1,200 research outputs found
Shuttling of Spin Polarized Electrons in Molecular Transistors
Shuttling of electrons in single-molecule transistors with magnetic leads in
the presence of an external magnetic field is considered theoretically. For a
current of partially spin-polarized electrons a shuttle instability is
predicted to occur for a finite interval of external magnetic field strengths.
The lower critical magnetic field is determined by the degree of spin
polarization and it vanishes as the spin polarization approaches 100%. The
feasibility of detecting magnetic shuttling in a -based molecular
transistor with magnetic (Ni) electrodes is discussed [A.~N.~Pasupathy et al.,
Science 306, 86 (2004)].Comment: Submitted to a special issue of "Synthetic Metals" to appear in March
201
Mechanically Induced Thermal Breakdown in Magnetic Shuttle Structures
A theory of a thermally induced single-electron "shuttling" instability in a
magnetic nanomechanical device subject to an external magnetic field is
presented in the Coulomb blockade regime of electron transport. The model
magnetic shuttle device considered comprises a movable metallic grain suspended
between two magnetic leads, which are kept at different temperatures and
assumed to be fully spin polarized with antiparallel magnetizations. For a
given temperature difference shuttling is found to occur for a region of
external magnetic fields between a lower and an upper critical field strength,
which separate the shuttling regime from normal small-amplitude "vibronic"
regimes. We find that (i) the upper critical magnetic field saturates to a
constant value in the high temperature limit and that the shuttle instability
domain expands with a decrease of the temperature, (ii) the lower critical
magnetic field depends not only on the temperature independent phenomenological
friction coefficient used in the model but also on intrinsic friction (which
vanishes in the high temperature limit) caused by magnetic exchange forces and
electron tunneling between the quantum dot and the leads. The feasibility of
using thermally driven magnetic shuttle systems to harvest thermal breakdown
phenomena is discussed.Comment: 9 pages, 2 figure
Umklapp-Assisted Electron Transport Oscillations in Metal Superlattices
We consider a superlattice of parallel metal tunnel junctions with a
spatially non-homogeneous probability for electrons to tunnel. In such
structures tunneling can be accompanied by electron scattering that conserves
energy but not momentum. In the special case of a tunneling probability that
varies periodically with period in the longitudinal direction, i.e.,
perpendicular to the junctions, electron tunneling is accompanied by "umklapp"
scattering, where the longitudinal momentum changes by a multiple of . We
predict that as a result a sequence of metal-insulator transitions can be
induced by an external electric- or magnetic field as the field strength is
increased.Comment: 5 pages, 3 figure
Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts
We consider the electrical current through a magnetic point contact in the
limit of a strong inelastic scattering of electrons. In this limit local Joule
heating of the contact region plays a decisive role in determining the
transport properties of the point contact. We show that if an applied constant
bias voltage exceeds a critical value, the stationary state of the system is
unstable, and that periodic, non-harmonic oscillations in time of both the
electrical current through the contact and the local temperature in the contact
region develop spontaneously. Our estimations show that the necessary
experimental conditions for observing such oscillations with characteristic
frequencies in the range Hz can easily be met. We also show a
possibility to manipulate upon the magnetization direction of a magnetic grain
coupled through a point contact to a bulk ferromagnetic by exciting the
above-mentioned thermal-electric oscillations.Comment: 9 pages, 6 figures, submitted to Physical Review
Nanomechanics of a magnetic shuttle device
We show that self sustained mechanical vibrations in a model magnetic shuttle device can be driven by both the charge and the spin accumulated on the movable central island of the device. Different scenarios for how spin- and charge-induced shuttle instabilities may develop are discussed and shown to depend on whether there is a Coulomb blockade of tunneling or not. The crucial role of electronic spin flips in a magnetically driven shuttle is established and shown to cause giant magnetoresistance and dynamic magnetostriction effects
Homotopy types of stabilizers and orbits of Morse functions on surfaces
Let be a smooth compact surface, orientable or not, with boundary or
without it, either the real line or the circle , and
the group of diffeomorphisms of acting on by the rule
, where and .
Let be a Morse function and be the orbit of under this
action. We prove that for , and
except for few cases. In particular, is aspherical, provided so is .
Moreover, is an extension of a finitely generated free abelian
group with a (finite) subgroup of the group of automorphisms of the Reeb graph
of .
We also give a complete proof of the fact that the orbit is tame
Frechet submanifold of of finite codimension, and that the
projection is a principal locally trivial -fibration.Comment: 49 pages, 8 figures. This version includes the proof of the fact that
the orbits of a finite codimension of tame action of tame Lie group on tame
Frechet manifold is a tame Frechet manifold itsel
Large-scale structure formation in cosmology with classical and tachyonic scalar fields
The evolution of scalar perturbations is studied for 2-component
(non-relativistic matter and dark energy) cosmological models at the linear and
non-linear stages. The dark energy is assumed to be the scalar field with
either classical or tachyonic Lagrangian and constant equation-of-state
parameter w. The fields and potentials were reconstructed for the set of
cosmological parameters derived from observations. The comparison of the
calculated within these models and experimental large-scale structure
characteristics is made. It is shown that for w=const such analysis can't
remove the existing degeneracy of the dark energy models.Comment: 15 pages, 5 figures, text corrected, references added, accepted by
Kinematics and Physics of Celestial Bodie
Electronic spin working mechanically
A single-electron tunneling (SET) device with a nanoscale central island that
can move with respect to the bulk source- and drain electrodes allows for a
nanoelectromechanical (NEM) coupling between the electrical current through the
device and mechanical vibrations of the island. Although an electromechanical
"shuttle" instability and the associated phenomenon of single-electron
shuttling were predicted more than 15 years ago, both theoretical and
experimental studies of NEM-SET structures are still carried out. New
functionalities based on quantum coherence, Coulomb correlations and coherent
electron-spin dynamics are of particular current interest. In this article we
present a short review of recent activities in this area.Comment: 17 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1303.074
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