419 research outputs found
Quantum Impurities in the Two-Dimensional Spin One-Half Heisenberg Antiferromagnet
The study of randomness in low-dimensional quantum antiferromagnets is at the
forefront of research in the field of strongly correlated electron systems, yet
there have been relatively few experimental model systems. Complementary
neutron scattering and numerical experiments demonstrate that the spin-diluted
Heisenberg antiferromagnet La2Cu(1-z)(Zn,Mg)zO4 is an excellent model material
for square-lattice site percolation in the extreme quantum limit of spin
one-half. Measurements of the ordered moment and spin correlations provide
important quantitative information for tests of theories for this complex
quantum-impurity problem.Comment: 11 pages, 3 figures. NOTE: possible errors in PDF version of Fig. 1.
View postscript version of figure if possibl
Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}
High-transition-temperature (high-Tc) superconductivity develops near
antiferromagnetic phases, and it is possible that magnetic excitations
contribute to the superconducting pairing mechanism. To assess the role of
antiferromagnetism, it is essential to understand the doping and temperature
dependence of the two-dimensional antiferromagnetic spin correlations. The
phase diagram is asymmetric with respect to electron and hole doping, and for
the comparatively less-studied electron-doped materials, the antiferromagnetic
phase extends much further with doping [1, 2] and appears to overlap with the
superconducting phase. The archetypical electron-doped compound
Nd{2-x}Ce{x}CuO{4\pm\delta} (NCCO) shows bulk superconductivity above x \approx
0.13 [3, 4], while evidence for antiferromagnetic order has been found up to x
\approx 0.17 [2, 5, 6]. Here we report inelastic magnetic neutron-scattering
measurements that point to the distinct possibility that genuine long-range
antiferromagnetism and superconductivity do not coexist. The data reveal a
magnetic quantum critical point where superconductivity first appears,
consistent with an exotic quantum phase transition between the two phases [7].
We also demonstrate that the pseudogap phenomenon in the electron-doped
materials, which is associated with pronounced charge anomalies [8-11], arises
from a build-up of spin correlations, in agreement with recent theoretical
proposals [12, 13].Comment: 5 pages, 4 figure
Fine structure of alpha decay in odd nuclei
Using an alpha decay level scheme, an explanation for the fine structure in
odd nuclei is evidenced by taking into account the radial and rotational
couplings between the unpaired nucleon and the core of the decaying system. It
is stated that the experimental behavior of the alpha decay fine structure
phenomenon is directed by the dynamical characteristics of the system.Comment: 8 pages, 3 figures, REVTex, submitted to Physical Review
An interferometric complementarity experiment in a bulk Nuclear Magnetic Resonance ensemble
We have experimentally demonstrated the interferometric complementarity,
which relates the distinguishability quantifying the amount of which-way
(WW) information to the fringe visibility characterizing the wave feature
of a quantum entity, in a bulk ensemble by Nuclear Magnetic Resonance (NMR)
techniques. We primarily concern on the intermediate cases: partial fringe
visibility and incomplete WW information. We propose a quantitative measure of
by an alternative geometric strategy and investigate the relation between
and entanglement. By measuring and independently, it turns out that
the duality relation holds for pure quantum states of the
markers.Comment: 13 page, 5 PS figure
Phase Decomposition and Chemical Inhomogeneity in Nd2-xCexCuO4
Extensive X-ray and neutron scattering experiments and additional
transmission electron microscopy results reveal the partial decomposition of
Nd2-xCexCuO4 (NCCO) in a low-oxygen-fugacity environment such as that typically
realized during the annealing process required to create a superconducting
state. Unlike a typical situation in which a disordered secondary phase results
in diffuse powder scattering, a serendipitous match between the in-plane
lattice constant of NCCO and the lattice constant of one of the decomposition
products, (Nd,Ce)2O3, causes the secondary phase to form an oriented,
quasi-two-dimensional epitaxial structure. Consequently, diffraction peaks from
the secondary phase appear at rational positions (H,K,0) in the reciprocal
space of NCCO. Additionally, because of neodymium paramagnetism, the
application of a magnetic field increases the low-temperature intensity
observed at these positions via neutron scattering. Such effects may mimic the
formation of a structural superlattice or the strengthening of
antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified
through careful and systematic experimentation. For typical reduction
conditions, the (Nd,Ce)2O3 volume fraction is ~1%, and the secondary-phase
layers exhibit long-range order parallel to the NCCO CuO2 sheets and are 50-100
angstromsthick. The presence of the secondary phase should also be taken into
account in the analysis of other experiments on NCCO, such as transport
measurements.Comment: 15 pages, 17 figures, submitted to Phys. Rev.
On the decay of deformed actinide nuclei
decay through a deformed potential barrier produces significant
mixing of angular momenta when mapped from the nuclear interior to the outside.
Using experimental branching ratios and either semi-classical or
coupled-channels transmission matrices, we have found that there is a set of
internal amplitudes which are essentially constant for all even--even actinide
nuclei. These same amplitudes also give good results for the known anisotropic
particle emission of the favored decays of odd nuclei in the same mass
region.
PACS numbers: 23.60.+e, 24.10.Eq, 27.90.+bComment: 5 pages, latex (revtex style), 2 embedded postscript figures
uuencoded gz-compressed .tar file To appear in Physical Review Letter
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