2,681 research outputs found

### Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOs$_{4}$Sb$_{12}$

Transverse-field muon spin rotation ($\mu$SR) experiments in the
heavy-fermion superconductor PrOs$_{4}$Sb$_{12}$ ($T_{c}=1.85$ K) suggest that
the superconducting penetration depth $\lambda(T)$ 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 $\lambda(T)$, indicative of point nodes in
the gap. This discrepancy appears to be related to the multiband structure of
PrOs$_{4}$Sb$_{12}$. Muon Knight shift measurements in PrOs$_{4}$Sb$_{12}$
suggest that the perturbing effect of the muon charge on the neighboring
Pr$^{3+}$ crystalline electric field is negligibly small, and therefore is
unlikely to cause the difference between the $\mu$SR and rf results.Comment: 10 pages, 7 figure

### Euler characteristic of coherent sheaves on simplicial torics via the Stanley-Reisner ring

We combine work of Cox on the total coordinate ring of a toric variety and
results of Eisenbud-Mustata-Stillman and Mustata on cohomology of toric and
monomial ideals to obtain a formula for computing the Euler characteristic of a
Weil divisor D on a complete simplicial toric variety in terms of graded pieces
of the Cox ring and Stanley-Reisner ring. The main point is to use Alexander
duality to pass from the toric irrelevant ideal, which appears in the
computation of the Euler characteristic of D, to the Stanley-Reisner ideal of
the fan, which is used in defining the Chow ring. The formula also follows from
work of Maclagan-Smith.Comment: 9 pages 1 figur

### Hole doping dependences of the magnetic penetration depth and vortex core size in YBa2Cu3Oy: Evidence for stripe correlations near 1/8 hole doping

We report on muon spin rotation measurements of the internal magnetic field
distribution n(B) in the vortex solid phase of YBa2Cu3Oy (YBCO) single
crystals, from which we have simultaneously determined the hole doping
dependences of the in-plane Ginzburg-Landau (GL) length scales in the
underdoped regime. We find that Tc has a sublinear dependence on
1/lambda_{ab}^2, where lambda_{ab} is the in-plane magnetic penetration depth
in the extrapolated limits T -> 0 and H -> 0. The power coefficient of the
sublinear dependence is close to that determined in severely underdoped YBCO
thin films, indicating that the same relationship between Tc and the superfluid
density is maintained throughout the underdoped regime. The in-plane GL
coherence length (vortex core size) is found to increase with decreasing hole
doping concentration, and exhibit a field dependence that is explained by
proximity-induced superconductivity on the CuO chains. Both the magnetic
penetration depth and the vortex core size are enhanced near 1/8 hole doping,
supporting the belief by some that stripe correlations are a universal property
of high-Tc cuprates.Comment: 12 pages, 13 figure

### Delocalization of slowly damped eigenmodes on Anosov manifolds

We look at the properties of high frequency eigenmodes for the damped wave
equation on a compact manifold with an Anosov geodesic flow. We study
eigenmodes with spectral parameters which are asymptotically close enough to
the real axis. We prove that such modes cannot be completely localized on
subsets satisfying a condition of negative topological pressure. As an
application, one can deduce the existence of a "strip" of logarithmic size
without eigenvalues below the real axis under this dynamical assumption on the
set of undamped trajectories.Comment: 28 pages; compared with version 1, minor modifications, add two
reference

### Magnetic phase transition in V2O3 nanocrystals

V2O3 nanocrystals can be synthesized through hydrothermal reduction of
VO(OH)2 using hydrazine as a reducing agent. Addition of different ligands to
the reaction produces nanoparticles, nanorods and nanoplatelets of different
sizes. Small nanoparticles synthesized in this manner show suppression of the
magnetic phase transition to lower temperatures. Using muon spin relaxation
spectroscopy and synchrotron x-ray diffraction, it is determined that the
volume fraction of the high-temperature phase, characterized by a rhombohedral
structure and paramagnetism, gradually declines with decreasing temperature, in
contrast to the sharp transition observed in bulk V2O3.Comment: 6 pages, 6 figure

