419 research outputs found
Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems
Muon spin rotation and relaxation (SR) experiments have yielded evidence
that structural disorder is an important factor in many f-electron-based
non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour
are suggested by the observed broad and strongly temperature-dependent SR
(and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven
theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not
capable of describing the time-field scaling seen in muon spin relaxation
experiments, which suggest cooperative and critical spin fluctuations rather
than a distribution of local fluctuation rates. A strong empirical correlation
is established between electronic disorder and slow spin fluctuations in NFL
materialsComment: 24 pages, 15 figures, submitted to J. Phys.: Condens. Matte
Microscopic evidence for field-induced magnetism in CeCoIn
We present NMR data in the normal and superconducting states of CeCoIn
for fields close to T in the plane. Recent
experiments identified a first-order transition from the normal to
superconducting state for T, and a new thermodynamic phase below 290
mK within the superconducting state. We find that the Knight shifts of the
In(1), In(2) and the Co are discontinuous across the first-order transition and
the magnetic linewidths increase dramatically. The broadening differs for the
three sites, unlike the expectation for an Abrikosov vortex lattice, and
suggests the presence of static spin moments in the vortex cores. In the
low-temperature and high-field phase the broad NMR lineshapes suggest ordered
local moments, rather than a long wavelength quasiparticle spin density
modulation expected for an FFLO phase.Comment: 4 pages, 4 figures. to appear in Phys. Rev. Let
Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOsSb
Transverse-field muon spin rotation (SR) experiments in the
heavy-fermion superconductor PrOsSb ( K) suggest that
the superconducting penetration depth is temperature-independent
at low temperatures, consistent with a gapped quasiparticle excitation
spectrum. In contrast, radiofrequency (rf) inductive measurements yield a
stronger temperature dependence of , indicative of point nodes in
the gap. This discrepancy appears to be related to the multiband structure of
PrOsSb. Muon Knight shift measurements in PrOsSb
suggest that the perturbing effect of the muon charge on the neighboring
Pr crystalline electric field is negligibly small, and therefore is
unlikely to cause the difference between the SR and rf results.Comment: 10 pages, 7 figure
Knight Shift Anomalies in Heavy Electron Materials
We calculate non-linear Knight Shift vs. susceptibility anomalies
for Ce ions possessing local moments in metals. The ions are modeled with the
Anderson Hamiltonian and studied within the non-crossing approximation (NCA).
The non-linearity diminishes with decreasing Kondo temperature
and nuclear spin- local moment separation. Treating the Ce ions as an
incoherent array in CeSn, we find excellent agreement with the observed Sn
data.Comment: 4 pages, Revtex, 3 figures available upon request from
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Magneto-Transport Properties of Doped RuSrGdCuO
RuSrGdCuO, in which magnetic order and superconductivity coexist
with , is a complex material which poses new and
important questions to our understanding of the interplay between magnetic and
superconducting (SC) order. Resistivity, Hall effect and thermopower
measurements on sintered ceramic RuSrGdCuO are presented, together
with results on a broad range of substituted analogues. The Hall effect and
thermopower both show anomalous decreases below which may be
explained within a simple two-band model by a transition from localized to more
itinerant behavior in the RuO layer at .Comment: 10 pages, 7 figures, submitted to Phys. Rev. B., correspondence to
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Spin dynamics and ordering of a cuprate stripe-antiferromagnet
In La1.48Nd0.4Sr0.12CuO4 the 139La and 63Cu NQR relaxation rates and signal
wipe-out upon lowering temperature are shown to be due to purely magnetic
fluctuations. They follow the same renormalized classical behavior as seen in
neutron data, when the electronic spins order in stripes, with a small spread
in spin stiffness (15% spread in activation energy). The La signal, which
reappears at low temperatures, is magnetically broadened and experiences
additional wipe-out due to slowing down of the Nd fluctuations.Comment: 4 pages including 3 figures - ref. 16 adde
Mesoscopic phase separation in La2CuO4.02 - a 139La NQR study
In crystals of La2CuO4.02 oxygen diffusion can be limited to such small
length scales, that the resulting phase separation is invisible for neutrons.
Decomposition of the 139La NQR spectra shows the existence of three different
regions, of which one orders antiferromagnetically below 17K concomitantly with
the onset of a weak superconductivity in the crystal. These regions are
compared to the macroscopic phases seen previously in the title compound and
the cluster-glass and striped phases reported for the underdoped Sr-doped
cuprates.Comment: 4 pages, RevTeX, 5 figures, to be published in PR
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