1,378 research outputs found
Proposal for a Topological Plasmon Spin Rectifier
We propose a device in which the spin-polarized AC plasmon mode in the
surface state of a topological insulator nanostructure induces a static spin
accumulation in a resonant, normal metal structure coupled to it. Using a
finite-difference time-domain model, we simulate this spin-pump mechanism with
drift, diffusion, relaxation, and precession in a magnetic field. This
optically-driven system can serve as a DC "spin battery" for spintronic
devices.Comment: Eq. 1 corrected; Figs 3 and 4 update
Probing confined phonon modes by transport through a nanowire double quantum dot
Strong radial confinement in semiconductor nanowires leads to modified
electronic and phononic energy spectra. We analyze the current response to the
interplay between quantum confinement effects of the electron and phonon
systems in a gate-defined double quantum dot in a semiconductor nanowire. We
show that current spectroscopy of inelastic transitions between the two quantum
dots can be used as an experimental probe of the confined phonon environment.
The resulting discrete peak structure in the measurements is explained by
theoretical modeling of the confined phonon mode spectrum, where the
piezoelectric coupling is of crucial importance.Comment: 4 pages, 4 figures; final versio
Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin injection device
The nonlocal spin resistance is measured as a function of temperature in a
Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin
injection, the spin resistance is observed up to room temperature and decays
exponentially with temperature at a rate of 0.018\,K. Post-growth
annealing at 440\,K increases the spin signal at low temperatures, but the
decay rate also increases to 0.030\,K. From measurements of the
diffusion constant and the spin lifetime in the GaAs channel, we conclude that
sample annealing modifies the temperature dependence of the spin transfer
efficiency at injection and detection contacts. Surprisingly, the spin transfer
efficiency increases in samples that exhibit minority-spin injection.Comment: 10 pages, 4 figure
Tunable effective g-factor in InAs nanowire quantum dots
We report tunneling spectroscopy measurements of the Zeeman spin splitting in
InAs few-electron quantum dots. The dots are formed between two InP barriers in
InAs nanowires with a wurtzite crystal structure grown by chemical beam
epitaxy. The values of the electron g-factors of the first few electrons
entering the dot are found to strongly depend on dot size and range from close
to the InAs bulk value in large dots |g^*|=13 down to |g^*|=2.3 for the
smallest dots. These findings are discussed in view of a simple model.Comment: 4 pages, 3 figure
Direct Measurement of the Spin-Orbit Interaction in a Two-Electron InAs Nanowire Quantum Dot
We demonstrate control of the electron number down to the last electron in
tunable few-electron quantum dots defined in catalytically grown InAs
nanowires. Using low temperature transport spectroscopy in the Coulomb blockade
regime we propose a simple method to directly determine the magnitude of the
spin-orbit interaction in a two-electron artificial atom with strong spin-orbit
coupling. Due to a large effective g-factor |g*|=8+/-1 the transition from
singlet S to triplet T+ groundstate with increasing magnetic field is dominated
by the Zeeman energy rather than by orbital effects. We find that the
spin-orbit coupling mixes the T+ and S states and thus induces an avoided
crossing with magnitude =0.25+/-0.05 meV. This allows us to
calculate the spin-orbit length 127 nm in such systems
using a simple model.Comment: 21 pages, 7 figures, including supplementary note
Universal conductance fluctuations in Dirac materials in the presence of long-range disorder
We study quantum transport in Dirac materials with a single fermionic Dirac
cone (strong topological insulators and graphene in the absence of intervalley
coupling) in the presence of non-Gaussian long-range disorder. We show, by
directly calculating numerically the conductance fluctuations, that in the
limit of very large system size and disorder strength, quantum transport
becomes universal. However, a systematic deviation away from universality is
obtained for realistic system parameters. By comparing our results to existing
experimental data on 1/f noise, we suggest that many of the graphene samples
studied to date are in a non-universal crossover regime of conductance
fluctuations.Comment: 5 pages, 3 figures. Published versio
Princess and the Pea at the nanoscale: Wrinkling and delamination of graphene on nanoparticles
Thin membranes exhibit complex responses to external forces or geometrical
constraints. A familiar example is the wrinkling, exhibited by human skin,
plant leaves, and fabrics, resulting from the relative ease of bending versus
stretching. Here, we study the wrinkling of graphene, the thinnest and stiffest
known membrane, deposited on a silica substrate decorated with silica
nanoparticles. At small nanoparticle density monolayer graphene adheres to the
substrate, detached only in small regions around the nanoparticles. With
increasing nanoparticle density, we observe the formation of wrinkles which
connect nanoparticles. Above a critical nanoparticle density, the wrinkles form
a percolating network through the sample. As the graphene membrane is made
thicker, global delamination from the substrate is observed. The observations
can be well understood within a continuum elastic model and have important
implications for strain-engineering the electronic properties of graphene.Comment: 11 pages, 8 figures. Accepted for publication in Physical Review
Single-Electron Effects in a Coupled Dot-Ring System
Aharonov-Bohm oscillations are studied in the magnetoconductance of a
micron-sized open quantum ring coupled capacitively to a Coulomb-blockaded
quantum dot. As the plunger gate of the dot is modulated and tuned through a
conductance resonance, the amplitude of the Aharonov-Bohm oscillations in the
transconductance of the ring displays a minimum. We demonstrate that the effect
is due to a single-electron screening effect, rather than to dephasing.
Aharonov-Bohm oscillations in a quantum ring can thus be used for the detection
of single charges.Comment: 5 pages, 3 figure
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