The magnetotransport of GaAs/InAs core/shell nanowires contacted by two superconducting Nb electrodes is investigated, where the InAs shell forms a tube-like conductive channel around the highly resistive GaAs core. By applying a magnetic field along the nanowire axis, regular magnetoconductance oscillations with an amplitude in the order of e(2)/h are observed. The oscillation amplitude is found to be larger by 2 orders of magnitude compared to the measurements of a reference sample with normal metal contacts. For the Nb-contacted core/shell nanowire the oscillation period corresponds to half a flux quantum Φ0/2 = h/2e in contrast to the period of Φ0 of the reference sample. The strongly enhanced magnetoconductance oscillations are explained by phase-coherent resonant Andreev reflections at the Nb-core/shell nanowire interface.

We study the impact of the direction of magnetic flux on the electron motion in GaAs/InAs core/shell nanowires. At small tilt angles, when the magnetic field is aligned nearly parallel to the nanowire axis, we observe Aharonov–Bohm type h/e flux periodic magnetoconductance oscillations. These are attributed to transport via angular momentum states, formed by electron waves within the InAs shell. With increasing tilt of the nanowire in the magnetic field, the flux periodic magnetoconductance oscillations disappear. Universal conductance fluctuations are observed for all tilt angles, however with increasing amplitudes for large tilt angles. We record this evolution of the electron propagation from a circling motion around the core to a diffusive transport through scattering loops and give explanations for the observed different transport regimes separated by the magnetic field orientation.

Hollow InAs nanowires are produced from GaAs/InAs core/shell nanowires by wet chemical etching of the GaAs core. At room temperature, the resistivity of several nanowires is measured before and after removal of the GaAs core. The observed change in resistivity is explained by simulating the electronic states in both structures. At cryogenic temperatures, quantum transport in hollow InAs nanowires is studied. Flux periodic conductance oscillations are observed when the magnetic field is oriented parallel to the nanowire axis.

We investigate a hybrid metallic island / single dopant electron pump based on fully-depleted silicon on insulator technology. Electron transfer between the central metallic island and the leads is controlled by resonant tunneling through single phosphorus dopants in the barriers. Top gates above the barriers are used to control the resonance conditions. Applying radio frequency signals to the gates, non-adiabatic quantized electron pumping is achieved. A simple deterministic model is presented and confirmed by comparing measurements with simulations.Accurate clocked control and transport of single electrons (SE) is a prerequisite for both the emerging field of electron quantum optics 1 and the upcoming introduction of the quantum ampere by fixing the elementary charge e. 2 Transferring an integer number of electrons N in each cycle of a drive with frequency f generates a current I = N ef . Several approaches to clocked SE transport have been made 3 of which tunable-barrier SE pumps are especially promising to reach sufficiently large currents at high accuracy for metrological needs. 4 So far, GaAs based devices achieved the highest verified accuracy at large output currents, 5-7 however a high magnetic field and sub-kelvin temperature are required for accurate operation. SE pumps made from silicon are promising candidates for less demanding operation requirements and even higher operation frequency 8 and have been realized using both adiabatic 9 and non-adiabatic 8,10 pumping schemes. They benefit from mature CMOS technology with the potential of circuit integration, e.g. on chip drive electronics 11 or the charge detectors 12,13 needed for a self-referenced quantized current source. 14,15 Additionally, CMOS technology offers excellent control of doping, opening the possibility to utilize the large addition energies of single dopants for single-electron control with a potential of increased accuracy. Up to now, the dopant or trap was used as the main quantum dot of a SE pump. [16][17][18][19] In this letter a new device scheme is examined: Single dopant states located in the barriers are used to control the tunnel coupling of a small metallic island to source and drain. While in other works similar states in barriers were an unwanted side-effect, 20 here we actively utilize these states to perform SE pumping.The investigated device is produced in a fully CMOScompatible process using both deep UV and electron beam lithography. It is based on a silicon on insulator wafer with 145 nm of SiO 2 , where the bulk silicon layer

Low-temperature transport in nanowires is accompanied by phase-coherent effects, which are observed as modulation of the conductance in an external magnetic field. In the GaAs/InAs core/shell nanowires investigated here, these are h/e flux periodic oscillations in a magnetic field aligned parallel to the nanowire axis and aperiodic universal conductance fluctuations in a field aligned perpendicularly to the nanowire axis. Both electron interference effects are used to analyse the phase coherence of the system. Temperature-dependent measurements are carried out, in order to derive the phase coherence lengths in the cross-sectional plane as well as along the nanowire sidewalls. It is found that these values show a strong anisotropy, which can be explained by the crystal structure of the GaAs/InAs core/shell nanowire. For nanowires with a radius as low as 45 nm, flux periodic oscillations were observed up to a temperature of 55 K.