60 research outputs found
Electronic transport through nuclear-spin-polarization-induced quantum wire
Electron transport in a new low-dimensional structure - the nuclear spin
polarization induced quantum wire (NSPI QW) is theoretically studied. In the
proposed system the local nuclear spin polarization creates the effective
hyperfine field which confines the electrons with the spins opposite to the
hyperfine field to the regions of maximal nuclear spin polarization. The
influence of the nuclear spin relaxation and diffusion on the electron energy
spectrum and on the conductance of the quantum wire is calculated and the
experimental feasibility is discussed.Comment: 5 pages, 4 figure
Spins, charges and currents at Domain Walls in a Quantum Hall Ising Ferromagnet
We study spin textures in a quantum Hall Ising ferromagnet. Domain walls
between ferro and unpolarized states at are analyzed with a functional
theory supported by a microscopic calculation. In a neutral wall, Hartree
repulsion prevents the appearance of a fan phase provoked by a negative
stiffness. For a charged system, electrons become trapped as solitons at the
domain wall. The size and energy of the solitons are determined by both Hartree
and spin-orbit interactions. Finally, we discuss how electrical transport takes
place through the domain wall.Comment: 4 pages, 3 figures include
Mechanism, dynamics, and biological existence of multistability in a large class of bursting neurons
Multistability, the coexistence of multiple attractors in a dynamical system,
is explored in bursting nerve cells. A modeling study is performed to show that
a large class of bursting systems, as defined by a shared topology when
represented as dynamical systems, is inherently suited to support
multistability. We derive the bifurcation structure and parametric trends
leading to multistability in these systems. Evidence for the existence of
multirhythmic behavior in neurons of the aquatic mollusc Aplysia californica
that is consistent with our proposed mechanism is presented. Although these
experimental results are preliminary, they indicate that single neurons may be
capable of dynamically storing information for longer time scales than
typically attributed to nonsynaptic mechanisms.Comment: 24 pages, 8 figure
Gate-Controlled Electron Spin Resonance in a GaAs/AlGaAs Heterostructure
The electron spin resonance (ESR) of two-dimensional electrons is
investigated in a gated GaAs/AlGaAs heterostructure. We found that the ESR
resonance frequency can be turned by means of a gate voltage. The front and
back gates of the heterostructure produce opposite g-factor shift, suggesting
that electron g-factor is being electrostatically controlled by shifting the
equilibrium position of the electron wave function from one epitaxial layer to
another with different g-factors
Measurements of the Composite Fermion masses from the spin polarization of 2-D electrons in the region
Measurements of the reflectivity of a 2-D electron gas are used to deduce the
polarization of the Composite Fermion hole system formed for Landau level
occupancies in the regime 1<\nu<2. The measurements are consistent with the
formation of a mixed spin CF system and allow the density of states or
`polarization' effective mass of the CF holes to be determined. The mass values
at \nu=3/2 are found to be ~1.9m_{e} for electron densities of 4.4 x 10^{11}
cm^{-2}, which is significantly larger than those found from measurements of
the energy gaps at finite values of effective magnetic field.Comment: 4 pages, 3 fig
Spin Bottlenecks in the Quantum Hall Regim
We present a theory of time-dependent tunneling between a metal and a
partially spin-polarized two-dimensional electron system (2DES). We find that
the leakage current which flows to screen an electric field between the metal
and the 2DES is the sum of two exponential contributions whose relative weights
depend on spin-dependent tunneling conductances, on quantum corrections to the
electrostatic capacitance of the tunnel junction, and on the rate at which the
2DES spin-polarization approaches equilibrium. For high-mobility and
homogeneous 2DES's at Landau level filling factor , we predict a ratio
of the fast and slow leakage rates equal to where is the number
of reversed spins in the skyrmionic elementary charged excitations.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Functional Integration Approach to Hysteresis
A general formulation of scalar hysteresis is proposed. This formulation is
based on two steps. First, a generating function g(x) is associated with an
individual system, and a hysteresis evolution operator is defined by an
appropriate envelope construction applied to g(x), inspired by the overdamped
dynamics of systems evolving in multistable free energy landscapes. Second, the
average hysteresis response of an ensemble of such systems is expressed as a
functional integral over the space G of all admissible generating functions,
under the assumption that an appropriate measure m has been introduced in G.
The consequences of the formulation are analyzed in detail in the case where
the measure m is generated by a continuous, Markovian stochastic process. The
calculation of the hysteresis properties of the ensemble is reduced to the
solution of the level-crossing problem for the stochastic process. In
particular, it is shown that, when the process is translationally invariant
(homogeneous), the ensuing hysteresis properties can be exactly described by
the Preisach model of hysteresis, and the associated Preisach distribution is
expressed in closed analytic form in terms of the drift and diffusion
parameters of the Markovian process. Possible applications of the formulation
are suggested, concerning the interpretation of magnetic hysteresis due to
domain wall motion in quenched-in disorder, and the interpretation of critical
state models of superconducting hysteresis.Comment: 36 pages, 9 figures, to be published on Phys. Rev.
4D Lorentz Electron Microscopy Imaging: Magnetic Domain Wall Nucleation, Reversal, and Wave Velocity
Observation of isotropic dipolar to uniaxial dipolar crossover in gadolinium
Extensive high-resolution magnetic-susceptibility (χ ) measurements have been
performed along the c axis (easy direction of magnetization) of a high-purity gadolinium single
crystal in the reduced temperature range 5.1×10-5<~ε
=(T-TC)/TC≤1.2×10-1. The results of an elaborate data analysis
permit the first accurate determination of asymptotic critical exponent for χ and unambiguously
demonstrate that the asymptotic critical behavior of gadolinium is that of a uniaxial dipolar (UD)
ferromagnet. In addition, present results using existing data on critical spin dynamics provide
conclusive evidence for the occurrence of UD→isotropic dipolar (ID)→ Gaussian crossovers.
While the UD→ID crossover is sharply defined and occurs at ε
COUD→ID=2.05(10)×10-3, the ID?Gaussian crossover proceeds without
the (theoretically predicted) intervening isotropic short-range Heisenberg regime and takes place
over a wide temperature range
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