290 research outputs found
On a possibility to construct gauge invariant quantum formulation for non-gauge classical theory
A non-gauge dynamical system depending on parameters is considered. It is
shown that these parameters can have such values that corresponding canonically
quantized theory will be gauge invariant. The equations allowing to find these
values of parameters are derived. The prescription under consideration is
applied to obtaining the equation of motion for tachyon background field in
closed bosonic string theory.Comment: 19 pages, LaTeX file, minor mistakes correcte
Current-voltage characteristics of semiconductor/ferromagnet junctions in the spin blockade regime
It was recently predicted [Phys. Rev. B 75, 193301 (2007)] that spin blockade
may develop at nonmagnetic semiconductor/perfect ferromagnet junctions when the
electron flow is directed from the semiconductor into the ferromagnet. Here we
consider current-voltage characteristics of such junctions. By taking into
account the contact resistance, we demonstrate a current stabilization effect:
by increasing the applied voltage the current density through the junction
saturates at a specific value. The transient behavior of the current density is
also investigated
Spin memristive systems
Recently, in addition to the well-known resistor, capacitor and inductor, a
fourth passive circuit element, named memristor, has been identified following
theoretical predictions. The model example used in such case consisted in a
nanoscale system with coupled ionic and electronic transport. Here, we discuss
a system whose memristive behaviour is based entirely on the electron spin
degree of freedom which allows for a more convenient control than the ionic
transport in nanostructures. An analysis of time-dependent spin transport at a
semiconductor/ferromagnet junction provides a direct evidence of memristive
behaviour. Our scheme is fundamentally different from previously discussed
schemes of memristive devices and broadens the possible range of applications
of semiconductor spintronics
Spin blockade at semiconductor/ferromagnet junctions
We study theoretically extraction of spin-polarized electrons at nonmagnetic
semiconductor/ferromagnet junctions. The outflow of majority spin electrons
from the semiconductor into the ferromagnet leaves a cloud of minority spin
electrons in the semiconductor region near the junction, forming a local
spin-dipole configuration at the semiconductor/ferromagnet interface. This
minority spin cloud can limit the majority spin current through the junction
creating a pronounced spin-blockade at a critical current. We calculate the
critical spin-blockade current in both planar and cylindrical geometries and
discuss possible experimental tests of our predictions.Comment: to be published in PR
Hall Voltage with the Spin Hall Effect
The spin Hall effect does not generally result in a charge Hall voltage. We
predict that in systems with inhomogeneous electron density in the direction
perpendicular to main current flow, the spin Hall effect is instead accompanied
by a Hall voltage. Unlike the ordinary Hall effect, we find that this Hall
voltage is quadratic in the longitudinal electric field for a wide range of
parameters accessible experimentally. We also predict spin accumulation in the
bulk and sharp peaks of spin-Hall induced charge accumulation near the edges.
Our results can be readily tested experimentally, and would allow the
electrical measurement of the spin Hall effect in non-magnetic systems and
without injection of spin-polarized electrons
Spin polarization control by electric stirring: proposal for a spintronic device
We propose a spintronic device to generate spin polarization in a mesoscopic
region by purely electric means. We show that the spin Hall effect in
combination with the stirring effect are sufficient to induce measurable spin
polarization in a closed geometry. Our device structure does not require the
application of magnetic fields, external radiation or ferromagnetic leads, and
can be implemented in standard semiconducting materials
Gravitational Interaction of Higher Spin Massive Fields and String Theory
We discuss the problem of consistent description of higher spin massive
fields coupled to external gravity. As an example we consider massive field of
spin 2 in arbitrary gravitational field. Consistency requires the theory to
have the same number of degrees of freedom as in flat spacetime and to describe
causal propagation. By careful analysis of lagrangian structure of the theory
and its constraints we show that there exist at least two possibilities of
achieving consistency. The first possibility is provided by a lagrangian on
specific manifolds such as static or Einstein spacetimes. The second
possibility is realized in arbitrary curved spacetime by a lagrangian
representing an infinite series in curvature. In the framework of string theory
we derive equations of motion for background massive spin 2 field coupled to
gravity from the requirement of quantum Weyl invariance. These equations appear
to be a particular case of the general consistent equations obtained from the
field theory point of view.Comment: 20 pages, talk by I.L. Buchbinder at the International Conference
"Geometrical Aspects of Quantum Fields", Londrina-Parana, April 2000, to be
published in the Proceedings, v2: references adde
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