### Observation of non-exponential magnetic penetration profiles in the Meissner state - A manifestation of non-local effects in superconductors

Implanting fully polarized low energy muons on the nanometer scale beneath
the surface of a superconductor in the Meissner state enabled us to probe the
evanescent magnetic field profile B(z)(0<z<=200nm measured from the surface).
All the investigated samples [Nb: kappa \simeq 0.7(2), Pb: kappa \simeq 0.6(1),
Ta: kappa \simeq 0.5(2)] show clear deviations from the simple exponential B(z)
expected in the London limit, thus revealing the non-local response of these
superconductors. From a quantitative analysis within the Pippard and BCS models
the London penetration depth lambda_L is extracted. In the case of Pb also the
clean limit coherence length xi0 is obtained. Furthermore we find that the
temperature dependence of the magnetic penetration depth follows closely the
two-fluid expectation 1/lambda^2 \propto 1-(T/T_c)^4. While B(z) for Nb and Pb
are rather well described within the Pippard and BCS models, for Ta this is
only true to a lesser degree. We attribute this discrepancy to the fact that
the superfluid density is decreased by approaching the surface on a length
scale xi0. This effect, which is not taken self-consistently into account in
the mentioned models, should be more pronounced in the lowest kappa regime
consistently with our findings.Comment: accepted in PRB 14 pages, 17 figure

### Muon spin rotation and relaxation in magnetic materials

A review of the muon spin rotation and relaxation ($\mu$SR) studies on
magnetic materials published from July 1993 is presented. It covers the
investigation of magnetic phase diagrams, of spin dynamics and the analysis of
the magnetic properties of superconductors. We have chosen to focus on selected
experimental works in these different topics. In addition, a list of published
works is provided.Comment: Review article, 59 pages, LaTeX with IoP macro

### Lattice Distortion and Octupole Ordering Model in CexLa1-xB6

Possible order parameters of the phase IV in CexLa1-xB6 are discussed with
special attention to the lattice distortion recently observed. A
\Gamma_{5u}-type octupole order with finite wave number is proposed as the
origin of the distortion along the [111] direction. The \Gamma_8 crystalline
electric field (CEF) level splits into three levels by a mean field with the
\Gamma_{5u} symmetry. The ground and highest singlets have the same quadrupole
moment, while the intermediate doublet has an opposite sign. It is shown that
any collinear order of \Gamma_{5u}-type octupole moment accompanies the
\Gamma_{5g}-type ferro-quadrupole order, and the coupling of the quadrupole
moment with the lattice induces the distortion. The cusp in the magnetization
at the phase transition is reproduced, but the internal magnetic field due to
the octupole moment is smaller than the observed one by an order of magnitude.Comment: 5 pages, 4 figures, submitted to J. Phys. Soc. Jp

### Observation of two time scales in the ferromagnetic manganite La(1-x)Ca(x)MnO(3), x = 0.3

We report new zero-field muon spin relaxation and neutron spin echo
measurements in ferromagnetic (FM) (La,Ca)MnO3 which taken together suggest two
spatially separated regions in close proximity possessing very different Mn-ion
spin dynamics. One region corresponds to an extended cluster which displays
'critical slowing down' near Tc and an increasing volume fraction below Tc. The
second region possesses more slowly fluctuating spins and a decreasing volume
fraction below Tc. These data are discussed in terms of the growth of small
polarons into overlapping regions of correlated spins below Tc, resulting in a
microscopically inhomogeneous FM transition.Comment: 10 pages, 3 figure

### Few smooth d-polytopes with n lattice points

We prove that, for fixed n there exist only finitely many embeddings of
Q-factorial toric varieties X into P^n that are induced by a complete linear
system. The proof is based on a combinatorial result that for fixed nonnegative
integers d and n, there are only finitely many smooth d-polytopes with n
lattice points. We also enumerate all smooth 3-polytopes with at most 12
lattice points. In fact, it is sufficient to bound the singularities and the
number of lattice points on edges to prove finiteness.Comment: 20+2 pages; major revision: new author, new structure, new result

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