337 research outputs found
Magnetization reversal and nonexponential relaxation via instabilities of internal spin waves in nanomagnets
A magnetic particle with atomic spins ordered in an unstable direction is an
example of a false vacuum that decays via excitation of internal spin waves.
Coupled evolution of the particle's magnetization (or the vacuum state) and
spin waves, considered in the time-dependent vacuum frame, leads to a peculiar
relaxation that is very fast at the beginning but slows down to a
nonexponential long tail at the end. The two main scenarios are linear and
exponential spin-wave instabilities. For the former, the longitudinal and
transverse relaxation rates have been obtained analytically. Numerical
simulations show that the particle's magnetization strongly decreases in the
middle of reversal and then recovers.Comment: 6 EPL pages, 4 figure
Analysis of the Kondo effect in ferromagnetic atomic-sized contacts
Atomic contacts made of ferromagnetic metals present zero-bias anomalies in
the differential conductance due to the Kondo effect. These systems provide a
unique opportunity to perform a statistical analysis of the Kondo parameters in
nanostructures since a large number of contacts can be easily fabricated using
break-junction techniques. The details of the atomic structure differ from one
contact to another so a large number of different configurations can be
statistically analyzed. Here we present such a statistical analysis of the
Kondo effect in atomic contacts made from the ferromagnetic transition metals
Ni, Co and Fe. Our analysis shows clear differences between materials that can
be understood by fundamental theoretical considerations. This combination of
experiments and theory allow us to extract information about the origin and
nature of the Kondo effect in these systems and to explore the influence of
geometry and valence in the Kondo screening of atomic-sized nanostructures.Comment: 17 pages, 11 figure
Louisville / Jefferson County Hazardous Material Commodity Flow Analysis
This report presents the results of a Hazardous Material Commodity Flow Analysis for the Louisville Metro area and Jefferson County. Study components were conducted by Western Kentucky University in partnership with Louisville / Jefferson County Emergency Management Agency. The study area was focused in Louisville and Jefferson County, Louisville Metro area, and included monitoring in Bullet County and Oldham County, as shown in Figure 1.1. As part of the study, hazardous material transport was monitored at the following sites: Interstate-64 (I-64), East and West bound lanes at The Belvedere; I-64, East and West bound lanes at Blankenbaker exit location; Interstate-65 (I-65, North and South bound lanes at the Jewish Hospital; I-65, North and South bound lanes at Brooks, KY exit location; Interstate-71 (I-71), North and South bound lanes at Oldham County rest areas; Hwy 841, North and South bound Lanes at Westport Road. The purpose of this report is to present information on patterns of hazardous material commodity flow along I-64, I-65, I-71 and Highway 841, as observed from June 11, 2012 to August 2, 2012. This report also summarizes incidents involving hazardous materials over the previous 3 years, August 2008 to June 2011, in the Louisville Metro area. Finally, this report assesses survey information collected from fixed facilities that ship and receive hazardous materials in the Louisville Metro Area
PSPACE-completeness of Pulling Blocks to Reach a Goal
We prove PSPACE-completeness of all but one problem in a large space of
pulling-block problems where the goal is for the agent to reach a target
destination. The problems are parameterized by whether pulling is optional, the
number of blocks which can be pulled simultaneously, whether there are fixed
blocks or thin walls, and whether there is gravity. We show NP-hardness for the
remaining problem, Pull?-1FG (optional pulling, strength 1, fixed blocks, with
gravity).Comment: Full version of JCDCGGG2019 paper, 22 pages, 25 figure
Low Energy Properties of the (n,n) Carbon Nanotubes
According to band theory, an ideal undoped (n,n) carbon nanotube is metallic.
We show that the electron-electron interaction causes it to become Mott
insulating with a spin gap. More interestingly, upon doping it develops
superconducting fluctuations.Comment: 5pages, 2eps figures, one reference added, final version, accepted to
PR
On the theory of superconductivity in ferromagnetic superconductors with triplet pairing
We point out that ferromagnetic superconductors with triplet pairing and
strong spin-orbit coupling are even in the simplest case at least two-band
superconductors. The Gor'kov type formalism for such superconductors is
developed and the Ginzburg-Landau equations are derived. The dependence of the
critical temperature on the concentration of ordinary point-like impurities is
found. Its nonuniversality could serve as a qualitative measure of the two-band
character of ferromagnetic superconductors. The problem of the upper critical
field determination is also discussed.Comment: 8 pages, no figure; important changes with respect to the previous
versions due to the correction of a mistake: in this new version, a more
general form is considered for the order parameter (the two-components of the
order parameter were considered before as equal, which is in general not
true) ; submitted to Physical Review
Direct Hopf Bifurcation in Parametric Resonance of Hybridized Waves
We study parametric resonance of interacting waves having the same wave
vector and frequency. In addition to the well-known period-doubling instability
we show that under certain conditions the instability is caused by a Hopf
bifurcation leading to quasiperiodic traveling waves. It occurs, for example,
if the group velocities of both waves have different signs and the damping is
weak. The dynamics above the threshold is briefly discussed. Examples
concerning ferromagnetic spin waves and surface waves of ferro fluids are
discussed.Comment: Appears in Phys. Rev. Lett., RevTeX file and three postscript
figures. Packaged using the 'uufiles' utility, 33 k
Microscopic theory for quantum mirages in quantum corrals
Scanning tunneling microscopy permits to image the Kondo resonance of a
single magnetic atom adsorbed on a metallic surface. When the magnetic impurity
is placed at the focus of an elliptical quantum corral, a Kondo resonance has
been recently observed both on top of the impurity and on top of the focus
where no magnetic impurity is present. This projection of the Kondo resonance
to a remote point on the surface is referred to as quantum mirage. We present a
quantum mechanical theory for the quantum mirage inside an ideal quantum corral
and predict that the mirage will occur in corrals with shapes other than
elliptical
Grain Boundary Induced Magneto-Far Infrared Resonances in Superconducting YBaCuO Thin Films
Spectral features induced by 45 in-plane misoriented grains have
been observed in the far infrared magneto-transmission of YBaCuO thin films. Two strong dispersive features are found at 80 and
160 and a weaker one at 116 . The data can be well
represented by Lorentzian oscillator contributions to the conductivity. Several
possible interpretations are discussed. We conclude that the resonances are due
to vortex core excitations.Comment: Latex file (14 pages) + 4 Postscript figures, uuencode
- …