97 research outputs found
Current induced Spin Torque in a nanomagnet
In a nanomagnet (whose total spin S< 1000), very small polarized currents can
lead to magnetic reversal. Treating on the same footing the transport and
magnetic properties of a nanomagnet connected to magnetic leads via tunneling
barriers, we derive a closed equation for the time evolution of the
magnetization. The interplay between Coulomb blockade phenomena and magnetism
gives some additional structure to the current induced spin torque. In addition
to the possibility of stabilizing uniform spin waves, we find that the system
is highly hysteretic: up to three different magnetic states can be
simultaneously stable in one region of the parameter (magnetic field and bias
voltage) space.Comment: 5 pages, 3 figures to appear in Phys. Rev. Let
Fano resonances as a probe of phase coherence in quantum dots
In the presence of direct trajectories connecting source and drain contacts,
the conductance of a quantum dot may exhibit resonances of the Fano type. Since
Fano resonances result from the interference of two transmission pathways,
their lineshape (as described by the Fano parameter q) is sensitive to
dephasing in the quantum dot. We show that under certain circumstances the
dephasing time can be extracted from a measurement of q for a single resonance.
We also show that q fluctuates from level to level, and calculate its
probability distribution for a chaotic quantum dot. Our results are relevant to
recent experiments by Goeres et al.Comment: 4 pages, 3 figures; published versio
Magnetic Insulator-Induced Proximity Effects in Graphene: Spin Filtering and Exchange Splitting Gaps
We report on first-principles calculations of spin-dependent properties in
graphene induced by its interaction with a nearby magnetic insulator (Europium
oxide, EuO). The magnetic proximity effect results in spin polarization of
graphene orbitals by up to 24 %, together with large exchange splitting
bandgap of about 36 meV. The position of the Dirac cone is further shown to
depend strongly on the graphene-EuO interlayer. These findings point towards
the possible engineering of spin gating by proximity effect at relatively high
temperature, which stands as a hallmark for future all-spin information
processing technologies.Comment: 5 pages, 4 figure
The self-consistent quantum-electrostatic problem in strongly non-linear regime
The self-consistent quantum-electrostatic (also known as
Poisson-Schr\"odinger) problem is notoriously difficult in situations where the
density of states varies rapidly with energy. At low temperatures, these
fluctuations make the problem highly non-linear which renders iterative schemes
deeply unstable. We present a stable algorithm that provides a solution to this
problem with controlled accuracy. The technique is intrinsically convergent
including in highly non-linear regimes. We illustrate our approach with (i) a
calculation of the compressible and incompressible stripes in the integer
quantum Hall regime and (ii) a calculation of the differential conductance of a
quantum point contact geometry. Our technique provides a viable route for the
predictive modeling of the transport properties of quantum nanoelectronics
devices.Comment: 28 pages. 14 figures. Added solution to a potential failure mode of
the algorith
Current induced distortion of a magnetic domain wall
We consider the spin torque induced by a current flowing ballistically
through a magnetic domain wall. In addition to a global pressure in the
direction of the electronic flow, the torque has an internal structure of
comparable magnitude due to the precession of the electrons' spins at the
"Larmor" frequency. As a result, the profile of the domain wall is expected to
get distorted by the current and acquires a periodic sur-structure.Comment: 5 pages, 3 eps figure
Spin-transfer torque in magnetic multilayer nanopillars
We consider a quasi one-dimensional configuration consisting of two small
pieces of ferromagnetic material separated by a metallic one and contacted by
two metallic leads. A spin-polarized current is injected from one lead. Our
goal is to investigate the correlation induced between the magnetizations of
the two ferromagnets by spin-transfer torque. This torque results from the
interaction between the magnetizations and the spin polarization of the
current. We discuss the dynamics of a single ferromagnet, the extension to the
case of two ferromagnets, and give some estimates for the parameters based on
experiments.Comment: To appear in the Journal of Physics: Conference Series (Proceedings
of the International Conference on Nanoscience and Technology, Basel, 2006
Direct probing of band-structure Berry phase in diluted magnetic semiconductors
We report on experimental evidence of the Berry phase accumulated by the
charge carrier wave function in single-domain nanowires made from a
(Ga,Mn)(As,P) diluted ferromagnetic semiconductor layer. Its signature on the
mesoscopic transport measurements is revealed as unusual patterns in the
magnetoconductance, that are clearly distinguished from the universal
conductance fluctuations. We show that these patterns appear in a magnetic
field region where the magnetization rotates coherently and are related to a
change in the band-structure Berry phase as the magnetization direction
changes. They should be thus considered as a band structure Berry phase
fingerprint of the effective magnetic monopoles in the momentum space. We argue
that this is an efficient method to vary the band structure in a controlled way
and to probe it directly. Hence, (Ga,Mn)As appears to be a very interesting
test bench for new concepts based on this geometrical phase.Comment: 7 pages, 6 figure
- …