10,762 research outputs found
Ultrafast Quenching of the Exchange Interaction in a Mott Insulator
We investigate how fast and how effective photocarrier excitation can modify
the exchange interaction in the prototype Mott-Hubbard
insulator. We demonstrate an ultrafast quenching of both by
evaluating exchange integrals from a time-dependent response formalism and by
explicitly simulating laser-induced spin precession in an antiferromagnet that
is canted by an external magnetic field. In both cases, the electron dynamics
is obtained from nonequilibrium dynamical mean-field theory. We find that the
modified emerges already within a few electron hopping times
after the pulse, with a reduction that is comparable to the effect of chemical
doping.Comment: 8 pages, 4 figure
Ultrafast and reversible control of the exchange interaction in Mott insulators
The strongest interaction between microscopic spins in magnetic materials is
the exchange interaction . Therefore, ultrafast control of
holds the promise to control spins on ultimately fast timescales.
We demonstrate that time-periodic modulation of the electronic structure by
electric fields can be used to reversibly control on ultrafast
timescales in extended antiferromagnetic Mott insulators. In the regime of weak
driving strength, we find that can be enhanced and reduced for
frequencies below and above the Mott gap, respectively. Moreover, for strong
driving strength, even the sign of can be reversed and we show
that this causes time reversal of the associated quantum spin dynamics. These
results suggest wide applications, not only to control magnetism in condensed
matter systems, for example, via the excitation of spin resonances, but also to
assess fundamental questions concerning the reversibility of the quantum
many-body dynamics in cold atom systems.Comment: 9 pages, 4 figure
Nanoscale Suppression of Magnetization at Atomically Assembled Manganite Interfaces
Using polarized X-rays, we compare the electronic and magnetic properties of
a La(2/3)Sr(1/3)MnO(3)(LSMO)/SrTiO(3)(STO) and a modified
LSMO/LaMnO(3)(LMO)/STO interface. Using the technique of X-ray resonant
magnetic scattering (XRMS), we can probe the interfaces of complicated layered
structures and quantitatively model depth-dependent magnetic profiles as a
function of distance from the interface. Comparisons of the average electronic
and magnetic properties at the interface are made independently using X-ray
absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The
XAS and the XMCD demonstrate that the electronic and magnetic structure of the
LMO layer at the modified interface is qualitatively equivalent to the
underlying LSMO film. From the temperature dependence of the XMCD, it is found
that the near surface magnetization for both interfaces falls off faster than
the bulk. For all temperatures in the range of 50K - 300K, the magnetic
profiles for both systems always show a ferromagnetic component at the
interface with a significantly suppressed magnetization that evolves to the
bulk value over a length scale of ~1.6 - 2.4 nm. The LSMO/LMO/STO interface
shows a larger ferromagnetic (FM) moment than the LSMO/STO interface, however
the difference is only substantial at low temperature.Comment: 4 pages, 4 figure
Numerical residual perturbation solution applied to an earth satellite including luni-solar effects
Mathematical model and computer program for numerical solution of earth orbit differential equations of motio
Low Temperature AC Conductivity in BSCCO (2212)
We report measurements of anamolously large dissipative conductivities in
BiSrCaCuO(2212) at low temperatures. We have measured the complex conductivity
of BSCCO thin films at 100-600 GHz as a function of doping from the underdoped
to the overdoped state. At low temperatures there exists a residual dissipative
conductivity which scales with the T=0 superfluid density as the doping is
varied. This residual dissipative conductivity is larger than the possible
contribution from a thermal population of quasiparticles at the d-wave gap
nodes.Comment: Submitted to the Proceedings of the 22nd International Low
Temperature Physics Conference. To be published in Physica B
(http://www.elsevier.nl/locate/physb); 2 Pages with 2 Figure
Empircial labor search models: A survey
This paper surveys the existing empirical research that uses search theory to empirically analyze labor supply questions in a structural framework, using data on individual labor market transitions and durations, wages, and individual characteristics. The starting points of the literature are the Mincerian earnings function, Heckman’s classic selection model, and dynamic optimization theory. We develop a general framework for the labor market where the search for a job involves dynamic decision making under uncertainity. It can be specialized to be in agreement with most published research using labor search models. We discuss estimation, policy evaluation with the estimated model, equilibrium model versions, and the decomposition of wage variation into factors due to heterogeneity of various model determinants as well as search frictions themselves. We summarize the main empirical conclusions.Labor search models;
Satellite motion for all inclinations around an oblate planet
Satellite motion for all inclinations around oblate plane
Pure single photon generation by type-I PDC with backward-wave amplification
We explore a promising method of generating pure heralded single photons. Our
approach is based on parametric downconversion in a periodically-poled
waveguide. However, unlike conventional downconversion sources, the photon
pairs are counter-propagating: one travels with the pump beam in the forward
direction while the other is backpropagating towards the laser source. Our
calculations reveal that these downconverted two-photon states carry minimal
spectral correlations within each photon-pair. This approach offers the
possibility to employ a new range of downconversion processes and materials
like PPLN (previously considered unsuitable due to their unfavorable
phasematching properties) to herald pure single photons over a broad frequency
range.Comment: 8 pages, 3 figures, minor text changes and reformattin
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