FROM AUTHOR]

The paper presents the results obtained in a study of electron transport in split-gate structures prepared from heterostructures with self-organizing InAs quantum dots situated close to a two-dimensional electron gas. Coulomb oscillations of current through InAs quantum dots depending on the voltage on the gate were observed. Coulomb current oscillations persisted up to about 20 K. The Coulomb energy Δ E C = 12.5 meV corresponding to theoretical estimates for the p-states of quantum dots in our structures was determined. [ABSTRACT FROM AUTHOR]

The electron transport is studied in split-gate structures fabricated on the basis of a modulation-doped heterostructure that contains a single quantum well and self-assembled InAs quantum dots near the 2D electron gas regions. The current passing through the channel with a denumerable set of InAs quantum dots is found to exhibit Coulomb oscillations as a function of the gate voltage. The oscillations are associated with the excited p states of InAs quantum dots, which are characterized by opposite spins and caused by lifting of the spin degeneracy of the p state due to the Coulomb interaction. The Coulomb oscillations of the current are observed up to a temperature of ∼20 K. The Coulomb energy is found to be ΔEc = 12.5 meV, which agrees well with the theoretical estimates for the p states of quantum dots in the structures under study. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

In simply-connected, micron-size, aluminum thin-film structures in a perpendicular magnetic field, resistance oscillations with a period close to the quantum of magnetic flux through the area of the structure are observed. The results obtained attest to the fact that when Abrikosov vortices penetrate into a small-area superconducting film (mesoscopic superconducting film), the film behaves similarly to a Little–Parks thin-film interferometer. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]