10,438 research outputs found
Influence of magnetic viscosity on domain wall dynamics under spin-polarized currents
We present a theoretical study of the influence of magnetic viscosity on
current-driven domain wall dynamics. In particular we examine how domain wall
depinning transitions, driven by thermal activation, are influenced by the
adiabatic and nonadiabatic spin-torques. We find the Arrhenius law that
describes the transition rate for activation over a single energy barrier
remains applicable under currents but with a current-dependent barrier height.
We show that the effective energy barrier is dominated by a linear current
dependence under usual experimental conditions, with a variation that depends
only on the nonadiabatic spin torque coefficient beta.Comment: 8 pages, 4 figure
Local Hall effect in hybrid ferromagnetic/semiconductor devices
We have investigated the magnetoresistance of ferromagnet-semiconductor
devices in an InAs two-dimensional electron gas system in which the magnetic
field has a sinusoidal profile. The magnetoresistance of our device is large.
The longitudinal resistance has an additional contribution which is odd in
applied magnetic field. It becomes even negative at low temperature where the
transport is ballistic. Based on the numerical analysis, we confirmed that our
data can be explained in terms of the local Hall effect due to the profile of
negative and positive field regions. This device may be useful for future
spintronic applications.Comment: 4 pages with 4 fugures. Accepted for publication in Applied Physics
Letter
Tuning the proximity effect in a superconductor-graphene-superconductor junction
We have tuned in situ the proximity effect in a single graphene layer coupled
to two Pt/Ta superconducting electrodes. An annealing current through the
device changed the transmission coefficient of the electrode/graphene
interface, increasing the probability of multiple Andreev reflections. Repeated
annealing steps improved the contact sufficiently for a Josephson current to be
induced in graphene.Comment: Accepted for publication in Phys. Rev.
Lineshape distortion in a nonlinear auto-oscillator near generation threshold: Application to spin-torque nano-oscillators
The lineshape in an auto-oscillator with a large nonlinear frequency shift in
the presence of thermal noise is calculated. Near the generation threshold,
this lineshape becomes strongly non-Lorentzian, broadened, and asymmetric. A
Lorentzian lineshape is recovered far below and far above threshold, which
suggests that lineshape distortions provide a signature of the generation
threshold. The theory developed adequately describes the observed behavior of a
strongly nonlinear spin-torque nano-oscillator.Comment: 4 pages, 3 figure
Momentum dependence of the N to Delta transition form factors
We present a new method to determine the momentum dependence of the N to
Delta transition form factors and demonstrate its effectiveness in the quenched
theory at on a lattice. We address a number of
technical issues such as the optimal combination of matrix elements and the
simultaneous overconstrained analysis of all lattice vector momenta
contributing to a given momentum transfer squared, .Comment: Talk presented at Lattice 2004 (spectrum), Fermilab, 21-26 Jun. 2004.
3 pages, 3 figures. One typo in phenomenological Ansatz correcte
Stochastic theory of spin-transfer oscillator linewidths
We present a stochastic theory of linewidths for magnetization oscillations
in spin-valve structures driven by spin-polarized currents. Starting from a
nonlinear oscillator model derived from spin-wave theory, we derive Langevin
equations for amplitude and phase fluctuations due to the presence of thermal
noise. We find that the spectral linewidths are inversely proportional to the
spin-wave intensities with a lower bound that is determined purely by
modulations in the oscillation frequencies. Reasonable quantitative agreement
with recent experimental results from spin-valve nanopillars is demonstrated.Comment: Submitted to Physical Review
QCDOC: A 10-teraflops scale computer for lattice QCD
The architecture of a new class of computers, optimized for lattice QCD
calculations, is described. An individual node is based on a single integrated
circuit containing a PowerPC 32-bit integer processor with a 1 Gflops 64-bit
IEEE floating point unit, 4 Mbyte of memory, 8 Gbit/sec nearest-neighbor
communications and additional control and diagnostic circuitry. The machine's
name, QCDOC, derives from ``QCD On a Chip''.Comment: Lattice 2000 (machines) 8 pages, 4 figure
Do Clawback Adoptions Influence Capital Investments?
We present evidence that clawback provision adoptions influence capital investment mix via managerial compensation incentives. Specifically, we find for a propensity-matched sample of 931 voluntary clawback adoptions that capital investments shift away from R&D and toward capital expenditures, and for firms with enabling liquidity toward acquisitions, consistent with clawback effects on earnings-linked compensation. Corroborating evidence confirms that these effects are positively related to performance-based pay, growth opportunities, and invariant to risk-toleration incentives, with firms adopting clawbacks also exhibiting capital over-investment. This evidence is timely given a pending SEC rule that would mandate clawbacks for all firms listing on US exchanges.postprin
Loss-resilient photonic entanglement swapping using optical hybrid states
We propose a scheme of loss-resilient entanglement swapping between two distant parties via an imperfect optical channel. In this scheme, two copies of hybrid entangled states are prepared and the continuous-variable parts propagate through lossy media. In order to perform successful entanglement swapping, several different measurement schemes are considered for the continuous-variable parts such as single-photon detection for ideal cases and a homodyne detection for practical cases. We find that the entanglement swapping using hybrid states with small amplitudes offers larger entanglement than the discrete-variable entanglement swapping in the presence of large losses. Remarkably, this hybrid scheme still offers excellent robustness of entanglement to the detection inefficiency. Thus, the proposed scheme could be used for the practical quantum key distribution in hybrid optical states under photon losses
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