1,592 research outputs found
Interplay of strongly correlated electrons and localized Ising moments in one-dimension
We study the ground state properties of the one-dimensional quarter-filled
strongly correlated electronic chain coupled by to another chain of
antiferromagnetic Ising moments. We focus on the case where the large Coulomb
interactions localize the charges on every other site. Both the electronic
spins and the Ising moments interact antiferromagnetically within each chain by
and , respectively. Since the number of electrons is half as
that of the Ising moments the period of magnetic correlation of these two
chains are incommensurate. In the presence of , the frustration of and arises, which may lead the system to the intriguing
magneto-electric effect.Comment: 8pages 6figure
Taking advantage of multiplet structure for lineshape analysis in Fourier space
Lineshape analysis is a recurrent and often computationally intensive task in
optics, even more so for multiple peaks in the presence of noise. We
demonstrate an algorithm which takes advantage of peak multiplicity (N) to
retrieve line shape information. The method is exemplified via analysis of
Lorentzian and Gaussian contributions to individual lineshapes for a practical
spectroscopic measurement and benefits from a linear increase in sensitivity
with the number N. The robustness of the method and its benefits in terms of
noise reduction and order of magnitude improvement in run-time performance are
discussed.Comment: 12 pages, 6 figure
The importance of thermal disorder and electronic occupation for the T-dependence of the optical conductivity in FeSi and MnSi
The spectral weight (SW) for optical transitions in FeSi and MnSi are
calculated as function of temperature by means of LMTO-LDA band calculations.
The main effects, caused by structural disorder and electronic Fermi-Dirac
distribution, act oppositely on the T-dependence of the SW, while the variation
of the magnetic moment in MnSi has only a minor effect. The calculations agree
with the experimental findings of an increasing SW in FeSi and a decreasing SW
in MnSi as function of T. The results can be understood from the change of the
bandstructure with disorder.Comment: (5 pages, 4 figures
Thermoelectric properties of junctions between metal and strongly correlated semiconductor
We propose a junction of metal and rare-earth compound semiconductor as the
basis for a possible efficient low-temperature thermoelectric device. If an
overlayer of rare earth atoms differing from the bulk is placed at the
interface, very high values of the figure of merit ZT can be reached at low
temperature. This is due to sharp variation of the transmission coefficient of
carriers across the junction at a narrow energy range, which is intrinsically
linked to the localized character of the overlayer f-orbital.Comment: RevTeX 3.0, 4 pages, 3 postscript figures. To be published in Applied
Physics Letter
Switchable Hardening of a Ferromagnet at Fixed Temperature
The intended use of a magnetic material, from information storage to power
conversion, depends crucially on its domain structure, traditionally crafted
during materials synthesis. By contrast, we show that an external magnetic
field applied transverse to the preferred magnetization of a model disordered
uniaxial ferromagnet is an isothermal regulator of domain pinning. At elevated
temperatures, near the transition into the paramagnet, modest transverse fields
increase the pinning, stabilize the domain structure, and harden the magnet,
until a point where the field induces quantum tunneling of the domain walls and
softens the magnet. At low temperatures, tunneling completely dominates the
domain dynamics and provides an interpretation of the quantum phase transition
in highly disordered magnets as a localization/delocalization transition for
domain walls. While the energy scales of the rare earth ferromagnet studied
here restrict the effects to cryogenic temperatures, the principles discovered
are general and should be applicable to existing classes of highly anisotropic
ferromagnets with ordering at room temperature or above.Comment: 10 pages, 4 figure
\order(\Gamma) Corrections to pair production in and collisions
Several schemes to introduce finite width effects to reactions involving
unstable elementary particles are given and the differences between them are
investigated. The effects of the different schemes is investigated numerically
for pair production. In we find that the effect of the
non-resonant graphs cannot be neglected for \sqrt{s}\geq400\GeV. There is no
difference between the various schemes to add these to the resonant graphs away
from threshold, although some violate gauge invariance. On the other hand, in
the reaction the effect of the non-resonant graphs is
large everywhere, due to the -channel pole. However, even requiring that the
outgoing lepton is observable () reduces the
contribution to about 1\%. Again, the scheme dependence is negligible here.Comment: 9 pages plus 6 with figures (.uu at end, also available with
anonymous ftp from pss058.psi.ch [129.129.40.58]), LaTeX, LMU-21/92,
PSI-PR-93-05, TTP92-3
Temperature and Field Dependence of Magnetic Domains in LaSrMnO
Colossal magnetoresistance and field-induced ferromagnetism are well
documented in manganite compounds. Since domain wall resistance contributes to
magnetoresistance, data on the temperature and magnetic field dependence of the
ferromagnetic domain structure are required for a full understanding of the
magnetoresistive effect. Here we show, using cryogenic Magnetic Force
Microscopy, domain structures for the layered manganite
LaSrMnO as a function of temperature and magnetic
field. Domain walls are suppressed close to the Curie temperature T, and
appear either via the application of a c-axis magnetic field, or by decreasing
the temperature further. At temperatures well below T, new domain walls,
stable at zero field, can be formed by the application of a c-axis field.
Magnetic structures are seen also at temperatures above T: these features
are attributed to inclusions of additional Ruddleston-Popper manganite phases.
Low-temperature domain walls are nucleated by these ferromagnetic inclusions.Comment: 6 figure
Dynamical mean field theory of correlated gap formation in Pu monochalcogenides
The correlated Kondo insulator state of the plutonium monochalcogenides is
investigated using the dynamical mean field theory (DMFT) and the local density
approximation +U (LDA+U). The DMFT-dynamical fluctuations lead to a correlated
insulator state at elevated temperature, in sharp contrast to the static LDA+U
approach that fails to reproduce both the insulating behavior and anomalous
lattice constant. The DMFT conversely predicts the experimentally observed
anomalous increase of the gap with pressure and explains the lattice constant
very well.Comment: 4 pages, 4 figure
Direct and alignment-insensitive measurement of cantilever curvature
We analytically derive and experimentally demonstrate a method for the
simultaneous measurement of deflection for large arrays of cantilevers. The
Fresnel diffraction patterns of a cantilever independently reveals tilt,
curvature, cubic and higher order bending of the cantilever. It provides a
calibrated absolute measurement of the polynomial coefficients describing the
cantilever shape, without careful alignment and could be applied to several
cantilevers simultaneously with no added complexity. We show that the method is
easily implemented, works in both liquid mediums and in air, for a broad range
of displacements and is especially suited to the requirements for multi-marker
biosensors.Comment: 5 Pages, 4 figures, letter forma
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