655 research outputs found
Gilbert Damping in Conducting Ferromagnets II: Model Tests of the Torque-Correlation Formula
We report on a study of Gilbert damping due to particle-hole pair excitations
in conducting ferromagnets. We focus on a toy two-band model and on a four-band
spherical model which provides an approximate description of ferromagnetic
(Ga,Mn)As. These models are sufficiently simple that disorder-ladder-sum vertex
corrections to the long-wavelength spin-spin response function can be summed to
all orders. An important objective of this study is to assess the reliability
of practical approximate expressions which can be combined with electronic
structure calculations to estimate Gilbert damping in more complex systems.Comment: 10 pages, 10 figures. Submitted to Phys. Rev.
Transport, magnetic, and structural properties of LaCeMnO thin films. Evidence for hole-doping
Cerium-doped manganite thin films were grown epitaxially by pulsed laser
deposition at C and oxygen pressure Pa and were
subjected to different annealing steps. According to x-ray diffraction (XRD)
data, the formation of CeO as a secondary phase could be avoided for
Pa. However, transmission electron microscopy shows the presence
of CeO nanoclusters, even in those films which appear to be single phase in
XRD. With O annealing, the metal-to-insulator transition temperature
increases, while the saturation magnetization decreases and stays well below
the theoretical value for electron-doped LaCeMnO with mixed
Mn/Mn valences. The same trend is observed with decreasing film
thickness from 100 to 20 nm, indicating a higher oxygen content for thinner
films. Hall measurements on a film which shows a metal-to-insulator transition
clearly reveal holes as dominating charge carriers. Combining data from x-ray
photoemission spectroscopy, for determination of the oxygen content, and x-ray
absorption spectroscopy (XAS), for determination of the hole concentration and
cation valences, we find that with increasing oxygen content the hole
concentration increases and Mn valences are shifted from 2+ to 4+. The
dominating Mn valences in the films are Mn and Mn, and only a
small amount of Mn ions can be observed by XAS. Mn and Ce
XAS signals obtained in surface-sensitive total electron yield mode are
strongly reduced in the bulk-sensitive fluorescence mode, which indicates
hole-doping in the bulk for those films which do show a metal-to-insulator
transition.Comment: 8 pages, 10 figure
The Complex Langevin method: When can it be trusted?
We analyze to what extent the complex Langevin method, which is in principle
capable of solving the so-called sign problems, can be considered as reliable.
We give a formal derivation of the correctness and then point out various
mathematical loopholes. The detailed study of some simple examples leads to
practical suggestions about the application of the method.Comment: 14 pages, including several eps figures and tables; clarification and
minor corrections added, to appear in PR
Triple valve infective endocarditis - a late diagnosis
Behcet\u27s disease is a systemic vasculitis of unknown aetiology with cardiac involvement as well as damage to other organs. Whether the sterile valvular inflammation which occurs in this autoimmune disease predisposes to bacterial adhesion and infective endocarditis is not yet established.
We present the case of a patient with Behcet disease in which transthoracic echocardiography showed mobile masses on the aortic, tricuspid, and mitral valves, leading to multivalvular infective endocarditis diagnosis, possibly in the context of valvular inflammation.
The case presented in this article confirms observation of other studies, namely that ultrasonography plays an important role in the diagnosis and evaluation of rheumatic diseases and permits optimal management in daily practice
LITHIUM SALTS OF FLUORINATED BORATE ESTERS FOR LITHIUM-ION BATTERIES
Lithium salts with fluorinated chelated orthoborate anions are prepared and used as electrolytes or electrolyte additives in lithium-ion batteries. The lithium salts have two chelate rings formed by the coordination of two bidentate ligands to a single boron atom. In addition, each chelate ring has two oxygen atoms bonded to one boron atom, methylene groups bonded to the two oxygen atoms, and one or more fluorinated carbon atoms bonded to and forming a cyclic bridge between the methylene groups
Interplay between Symmetric Exchange Anisotropy, Uniform Dzyaloshinskii-Moriya Interaction and Magnetic Fields in the Phase Diagram of Quantum Magnets and Superconductors
We theoretically study the joint influence of uniform Dzyaloshinskii-Moriya
(DM) interactions, symmetric exchange anisotropy (with its axis parallel to the
DM vector) and arbitrarily oriented magnetic fields on one-dimensional spin 1/2
antiferromagnets. We show that the zero-temperature phase diagram contains
three competing phases: (i) an antiferromagnet with Neel vector in the plane
spanned by the DM vector and the magnetic field, (ii) a {\em dimerized}
antiferromagnet with Neel vector perpendicular to both the DM vector and the
magnetic field, and (iii) a gapless Luttinger liquid. Phase (i) is destroyed by
a small magnetic field component along the DM vector and is furthermore
unstable beyond a critical value of easy-plane anisotropy, which we estimate
using Abelian and non-Abelian bosonization along with perturbative
renormalization group. We propose a mathematical equivalent of the spin model
in a one-dimensional Josephson junction (JJ) array located in proximity to a
bulk superconductor.
We discuss the analogues of the magnetic phases in the superconducting
context and comment on their experimental viability.Comment: 20 pages, 16 figures; submitted to Phys. Rev.
Generating random density matrices
We study various methods to generate ensembles of random density matrices of
a fixed size N, obtained by partial trace of pure states on composite systems.
Structured ensembles of random pure states, invariant with respect to local
unitary transformations are introduced. To analyze statistical properties of
quantum entanglement in bi-partite systems we analyze the distribution of
Schmidt coefficients of random pure states. Such a distribution is derived in
the case of a superposition of k random maximally entangled states. For another
ensemble, obtained by performing selective measurements in a maximally
entangled basis on a multi--partite system, we show that this distribution is
given by the Fuss-Catalan law and find the average entanglement entropy. A more
general class of structured ensembles proposed, containing also the case of
Bures, forms an extension of the standard ensemble of structureless random pure
states, described asymptotically, as N \to \infty, by the Marchenko-Pastur
distribution.Comment: 13 pages in latex with 8 figures include
The Hopf modules category and the Hopf equation
We study the Hopf equation which is equivalent to the pentagonal equation,
from operator algebras. A FRT type theorem is given and new types of quantum
groups are constructed. The key role is played now by the classical Hopf
modules category. As an application, a five dimensional noncommutative
noncocommutative bialgebra is given.Comment: 30 pages, Letax2e, Comm. Algebra in pres
Possible in vivo mechanisms involved in photodynamic therapy using tetrapyrrolic macrocycles
- …