Low-field diffusion magneto-thermopower of a high mobility two-dimensional electron gas

The low magnetic field diffusion thermopower of a high mobility GaAs-heterostructure has been measured directly on an electrostatically defined micron-scale Hall-bar structure at low temperature (T = 1.6 K) in the low magnetic field regime (B < 1.2 T) where delocalized quantum Hall states do not influence the measurements. The sample design allowed the determination of the field dependence of the thermopower both parallel and perpendicular to the temperature gradient, denoted respectively by Sxx (longitudinal thermopower) and Syx (Nernst-Ettinghausen coefficient). The experimental data show clear oscillations in Sxx and Syx due to the formation of Landau levels for 0.3 T < B < 1.2 T and reveal that Syx is approximately 120 times larger than Sxx at a magnetic field of 1 T, which agrees well with the theoretical prediction.Comment: 4 pages, 4 figure

Lattice constant variation and complex formation in zincblende Gallium Manganese Arsenide

We perform high resolution X-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low temperature molecular beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate temperatures of 220 and 270 degrees C the extrapolated relaxed lattice constant of Zincblende MnAs is 0.590 nm and 0.598 nm respectively. This is in contrast to low temperature GaAs, for which the lattice constant decreases with increasing substrate temperature.Comment: pdf onl

Thermo-Electric Properties of Quantum Point Contacts

I. Introduction II. Theoretical background (Landauer-Buttiker formalism of thermo-electricity, Quantum point contacts as ideal electron waveguides, Saddle-shaped potential) III. Experiments (Thermopower, Thermal conductance, Peltier effect) IV. ConclusionsComment: #4 of a series of 4 legacy reviews on QPC'

Zero field spin polarization in a 2D paramagnetic resonant tunneling diode

We study I-V characteristics of an all-II-VI semiconductor resonant tunneling diode with dilute magnetic impurities in the quantum well layer. Bound magnetic polaron states form in the vicinity of potential fluctuations at the well interface while tunneling electrons traverse these interface quantum dots. The resulting microscopic magnetic order lifts the degeneracy of the resonant tunneling states. Although there is no macroscopic magnetization, the resulting resonant tunneling current is highly spin polarized at zero magnetic field due to the zero field splitting. Detailed modeling demonstrates that the local spin polarization efficiency exceeds 90% without an external magnetic field.Comment: 7 pages, 10 figures (including supplementary information

Residual strain in free-standing CdTe nanowires overgrown with HgTe

We investigate the crystal properties of CdTe nanowires overgrown with HgTe. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) confirm, that the growth results in a high ensemble uniformity and that the individual heterostructures are single-crystalline, respectively. We use high-resolution X-ray diffraction (HRXRD) to investigate strain, caused by the small lattice mismatch between the two materials. We find that both CdTe and HgTe show changes in lattice constant compared to the respective bulk lattice constants. The measurements reveal a complex strain pattern with signatures of both uniaxial and shear strains present in the overgrown nanowires