arXiv subjects

Andreas D. Wieck

Publications and source records attributed to Andreas D. Wieck.

167 records · Page 10Linked to original sources

arXiv2007

Aharonov-Bohm oscillations in the presence of strong spin-orbit interactions

We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring structure defined by local anodic oxidation on a p-type GaAs heterostructure with strong spin-orbit interactions. Clear beating patterns observed in the raw data can be interpreted in terms of a spin geometric phase. Besides h/e oscillations, we resolve the contributions from the second harmonic of AB oscillations and also find a beating in these h/2e oscillations. A resistance minimum at B=0T, present in all gate configurations, is the signature of destructive interference of the spins propagating along time-reversed paths.

cond-mat.mes-hall↗

arXiv2005

Single-hole transistor in p-type GaAs/AlGaAs heterostructures

A single-hole transistor is patterned in a p-type, C-doped GaAs/AlGaAs heterostructure by AFM oxidation lithography. Clear Coulomb blockade resonances have been observed at T=300 mK. A charging energy of ~ 1.5 meV is extracted from Coulomb diamond measurements, in agreement with the lithographic dimensions of the dot. The absence of excited states in Coulomb diamond measurements, as well as the temperature dependence of Coulomb peak heights indicate that the dot is in the multi-level transport regime. Fluctuations in peak spacings larger than the estimated mean single-particle level spacing are observed.

cond-mat.mes-hall↗

arXiv2004

Magneto-capacitance probing of the many-particle states in InAs dots

We use frequency-dependent capacitance-voltage spectroscopy to measure the tunneling probability into self-assembled InAs quantum dots. Using an in-plane magnetic field of variable strength and orientation, we are able to obtain information on the quasi-particle wave functions in momentum space for 1 to 6 electrons per dot. For the lowest two energy states, we find a good agreement with Gaussian functions for a harmonic potential. The high energy orbitals exhibit signatures of anisotropic confinement and correlation effects.

cond-mat.other↗

arXiv1998

Quantum ballistic transport in in-plane-gate transistors showing onset of a novel ferromagnetic phase transition

We study one-dimensional transport in focused-ion-beam written in-plane-gate transistors on III-V heterostructures at moderately low temperatures at zero bias without any external magnetic field applied. In accordance with a recent proposal of A. Gold and L. Calmels, Valley- and spin-occupancy instability in the quasi-one-dimensional electron gas, Phil. Mag. Lett. 74, 33-42 (1996) and earlier experimental data, we observe plateaux in the source-drain conductivity considered as a function of the gate voltage, not only at multliples of 2e^2/h but also clearly at e^2/h, just before the channel closes to zero conductivity. This may be interpreted as a many electron effect, namely as a novel ballistic ferromagnetic ground state evading standard descriptions and theorems.

cond-mat.mes-hall↗

arXiv1998

Robustness of the quantum Hall effect, sample size versus sample topology, and quality control management of III-V molecular beam epitaxy

We measure the IQHE on macroscopic (1.5cm x 1.5cm) "quick 'n' dirty" prepared III-V heterostructure samples with van der Pauw and modified Corbino geometries at 1.3 K. We compare our results with (i) data taken on smaller specimens, among them samples with a standard Hall bar geometry, (ii) results of our numerical analysis taking inhomogenities of the 2DEG into account. Our main finding is a confirmation of the expected robustness of the IQHE which favours the development of wide plateaux for small filling factors and very large sample sizes (here with areas 10,000 times larger than in standard arrangements).

cond-mat.mes-hall↗