137 research outputs found
Theoretische Untersuchung der reibungsbehafteten Stroemung in rotationssymmetrischen Duesen zur Auslegung eines Fluessigmetalltargets fuer eine Spallationsneutronenquelle
Low Temperature Anomaly in Mesoscopic Kondo Wires
We report the observation of an anomalous magnetoresistance in extremely
dilute quasi-one-dimensional AuFe wires at low temperatures, along with a
hysteretic background at low fields. The Kondo resistivity does not show the
unitarity limit down to the lowest temperature, implying uncompensated spin
states. We suggest that the anomalous magnetoresistance may be understood as
the interference correction from the accumulation of geometric phase in the
conduction electron wave function around the localized impurity spin.Comment: Four pages, five figure
Fluiddynamische Untersuchungen zur Auslegung eines Fluessigmetalltargets fuer eine Spallationsneutronenquelle
Strong coupling in the Kondo problem in the low-temperature region
The magnetic field dependence of the average spin of a localized electron
coupled to conduction electrons with an antiferromagnetic exchange interaction
is found for the ground state. In the magnetic field range
( is the Kondo temperature) there is an inflection point, and in the
strong magnetic field range , the correction to the average spin
is proportional to . In zero magnetic field, the interaction
with conduction electrons also leads to the splitting of doubly degenerate spin
impurity states
Kondo effect in a magnetic field and the magnetoresistivity of Kondo alloys
The effect of a magnetic field on the spectral density of a
Kondo impurity is investigated at zero and finite temperatures by using
Wilson's numerical renormalization group method. A splitting of the total
spectral density is found for fields larger than a critical value
, where is the Kondo scale. The splitting
correlates with a peak in the magnetoresistivity of dilute magnetic alloys
which we calculate and compare with the experiments on
. The linear magnetoconductance of quantum
dots exhibiting the Kondo effect is also calculated.Comment: 4 pages, 4 eps figure
Direct Evidence of the Role of Hybridization in the X-Ray Magnetic Circular Dichroism of a-Ce
We present an x-ray magnetic circular dichroism (XMCD) study of a [Ce(10 Ã…)/Fe(30 Ã…)] multilayer
performed at the Ce-M4,5 absorption edges. In this system the Ce-4f electrons are strongly hybridized
with the valence band. XMCD experiments show that they carry an ordered magnetic moment. The
differences of the shape of the XMCD signals of a typical g-like compound (CeCuSi) and of the Ce/
Fe multilayer highlight the role of hybridization in determining the ground state of cerium atoms in the
multilayer, which results in a mixing of J = 5/2 and J = 7/2 coupled states
Tuning the 4f-state occupancy of cerium in highly correlated CeSi/ Fe multilayers: a study by x-ray absorption spectroscopy
Spectra of x-ray absorption and magnetic circular dichroism were measured at
M4,5(3d) and L2,3(2p) edges of Ce in multilayers [Ce(1-x)Six/Fe]xn, with x
between 0.1 and 0.65. The study uncovers the highly correlated nature of this
layered system. An alpha-phase like electronic configuration of Ce is observed,
with ordered magnetic moments on the 4f and 5d electrons induced by the
interaction with Fe. Increasing the Si content reduces the strength of the
hy-bridization between the 4f and conduction-band states which is reflected in
a growing occupation and magnetic polarization of the 4f states. Variations of
the shape and intensity of the L2,3-edge dichroism spectra, discussed in a
simple phenomenological model, show the importance of the exchange interaction
between the Ce-4f and 5d electrons, spin polarized by the interaction with Fe
at the interfaces, for the electronic structure of Ce at high Si concentration
and low temperature. A model of the band structure of rare-earth
transition-metal compounds permits to argue that magnetic order on the Ce 4f
electrons in the multilayers is due to different mechanisms: to hybridization
of the Ce-4f with the Fe-3d states at low Si concentration and to intra-atomic
4f-5d exchange at high Si concentration. This is at variance with magnetic
order in the intermetallics CeSi2-delta and CeSi which results from interaction
between the localized 4f magnetic moments mediated by the Si-derived (s,p)
conduction electrons, in competition with the Kondo effect.Comment: 31 pages, 9 figures, submitted to Phys. Rev.
Possible robust insulator-superconductor transition on solid inert gas and other substrates
We present observations of the insulator-superconductor transition in
ultrathin films of Bi on amorphous quartz, quartz coated with Ge, and for the
first time, solid xenon condensed on quartz. The relative permeability
ranges from 1.5 for Xe to 15 for Ge. Though we find screening
effects as expected, the I-S transition is robust, and unmodified by the
substrate. The resistance separatrix is found to be close to h/4e^2 and the
crossover thickness close to for all substrates. I-V studies and
Aslamazov-Larkin analyses indicate superconductivity is inhomogeneous. The
transition can be understood in terms of a percolation model.Comment: accepted in Physical Review
Number and type of vertebral deformities: Epidemiological characteristics and relation to back pain and height loss
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