727 research outputs found
Detection of Single Spin Decoherence in a Quantum Dot via Charge Currents
We consider a quantum dot attached to leads in the Coulomb blockade regime
which has a spin 1/2 ground state. We show that by applying an ESR field to the
dot-spin the stationary current in the sequential tunneling regime exhibits a
resonance whose line width is determined by the single-spin decoherence time
T_2. The Rabi oscillations of the dot-spin are shown to induce coherent current
oscillations from which T_2 can be deduced in the time domain. We describe a
spin-inverter which can be used to pump current through a double-dot via spin
flips generated by ESR.Comment: 4 pages, 3 figure
cryoWriter: a blotting free cryo-EM preparation system with a climate jet and cover-slip injector
Electron microscopy (EM) introduced a fast and lasting change to structural and cellular biology. However, the sample preparation is still the bottleneck in the cryogenic electron microscopy (cryo-EM) workflow. Classical specimen preparation methods employ a harsh paper-blotting step, and the protein particles are exposed to a damaging air-water interface. Therefore, improved preparation strategies are urgently needed. Here, we present an amended microfluidic sample preparation method, which entirely avoids paper blotting and allows the passivation of the air-water interface during the preparation process. First, a climate jet excludes oxygen from the sample environment and controls the preparation temperature by varying the relative humidity of the grid environment. Second, the integrated "coverslip injector" allows the modulation of the air-water interface of the thin sample layer with effector molecules. We will briefly discuss the climate jet's effect on the stability and dynamics of the sample thin films. Furthermore, we will address the coverslip injector and demonstrate significant improvement in the sample quality
Spin generation away from boundaries by nonlinear transport
In several situations of interest, spin polarization may be generated far
from the boundaries of a sample by nonlinear effects of an electric current,
even when such a generation is forbidden by symmetry in the linear regime. We
present an analytically solvable model where spin accumulation results from a
combination of current gradients, nonlinearity, and cubic anisotropy. Further,
we show that even with isotropic conductivity, nonlinear effects in a low
symmetry geometry can generate spin polarization far away from boundaries.
Finally, we find that drift from the boundaries results in spin polarization
patterns that dominate in recent experiments on GaAs by Sih et al. [Phys. Rev.
Lett. 97, 096605 (2006)]
Asymmetric Quantum Shot Noise in Quantum Dots
We analyze the frequency-dependent noise of a current through a quantum dot
which is coupled to Fermi leads and which is in the Coulomb blockade regime. We
show that the asymmetric shot noise as function of frequency shows steps and
becomes super-Poissonian. This provides experimental access to the quantum
fluctuations of the current. We present an exact calculation for a single dot
level and a perturbative evaluation of the noise in Born approximation
(sequential tunneling regime but without Markov approximation) for the general
case of many levels with charging interaction.Comment: 5 pages, 2 figure
Theory of Spin Hall conductivity in n-doped GaAs
We develop a theory of extrinsic spin currents in semiconductors, resulting
from spin-orbit coupling at charged scatterers, which leads to skew scattering
and side jump contributions to the spin Hall conductance. Applying the theory
to bulk n-GaAs, without any free parameters, we find spin currents that are in
reasonable agreement with recent experiments by Kato et al. [Science 306, 1910
(2004)].Comment: 5 pages, 1 figur
Measurement efficiency and n-shot read out of spin qubits
We consider electron spin qubits in quantum dots and define a measurement
efficiency e to characterize reliable measurements via n-shot read outs. We
propose various implementations based on a double dot and quantum point contact
(QPC) and show that the associated efficiencies e vary between 50% and 100%,
allowing single-shot read out in the latter case. We model the read out
microscopically and derive its time dynamics in terms of a generalized master
equation, calculate the QPC current and show that it allows spin read out under
realistic conditions.Comment: 5 pages, 1 figur
First Impressions are More Important than Early Intervention Qualifying Broken Windows Theory in the Lab
Broken Windows: the metaphor has changed New York and Los Angeles. Yet it is far from undisputed whether the broken windows policy was causal for reducing crime. In a series of lab experiments we put two components of the theory to the test. We show that first impressions and early punishment of antisocial behaviour are independently and jointly causal for cooperativeness. The effect of good first impressions and of early vigilance cannot be explained with, but adds to, participants’ initial level of benevolence. Mere impression management is not strong enough to maintain cooperation. Cooperation stabilizes if good first impressions are combined with some risk of sanctions. Yet if we control for first impressions, early vigilance only has a small effect. The effect vanishes over time.
Out-of-plane spin polarization from in-plane electric and magnetic fields
We show that the joint effect of spin-orbit and magnetic fields leads to a
spin polarization perpendicular to the plane of a two-dimensional electron
system with Rashba spin-orbit coupling and in-plane parallel dc magnetic and
electric fields, for angle-dependent impurity scattering or nonparabolic energy
spectrum, while only in-plane polarization persists for simplified models. We
derive Bloch equations, describing the main features of recent experiments,
including the magnetic field dependence of static and dynamic responses.Comment: 5 pages and 1 figure in main text, 5 pages in appendi
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Spin generation away from boundaries by nonlinear transport
Spin polarization may be generated far from the boundaries of a sample by nonlinear effects of an electric current, in the presence of "extrinsic" spin-orbit interactions, even when such generation is forbidden in the linear regime. We present a Corbino model where spin accumulation results from a combination of current gradients, nonlinearity, and cubic anisotropy. Further, we show that even with isotropic conductivity, nonlinear effects in a low-symmetry sidearm geometry can generate spin polarization far away from boundaries. Finally, we find that drift from the boundaries dominates spin polarization patterns observed in recent experiments on GaAs by Sih et al. [Phys. Rev. Lett. 97, 096605 (2006)].Physic
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