312 research outputs found
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
Focusing of Spin Polarization in Semiconductors by Inhomogeneous Doping
We study the evolution and distribution of non-equilibrium electron spin
polarization in n-type semiconductors within the two-component drift-diffusion
model in an applied electric field. Propagation of spin-polarized electrons
through a boundary between two semiconductor regions with different doping
levels is considered. We assume that inhomogeneous spin polarization is created
locally and driven through the boundary by the electric field. The electric
field distribution and spin polarization distribution are calculated
numerically. We show that an initially created narrow region of spin
polarization can be further compressed and amplified near the boundary. Since
the boundary involves variation of doping but no real interface between two
semiconductor materials, no significant spin-polarization loss is expected. The
proposed mechanism will be therefore useful in designing new spintronic
devices
Persistent and radiation-induced currents in distorted quantum rings
Persistent and radiation-induced currents in distorted narrow quantum rings
are theoretically investigated. We show that ring distorsions can be described
using a geometrical potential term. We analyse the effect of this term on the
current induced by a magnetic flux (persistent current) and by a polarized
coherent electromagnetic field (radiation-induced current). The strongest
effects in persistent currents are observed for distorted rings with a small
number of electrons. The distortion smoothes the current oscillations as a
function of the magnetic flux and changes the temperature dependence of the
current amplitude. For radiation-induced currents, the distortion induces an ac
component in the current and affects its dependence on the radiation frequency
and intensity
Lagrange formalism of memory circuit elements: classical and quantum formulations
The general Lagrange-Euler formalism for the three memory circuit elements,
namely, memristive, memcapacitive, and meminductive systems, is introduced. In
addition, {\it mutual meminductance}, i.e. mutual inductance with a state
depending on the past evolution of the system, is defined. The Lagrange-Euler
formalism for a general circuit network, the related work-energy theorem, and
the generalized Joule's first law are also obtained. Examples of this formalism
applied to specific circuits are provided, and the corresponding Hamiltonian
and its quantization for the case of non-dissipative elements are discussed.
The notion of {\it memory quanta}, the quantum excitations of the memory
degrees of freedom, is presented. Specific examples are used to show that the
coupling between these quanta and the well-known charge quanta can lead to a
splitting of degenerate levels and to other experimentally observable quantum
effects
Air ions induced aerosol sensing by eye-safe LIDAR
Low concentrations aerosols quantification is rather challenging for LIDAR
instruments due to eye-safety restrictions so high energy pulses cannot be
utilized to improve the sensitivity. Highly sensitive but eye-save LIDAR has
been developed for the quantification of the water droplet aerosol which was
induced by air ions. Few days sensing of aerosols in closed tunnel revealed a
strong correlation between air optical transparency (LIDAR measurements) and
concentrations of positive/negative ions (ion counter Sapphir 3-M). The
correlation coefficient was observed to be almost unity for the air
transparency signal and air ions unipolarity coefficient. High sensitivity of
the water droplet aerosol quantification makes the developed eye-safe LIDAR a
perspective instrument for space resolved measurements of the air ions
distribution. Space and time resolved measurements of air ions exhalation can
be a new instrument for tectonic activity study including new earthquake
forecasting indicators search
Effect of Spin-Orbit Interaction and In-Plane Magnetic Field on the Conductance of a Quasi-One-Dimensional System
We study the effect of spin-orbit interaction and in-plane effective magnetic
field on the conductance of a quasi-one-dimensional ballistic electron system.
The effective magnetic field includes the externally applied field, as well as
the field due to polarized nuclear spins. The interplay of the spin-orbit
interaction with effective magnetic field significantly modifies the band
structure, producing additional sub-band extrema and energy gaps, introducing
the dependence of the sub-band energies on the field direction. We generalize
the Landauer formula at finite temperatures to incorporate these special
features of the dispersion relation. The obtained formula describes the
conductance of a ballistic conductor with an arbitrary dispersion relation.Comment: will appear in Physical Review
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