452 research outputs found
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
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'
Quantum Hall effect in narrow graphene ribbons
The edge states in the integer quantum Hall effect are known to be
significantly affected by electrostatic interactions leading to the formation
of compressible and incompressible strips at the boundaries of Hall bars. We
show here, in a combined experimental and theoretical analysis, that this does
not hold for the quantum Hall effect in narrow graphene ribbons. In our
graphene Hall bar, which is only 60 nm wide, we observe the quantum Hall effect
up to Landau level index k=2 and show within a zero free-parameter model that
the spatial extent of the compressible and incompressible strips is of a
similar magnitude as the magnetic length. We conclude that in narrow graphene
ribbons the single-particle picture is a more appropriate description of the
quantum Hall effect and that electrostatic effects are of minor importance.Comment: RevTex, 5 pages, 4 figures (matches published version
Large magnetoresistance effect due to spin-injection into a non-magnetic semiconductor
A novel magnetoresistance effect, due to the injection of a spin-polarized
electron current from a dilute magnetic into a non-magnetic semiconductor, is
presented. The effect results from the suppression of a spin channel in the
non-magnetic semiconductor and can theoretically yield a positive
magnetoresistance of 100%, when the spin flip length in the non-magnetic
semiconductor is sufficiently large. Experimentally, our devices exhibit up to
25% magnetoresistance.Comment: 3 figures, submitted for publicatio
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
Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)
We have investigated the growth by molecular-beam epitaxy of the II-VI
diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates.
The growth start has been optimized by using low-temperature epitaxy. Surface
properties were assessed by Nomarski and scanning electron microscopy. Optical
properties of (Zn,Mn)Se have been studied by photoluminescence and a giant
Zeeman splitting of up to 30 meV has been observed. Our observations indicate a
high crystalline quality of the epitaxial films.Comment: To be published in Applied Physics Letter
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