16,746 research outputs found
Electronic phase separation due to magnetic polaron formation in the semimetallic ferromagnet EuB - A weakly-nonlinear-transport study
We report measurements of weakly nonlinear electronic transport, as measured
by third-harmonic voltage generation , in the low-carrier density
semimetallic ferromagnet EuB, which exhibits an unusual magnetic ordering
with two consecutive transitions at \,K and \,K. Upon cooling in zero magnetic field through the ferromagnetic
transition, the dramatic drop in the linear resistivity at the upper transition
coincides with the onset of nonlinearity, and upon further cooling is
followed by a pronounced peak in at the lower transition
. Likewise, in the paramagnetic regime, a drop of the material's
magnetoresistance precedes a magnetic-field-induced peak in nonlinear
transport. A striking observation is a linear temperature dependence of
. We suggest a picture where at the upper transition
the coalescing MP form a conducting path giving rise to a strong
decrease in the resistance. The MP formation sets in at around \,K below which these entities are isolated and strongly fluctuating, while
growing in number. The MP then start to form links at , where
percolative electronic transport is observed. The MP merge and start forming a
continuum at the threshold . In the paramagnetic temperature regime
, MP percolation is induced by a magnetic field, and the
threshold accompanied by charge carrier delocalization occurs at a single
critical magnetization.Comment: to appear in J. Kor. Phys. Soc (ICM2012 conference contribution
Coherent hard x-rays from attosecond pulse train-assisted harmonic generation
High-order harmonic generation from atomic systems is considered in the
crossed fields of a relativistically strong infrared laser and a weak
attosecond-pulse train of soft x-rays. Due to one-photon ionization by the
x-ray pulse, the ionized electron obtains a starting momentum that compensates
the relativistic drift which is induced by the laser magnetic field, and allows
the electron to efficiently emit harmonic radiation upon recombination with the
atomic core in the relativistic regime. In this way, short pulses of coherent
hard x-rays of up to 40 keV energy and 10 as duration can be brought about
Field-induced commensurate long-range order in the Haldane-gap system NDMAZ
High-field neutron diffraction studies of the new quantum-disordered S=1
linear-chain antiferromagnet Ni(CHN)N(ClO) (NDMAZ)
are reported. At T=70 mK, at a critical field T applied along the
(013) direction, a phase transition to a commensurate N\'{e}el-like ordered
state is observed. The results are discussed in the context of existing
theories of quantum phase transitions in Haldane-gap antiferromagnets, and in
comparions with previous studies of the related system
Ni(CHN)N(PF)
Microscopic laser-driven high-energy colliders
The concept of a laser-guided collider in the high-energy regime is
presented and its feasibility discussed. Ultra-intense laser pulses and strong
static magnetic fields are employed to unite in one stage the electron and
positron acceleration and their head-on-head collision. We show that the
resulting coherent collisions in the GeV regime yield an enormous enhancement
of the luminosity with regard to conventional incoherent colliders
PACS photometer calibration block analysis
The absolute stability of the PACS bolometer response over the entire mission
lifetime without applying any corrections is about 0.5% (standard deviation) or
about 8% peak-to-peak. This fantastic stability allows us to calibrate all
scientific measurements by a fixed and time-independent response file, without
using any information from the PACS internal calibration sources. However, the
analysis of calibration block observations revealed clear correlations of the
internal source signals with the evaporator temperature and a signal drift
during the first half hour after the cooler recycling. These effects are small,
but can be seen in repeated measurements of standard stars. From our analysis
we established corrections for both effects which push the stability of the
PACS bolometer response to about 0.2% (stdev) or 2% in the blue, 3% in the
green and 5% in the red channel (peak-to-peak). After both corrections we still
see a correlation of the signals with PACS FPU temperatures, possibly caused by
parasitic heat influences via the Kevlar wires which connect the bolometers
with the PACS Focal Plane Unit. No aging effect or degradation of the
photometric system during the mission lifetime has been found.Comment: 15 pages, accepted for publication in Experimental Astronom
Unifying Amplitude and Phase Analysis: A Compositional Data Approach to Functional Multivariate Mixed-Effects Modeling of Mandarin Chinese
Mandarin Chinese is characterized by being a tonal language; the pitch (or
) of its utterances carries considerable linguistic information. However,
speech samples from different individuals are subject to changes in amplitude
and phase which must be accounted for in any analysis which attempts to provide
a linguistically meaningful description of the language. A joint model for
amplitude, phase and duration is presented which combines elements from
Functional Data Analysis, Compositional Data Analysis and Linear Mixed Effects
Models. By decomposing functions via a functional principal component analysis,
and connecting registration functions to compositional data analysis, a joint
multivariate mixed effect model can be formulated which gives insights into the
relationship between the different modes of variation as well as their
dependence on linguistic and non-linguistic covariates. The model is applied to
the COSPRO-1 data set, a comprehensive database of spoken Taiwanese Mandarin,
containing approximately 50 thousand phonetically diverse sample contours
(syllables), and reveals that phonetic information is jointly carried by both
amplitude and phase variation.Comment: 49 pages, 13 figures, small changes to discussio
A waveguide atom beamsplitter for laser-cooled neutral atoms
A laser-cooled neutral-atom beam from a low-velocity intense source is split
into two beams while guided by a magnetic-field potential. We generate our
multimode-beamsplitter potential with two current-carrying wires on a glass
substrate combined with an external transverse bias field. The atoms bend
around several curves over a -cm distance. A maximum integrated flux of
is achieved with a current density of
in the 100- diameter
wires. The initial beam can be split into two beams with a 50/50 splitting
ratio
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