1,524 research outputs found
A rigorous path integral for quantum spin using flat-space Wiener regularization
Adapting ideas of Daubechies and Klauder [J. Math. Phys. {\bf 26} (1985)
2239] we derive a rigorous continuum path-integral formula for the semigroup
generated by a spin Hamiltonian. More precisely, we use spin-coherent vectors
parametrized by complex numbers to relate the coherent representation of this
semigroup to a suitable Schr\"odinger semigroup on the Hilbert space
of Lebesgue square-integrable functions on the Euclidean plane . The
path-integral formula emerges from the standard Feynman-Kac-It\^o formula for
the Schr\"odinger semigroup in the ultra-diffusive limit of the underlying
Brownian bridge on . In a similar vein, a path-integral formula can be
constructed for the coherent representation of the unitary time evolution
generated by the spin Hamiltonian.Comment: revised versio
Quasi-classical path integral approach to supersymmetric quantum mechanics
{}From Feynman's path integral, we derive quasi-classical quantization rules
in supersymmetric quantum mechanics (SUSY-QM). First, we derive a SUSY
counterpart of Gutzwiller's formula, from which we obtain the quantization rule
of Comtet, Bandrauk and Campbell when SUSY is good. When SUSY is broken, we
arrive at a new quantization formula, which is found as good as and even
sometime better than the WKB formula in evaluating energy spectra for certain
one-dimensional bound state problems. The wave functions in the stationary
phase approximation are also derived for SUSY and broken SUSY cases. Insofar as
a broken SUSY case is concerned, there are strong indications that the new
quasi-classical approximation formula always overestimates the energy
eigenvalues while WKB always underestimates.Comment: 13 pages + 5 figures, complete paper submitted as postscript file, to
appear in Phys. Rev.
Polarisation dependence of magnetic Bragg scattering in YMnO
The polarisation dependence of the intensity of elastic magnetic scattering
from \ymno\ single crystals has been measured at 25 K in magnetic fields
between 1 and 9 T. A significant polarisation dependence was observed in the
intensities of magnetic satellite reflections, propagation vector
\pv=0.5,0,0.25 measured with both the [100] and [010] axes parallel to the
common polarisation and applied field direction. The intensity asymmetries
observed in sets of orthorhombicly equivalent reflections show systematic
relationships which allow the phase relationship between different components
of their magnetic interaction vectors to be determined. They fix the
orientation relationships between the small and moments on the \mnfp\
and \mntp\ sub-lattices and lend support to the structure reported by Kim et
al. It was found that that which suggests
that there is a small modulation of the nuclear structure which has the same
wave-vector as the magnetic modulation leading to a small nuclear structure
factor for the satellite reflections. The differences observed indicate shifts in the atomic positions of order 0.005 \AA
Interpretation of a Unified Theory of Gravitation and Symmetry Breaking
The formalism of Moen and Moffat is interpreted as a Yang-Mills theory set in a space-time generally endowed with curvature and torsion
Constructing Dirac linear fermions in terms of non-linear Heisenberg spinors
We show that the massive (or massless) neutrinos can be described as special
states of Heisenberg nonlinear spinors. As a by-product of this decomposition a
particularly attractive consequence appears: the possibility of relating the
existence of only three species of mass-less neutrinos to such internal
non-linear structure. At the same time it allows the possibility that neutrino
oscillation can occurs even for massless neutrinos
Supersymmetric quantum mechanics based on higher excited states
We generalize the formalism and the techniques of the supersymmetric (susy)
quantum mechanics to the cases where the superpotential is generated/defined by
higher excited eigenstates. The generalization is technically almost
straightforward but physically quite nontrivial since it yields an infinity of
new classes of susy-partner potentials, whose spectra are exactly identical
except for the lowest m+1 states, if the superpotential is defined in terms of
the (m+1)-st eigenfunction, with m=0 reserved for the ground state. It is shown
that in case of the infinite 1-dim potential well nothing new emerges (the
partner potential is still of P\"oschl-Teller type I, for all m), whilst in
case of the 1-dim harmonic oscillator we get a new class of infinitely many
partner potentials: for each m the partner potential is expressed as the sum of
the quadratic harmonic potential plus rational function, defined as the
derivative of the ratio of two consecutive Hermite polynomials. These partner
potentials of course have m singularities exactly at the locations of the nodes
of the generating (m+1)-st wavefunction. The susy formalism applies everywhere
between the singularities. A systematic application of the formalism to other
potentials with known spectra would yield an infinitely rich class of
"solvable" potentials, in terms of their partner potentials. If the potentials
are shape invariant they can be solved at least partially and new types of
analytically obtainable spectra are expected.
PACS numbers: 03.65.-w, 03.65.Ge, 03.65.SqComment: 15 pages LaTeX file, no figures, submitted to J. Phys. A: accepted
for publication
On the Path Integral in Imaginary Lobachevsky Space
The path integral on the single-sheeted hyperboloid, i.e.\ in -dimensional
imaginary Lobachevsky space, is evaluated. A potential problem which we call
``Kepler-problem'', and the case of a constant magnetic field are also
discussed.Comment: 16 pages, LATEX, DESY 93-14
An Effective Reduction of Critical Current for Current-Induced Magnetization Switching by a Ru Layer Insertion in an Exchange-Biased Spin-Valve
Recently it has been predicted that a spin-polarized electrical current
perpendicular-to-plane (CPP) directly flowing through a magnetic element can
induce magnetization switching through spin-momentum transfer. In this letter,
the first observation of current-induced magnetization switching (CIMS) in
exchange-biased spin-valves (ESPVs) at room temperature is reported. The ESPVs
show the CIMS behavior under a sweeping dc current with a very high critical
current density. It is demonstrated that a thin Ruthenium (Ru) layer inserted
between a free layer and a top electrode effectively reduces the critical
current densities for the CIMS. An "inverse" CIMS behavior is also observed
when the thickness of the free layer increases.Comment: 15 pages with figure
Magnetic Properties of Epitaxial and Polycrystalline Fe/Si Multilayers
Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown
via ion-beam sputtering on both glass and single-crystal substrates. High-angle
x-ray diffraction measurements show that both sets of films have narrow Fe
peaks, implying a large crystallite size and crystalline iron silicide spacer
layers. Low-angle x-ray diffraction measurements show that films grown on glass
have rougher interfaces than those grown on single-crystal substrates. The
multilayers grown on glass have a larger remanent magnetization than the
multilayers grown on single-crystal substrates. The observation of
magnetocrystalline anisotropy in hysteresis loops and peaks in x-ray
diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The
smaller remanent magnetization in Fe/Si multilayers with better layering
suggests that the remanence is not an intrinsic property.Comment: 9 pages, RevTex, 4 figures available by fax. Send email to
[email protected] for more info. Submitted to '95 MMM proceeding
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