1,394 research outputs found
Signatures of dynamically polarized nuclear spins in all-electrical lateral spin transport devices
The effect of nuclear spins in Fe/GaAs all-electrical spin-injection devices
is investigated. At temperatures below 50 K, strong modifications of the
non-local spin signal are found that are characteristic for hyperfine coupling
between conduction electrons and dynamically polarized nuclear spins. The
perpendicular component of the nuclear Overhauser field depolarizes electron
spins near zero in-plane external magnetic field, and can suppress such
dephasing when antialigned with the external field, leading to satellite peaks
in a Hanle measurement. The features observed agree well with a Monte Carlo
simulation of the spin diffusion equation including hyperfine interaction, and
are used to study the nuclear spin dynamics and relate it to the spin
polarization of injected electrons.Comment: 6 pages, 4 figure
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
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
Transmission Line Impedance of Carbon Nanotube Thin Films for Chemical Sensing
We measure the resistance and frequency-dependent gate capacitance of carbon
nanotube (CNT) thin films in ambient, vacuum, and under low-pressure (10E-6
torr) analyte environments. We model the CNT film as an RC transmission line
and show that changes in the measured capacitance as a function of gate bias
and analyte pressure are consistent with changes in the transmission line
impedance due to changes in the CNT film resistivity alone; the electrostatic
gate capacitance of the CNT film does not depend on gate voltage or chemical
analyte adsorption. However, the CNT film resistance is enormously sensitive to
low pressure analyte exposure.Comment: 14 pages, 4 figure
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