67 research outputs found
Transport Properties of d-Wave Superconductors in the Vortex State
We calculate the magnetic field dependence of quasiparticle transport
properties in the vortex state of a d-wave superconductor arising solely from
the quasiparticle's Doppler shift in the superflow field surrounding the
vortex. Qualitative features agree well with experiments on cuprate and heavy
fermion superconductors at low fields and temperatures. We derive scaling
relations in the variable valid at sufficiently low temperatures
and fields , but show that these relations depend on the scattering
phase shift, and are in general fulfilled only approximately even in the clean
limit, due to the energy dependence of the quasiparticle relaxation time.Comment: 5 pages, 2 Postscript figure
Temperature dependence of the Kondo resonance and its satellites in CeCu_2Si_2
We present high-resolution photoemission spectroscopy studies on the Kondo
resonance of the strongly-correlated Ce system CeCuSi. Exploiting the
thermal broadening of the Fermi edge we analyze position, spectral weight, and
temperature dependence of the low-energy 4f spectral features, whose major
weight lies above the Fermi level . We also present theoretical
predictions based on the single-impurity Anderson model using an extended
non-crossing approximation (NCA), including all spin-orbit and crystal field
splittings of the 4f states. The excellent agreement between theory and
experiment provides strong evidence that the spectral properties of
CeCuSi can be described by single-impurity Kondo physics down to K.Comment: 4 pages, 3 figure
Thermodynamic and Transport Properties of CeMg2Cu9 under Pressure
We report the transport and thermodynamic properties under hydrostatic
pressure in the antiferromagnetic Kondo compound CeMg2Cu9 with a
two-dimensional arrangement of Ce atoms. Magnetic specific heat Cmag(T) shows a
Schottky-type anomaly around 30 K originating from the crystal electric field
(CEF) splitting of the 4f state with the first excited level at \Delta_{1}/kB =
58 K and the second excited level at \Delta_{2}/kB = 136 K from the ground
state.
Electric resistivity shows a two-peaks structure due to the Kondo effect on
each CEF level around T_{1}^{max} = 3 K and T_{2}^{max} = 40 K. These peaks
merge around 1.9 GPa with compression. With increasing pressure, Neel
temperature TN initially increases and then change to decrease. TN finally
disappears at the quantum critical point Pc = 2.4 GPa.Comment: 10 pages, 6 figure
Specific heat of Ce_{0.8}La_{0.2}Al_{3} in magnetic fields: a test of the anisotropic Kondo picture
The specific heat C of Ce_{0.8}La_{0.2}Al_{3} has been measured as a function
of temperature T in magnetic fields up to 14 T. A large peak in C at 2.3 K has
recently been ascribed to an anisotropic Kondo effect in this compound. A 14-T
field depresses the temperature of the peak by only 0.2 K, but strongly reduces
its height. The corresponding peak in C/T shifts from 2.1 K at zero field to
1.7 K at 14 T. The extrapolated specific heat coefficient C/T(T->0) increases
with field over the range studied. We show that these trends are inconsistent
with the anisotropic Kondo model.Comment: 4 pages, 5 figures, ReVTeX + eps
Genetic selection for fast growth generates bone architecture characterised by enhanced periosteal expansion and limited consolidation of the cortices but a diminution in the early responses to mechanical loading.
International audienceBone strength is, in part, dependent on a mechanical input that regulates the (re)modelling of skeletal elements to an appropriate size and architecture to resist fracture during habitual use. The rate of longitudinal bone growth in juveniles can also affect fracture incidence in adulthood, suggesting an influence of growth rate on later bone quality. We have compared the effects of fast and slow growth on bone strength and architecture in the tibiotarsi of embryonic and juvenile birds. The loading-related biochemical responses (intracellular G6PD activity and NO release) to mechanical load were also determined. Further, we have analysed the proliferation and differentiation characteristics of primary tibiotarsal osteoblasts from fast and slow-growing strains. We found that bones from chicks with divergent growth rates display equal resistance to applied loads, but weight-correction revealed that the bones from juvenile fast growth birds are weaker, with reduced stiffness and lower resistance to fracture. Primary osteoblasts from slow-growing juvenile birds proliferated more rapidly and had lower alkaline phosphatase activity. Bones from fast-growing embryonic chicks display rapid radial expansion and incomplete osteonal infilling but, importantly, lack mechanical responsiveness. These findings are further evidence that the ability to respond to mechanical inputs is crucial to adapt skeletal architecture to generate a functionally appropriate bone structure and that fast embryonic and juvenile growth rates may predispose bone to particular architectures with increased fragility in the adult. (C) 2009 Elsevier Inc. All rights reserved
The Kondo Resonance in Electron Spectroscopy
The Kondo resonance is the spectral manifestation of the Kondo properties of
the impurity Anderson model, and also plays a central role in the dynamical
mean-field theory (DMFT) for correlated electron lattice systems. This article
presents an overview of electron spectroscopy studies of the resonance for the
4f electrons of cerium compounds, and for the 3d electrons of V_2O_3, including
beginning efforts at using angle resolved photoemission to determine the
k-dependence of the resonance. The overview includes the comparison and
analysis of spectroscopy data with theoretical spectra as calculated for the
impurity model and as obtained by DMFT, and the Kondo volume collapse
calculation of the cerium alpha-gamma phase transition boundary, with its
spectroscopic underpinnings.Comment: 32 pages, 11 figures, 151 references; paper for special issue of J.
Phys. Soc. Jpn. on "Kondo Effect--40 Years after the Discovery
A Superconducting Instability in the Infinite-U Anderson Lattice in the Presence of Crystal Electric Fields
We report evidence of a superconducting instability (of symmetry) in
the infinite-U Anderson lattice in the presence of crystal fields of cubic
symmetry. We assume a lattice of sites, each with a total angular momentum
of that is split by crystal fields into a low-lying doublet of
symmetry and an excited quartet of symmetry. Slave Bosons
on the sites create and destroy configurations and Lagrange
multipliers at each site enforce the occupancy constraint due to the
infinite Coulomb repulsion. Quasiparticle interactions are due to exchange of
density fluctuations, which are represented by fluctuations in the slave
Bosons and Lagrange multipliers. We use the so-called analytic tetrahedron
method to calculate the dressed (to order 1/N) Boson Green functions. In weak
couping, the exchange of the dressed Bosons gives rise to a superconducting
instability of , , symmetry. The , ``s-wave'',
channel has strongly repulsive interactions and hence no pairing instability.
The channel exhibits weakly repulsive interactions. Average
quasiparticle interactions in the , , , channel
fluctuate strongly as a function of the number of tetrahedra used to calculate
the Bosonic Green functions,Comment: 66 pages+ 17 postscript figures, LATE
- …