2,029 research outputs found
A Scheme to Numerically Evolve Data for the Conformal Einstein Equation
This is the second paper in a series describing a numerical implementation of
the conformal Einstein equation. This paper deals with the technical details of
the numerical code used to perform numerical time evolutions from a "minimal"
set of data.
We outline the numerical construction of a complete set of data for our
equations from a minimal set of data. The second and the fourth order
discretisations, which are used for the construction of the complete data set
and for the numerical integration of the time evolution equations, are
described and their efficiencies are compared. By using the fourth order scheme
we reduce our computer resource requirements --- with respect to memory as well
as computation time --- by at least two orders of magnitude as compared to the
second order scheme.Comment: 20 pages, 12 figure
Electronic Theory for the Nonlinear Magneto-Optical Response of Transition-Metals at Surfaces and Interfaces: Dependence of the Kerr-Rotation on Polarization and on the Magnetic Easy Axis
We extend our previous study of the polarization dependence of the nonlinear
optical response to the case of magnetic surfaces and buried magnetic
interfaces. We calculate for the longitudinal and polar configuration the
nonlinear magneto-optical Kerr rotation angle. In particular, we show which
tensor elements of the susceptibilities are involved in the enhancement of the
Kerr rotation in nonlinear optics for different configurations and we
demonstrate by a detailed analysis how the direction of the magnetization and
thus the easy axis at surfaces and buried interfaces can be determined from the
polarization dependence of the nonlinear magneto-optical response, since the
nonlinear Kerr rotation is sensitive to the electromagnetic field components
instead of merely the intensities. We also prove from the microscopic treatment
of spin-orbit coupling that there is an intrinsic phase difference of
90 between tensor elements which are even or odd under magnetization
reversal in contrast to linear magneto-optics. Finally, we compare our results
with several experiments on Co/Cu films and on Co/Au and Fe/Cr multilayers. We
conclude that the nonlinear magneto-optical Kerr-effect determines uniquely the
magnetic structure and in particular the magnetic easy axis in films and at
multilayer interfaces.Comment: 23 pages Revtex, preprintstyle, 2 uuencoded figure
General Relativistic Scalar Field Models in the Large
For a class of scalar fields including the massless Klein-Gordon field the
general relativistic hyperboloidal initial value problems are equivalent in a
certain sense. By using this equivalence and conformal techniques it is proven
that the hyperboloidal initial value problem for those scalar fields has an
unique solution which is weakly asymptotically flat. For data sufficiently
close to data for flat spacetime there exist a smooth future null infinity and
a regular future timelike infinity.Comment: 22 pages, latex, AGG 1
Theory for Spin-Polarized Oscillations in Nonlinear Magneto-Optics due to Quantum Well States
Using an electronic tight-binding theory we calculate the nonlinear
magneto-optical response from an x-Cu/1Fe/Cu(001) film as a function of
frequency and Cu overlayer thickness (x=3 ... 25). We find very strong
spin-polarized quantum well oscillations in the nonlinear magneto-optical Kerr
effect (NOLIMOKE). These are enhanced by the large density of Fe states
close to the Fermi level acting as intermediate states for frequency doubling.
In good agreement with experiment we find two oscillation periods of 6-7 and 11
monolayers the latter being more pronounced.Comment: 12 pages, Revtex, 3 postscript figure
Conversion of hole states by acoustic solitons
The hole states in the valence band of a large class of semiconductors are
degenerate in the projections of angular momentum. Here we show that the
switching of a hole between the states can efficiently be realized by acoustic
solitons. The microscopic mechanism of such a state conversion is related to
the valence band splitting by local elastic strain. The conversion is studied
here for heavy holes localized at shallow and deep acceptors in silicon quantum
wells.Comment: 4 pages, 2 figure
Nonlinear Magneto-Optical Response of - and -Wave Superconductors
The nonlinear magneto-optical response of - and -wave superconductors
is discussed. We carry out the symmetry analysis of the nonlinear
magneto-optical susceptibility in the superconducting state. Due to the surface
sensitivity of the nonlinear optical response for systems with bulk inversion
symmetry, we perform a group theoretical classification of the superconducting
order parameter close to a surface. For the first time, the mixing of singlet
and triplet pairing states induced by spin-orbit coupling is systematically
taken into account. We show that the interference of singlet and triplet
pairing states leads to an observable contribution of the nonlinear
magneto-optical Kerr effect. This effect is not only sensitive to the
anisotropy of the gap function but also to the symmetry itself. In view of the
current discussion of the order parameter symmetry of High-T
superconductors, results for a tetragonal system with bulk singlet pairing for
various pairing symmetries are discussed.Comment: 21 pages (REVTeX) with 8 figures (Postscript
Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets
The spin-lattice relaxation time is a key quantity both for the
dynamical response of ferromagnets excited by laser pulses and as the speed
limit of magneto-optical recording. Extending the theory for the electron
paramagnetic resonance of magnetic impurities to spin-lattice relaxation in
ferromagnetic rare earths we calculate for Gd and find a value of
48 ps in very good agreement with time-resolved spin-polarized photoemission
experiments. We argue that the time scale for in metals is
essentially given by the spin-orbit induced magnetocrystalline anisotropy
energy.Comment: 18 pages revtex, 5 uuencoded figure
Bures distance between two displaced thermal states
The Bures distance between two displaced thermal states and the corresponding
geometric quantities (statistical metric, volume element, scalar curvature) are
computed. Under nonunitary (dissipative) dynamics, the statistical distance
shows the same general features previously reported in the literature by
Braunstein and Milburn for two--state systems. The scalar curvature turns out
to have new interesting properties when compared to the curvature associated
with squeezed thermal states.Comment: 3 pages, RevTeX, no figure
Fermi surface topology and low-lying quasiparticle structure of magnetically ordered Fe1+xTe
We report the first photoemission study of Fe1+xTe - the host compound of the
newly discovered iron-chalcogenide superconductors. Our results reveal a pair
of nearly electron- hole compensated Fermi pockets, strong Fermi velocity
renormalization and an absence of a spin-density-wave gap. A shadow hole pocket
is observed at the "X"-point of the Brillouin zone which is consistent with a
long-range ordered magneto-structural groundstate. No signature of Fermi
surface nesting instability associated with Q= pi(1/2, 1/2) is observed. Our
results collectively reveal that the Fe1+xTe series is dramatically different
from the undoped phases of the high Tc pnictides and likely harbor unusual
mechanism for superconductivity and quantum magnetic order.Comment: 5 pages, 4 Figures; Submitted to Phys. Rev. Lett. (2009
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