783 research outputs found
The Transition from Heavy Fermion to Mixed Valence in Ce1-xYxAl3: A Quantitative Comparison with the Anderson Impurity Model
We present a neutron scattering investigation of Ce1-xYxAl3 as a function of
chemical pressure, which induces a transition from heavy-fermion behavior in
CeAl3 (TK=5 K) to a mixed-valence state at x=0.5 (TK=150 K). The crossover can
be modeled accurately on an absolute intensity scale by an increase in the k-f
hybridization, Vkf, within the Anderson impurity model. Surprisingly, the
principal effect of the increasing Vkf is not to broaden the low-energy
components of the dynamic magnetic susceptibility but to transfer spectral
weight to high energy.Comment: 4 pages, 5 figure
Physical properties of noncentrosymmetric superconductor LaIrSi3: A {\mu}SR study
The results of heat capacity C_p(T, H) and electrical resistivity \rho(T,H)
measurements down to 0.35 K as well as muon spin relaxation and rotation
(\muSR) measurements on a noncentrosymmetric superconductor LaIrSi3 are
presented. Powder neutron diffraction confirmed the reported noncentrosymmetric
body-centered tetragonal BaNiSn3-type structure (space group I4\,mm) of
LaIrSi3. The bulk superconductivity is observed below T_c = 0.72(1) K. The
intrinsic \Delta C_e/\gamma_n T_c = 1.09(3) is significantly smaller than the
BCS value of 1.43, and this reduction is accounted by the \alpha-model of BCS
superconductivity. The analysis of the superconducting state C_e(T) data by the
single-band \alpha-model indicates a moderately anisotropic order parameter
with the s-wave gap \Delta(0)/k_B T_c = 1.54(2) which is lower than the BCS
value of 1.764. Our estimates of various normal and superconducting state
parameters indicate a weakly coupled electron-phonon driven type-I s-wave
superconductivity in LaIrSi3. The \muSR results also confirm the conventional
type-I superconductivity in LaIrSi3 with a preserved time reversal symmetry and
hence a singlet pairing superconducting ground state.Comment: 11 pages, 8 figures, 2 table
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR
Non-Fermi-liquid behavior in Ce(RuFe)Ge: cause and effect
We present inelastic neutron scattering measurements on the intermetallic
compounds Ce(RuFe)Ge (=0.65, 0.76 and 0.87). These
compounds represent samples in a magnetically ordered phase, at a quantum
critical point and in the heavy-fermion phase, respectively. We show that at
high temperatures the three compositions have the identical response of a local
moment system. However, at low temperatures the spin fluctuations in the
critical composition are given by non-Fermi-liquid dynamics, while the spin
fluctuations in the heavy fermion system show a simple exponential decay in
time. In both compositions, the lifetime of the fluctuations is determined
solely by the distance to the quantum critical point. We discuss the
implications of these observations regarding the possible origins of
non-Fermi-liquid behavior in this system.Comment: 4 figures, submitted to PR
Direct observation of non-local effects in a superconductor
We have used the technique of low energy muon spin rotation to measure the
local magnetic field profile B(z) beneath the surface of a lead film maintained
in the Meissner state (z depth from the surface, z <= 200 nm). The data
unambiguously show that B(z) clearly deviates from an exponential law and
represent the first direct, model independent proof for a non-local response in
a superconductor.Comment: 5 pages, 3 figure
Crystal-fields in YbInNi4 determined with magnetic form factor and inelastic neutron scattering
The magnetic form factor of YbInNi4 has been determined via the flipping
ratios R with polarized neutron diffraction and the scattering function S(Q,w)
was measured in an inelastic neutron scattering experiment. Both experiments
were performed with the aim to determine the crystal-field scheme. The magnetic
form factor clearly excludes the possibility of a \Gamma7 doublet as the ground
state. The inelastic neutron data exhibit two, almost equally strong peaks at
3.2 meV and 4.4 meV which points, in agreement with earlier neutron data,
towards a \Gamma8 quartet ground state. Further possibilities like a
quasi-quartet ground state are discussed.Comment: 7 pages, 5 figures, 2 tables, submitted to PR
Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity
We have measured the magnetic penetration depth of the recently discovered
binary superconductor MgB_2 using muon spin rotation and low field
-susceptibility. From the damping of the muon precession signal we find the
penetration depth at zero temperature is about 85nm. The low temperature
penetration depth shows a quadratic temperature dependence, indicating the
presence of nodes in the superconducting energy gap.Comment: 4 pages 3 figure
âEthnic groupâ, the state and the politics of representation
The assertion, even if only by implication, that âethnic groupâ categories represent ârealâ tangible entities, indeed identities, is commonplace not only in the realms of political and policy discourse but also amongst contemporary social scientists. This paper, following Brubaker (2002), questions this position in a number of key respects: of these three issues will dominate the discussion that follows.
First, there is an interrogation of the proposition that those to whom the categories/labels refer constitute sociologically meaningful âgroupsâ as distinct from (mere) human collectivities. Secondly, there is the question of how these categories emerge, i.e. exactly what series of events, negotiations and contestations lie behind their construction and social acceptance. Thirdly, and as a corollary to the latter point, we explore the process of reification that leads to these categories being seen to represent âreal things in the worldâ (ibid.)
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