Tunable Supercurrent Through Semiconductor Nanowires

Nanoscale superconductor-semiconductor hybrid devices are assembled from InAs semiconductor nanowires individually contacted by aluminum-based superconductor electrodes. Below 1 K, the high transparency of the contacts gives rise to proximity-induced superconductivity. The nanowires form superconducting weak links operating as mesoscopic Josephson junctions with electrically tunable coupling. The supercurrent can be switched on/off by a gate voltage acting on the electron density in the nanowire. A variation in gate voltage induces universal fluctuations in the normal-state conductance which are clearly correlated to critical current fluctuations. The ac Josephson effect gives rise to Shapiro steps in the voltage-current characteristic under microwave irradiation.Comment: 9 pages, 3 figure

Ferroelectric Thin-Film Capacitors and Piezoelectric Switches for Mobile Communication Applications

Thin-film ferroelectric capacitors have been integrated with resistors and active functions such as ESD protection into small, miniaturized modules, which enable a board space saving of up to 80%. With the optimum materials and processes, integrated capacitors with capacitance densities of up to 100 nF/mm2 for stacked capacitors combined with breakdown voltages of 90 V have been achieved. The integration of these high-density capacitors with extremely high breakdown voltage is a major accomplishment in the world of passive components and has not yet been reported for any other passive integration technology. Furthermore, thin-film tunable capacitors based on barium strontium titanate with high tuning range and high quality factor at 1 GHz have been demonstrated. Finally, piezoelectric thin films for piezoelectric switches with high switching speed have been realized

Optical transitions in few-electron artificial atoms strongly confined in ZnO nanocrystals

We have studied the optical transitions in artificial atoms consisting of one to ten electrons occupying the conduction levels in ZnO nanocrystals. We analyzed near IR absorption spectra of assemblies of weakly coupled ZnO nanocrystals for a gradually increasing electron number and found four allowed dipole transitions with oscillator strengths in quantitative agreement with tight-binding theory. Furthermore, this spectroscopy provides the single-particle energy separation between the conduction levels of the ZnO quantum dots

Quantum Interference Effects in InAs Semiconductor Nanowires

We report quantum interference effects in InAs semiconductor nanowires strongly coupled to superconducting electrodes. In the normal state, universal conductance fluctuations are investigated as a function of the magnetic field, the temperature, the bias and the gate voltage. The results are found to be in good agreement with theoretical predictions for weakly disordered one-dimensional conductors. In the superconducting state, the fluctuation amplitude is enhanced by a factor up to similar to 1.6, which is attributed to a doubling of the charge transport via Andreev reflection. At a temperature of 4.2 K, well above the Thouless temperature, conductance fluctuations are almost entirely suppressed and the nanowire conductance exhibits anomalous quantization in steps of e(2)/h.