8,401 research outputs found
What has NMR taught us about stripes and inhomogeneity?
The purpose of this brief invited paper is to summarize what we have (not)
learned from NMR on stripes and inhomogeneity in La{2-x}Sr{x}CuO{4}. We explain
that the reality is far more complicated than generally accepted.Comment: Accepted for publication in the Proceedings of the LT-23 Conference
(invited
^{59}Co NMR evidence for charge ordering below T_{CO}\sim 51 K in Na_{0.5}CoO_2
The CoO layers in sodium-cobaltates NaCoO may be viewed as
a spin triangular-lattice doped with charge carriers. The underlying
physics of the cobaltates is very similar to that of the high cuprates.
We will present unequivocal Co NMR evidence that below ,
the insulating ground state of the itinerant antiferromagnet
NaCoO () is induced by charge ordering.Comment: Phys. Rev. Lett. 100 (2008), in press. 4 figure
Proper Motions of H2O Masers in the Water Fountain Source IRAS 19190+1102
We report on the results of two epochs of Very Long Baseline Array (VLBA)
observations of the 22 GHz water masers toward IRAS 19190+1102. The water maser
emission from this object shows two main arc-shaped formations perpendicular to
their NE-SW separation axis. The arcs are separated by ~280 mas in position,
and are expanding outwards at an angular rate of 2.35 mas/yr. We detect maser
emission at velocities between -53.3 km/s to +78.0 km/s and there is a distinct
velocity pattern where the NE masers are blueshifted and the SW masers are
redshifted. The outflow has a three-dimensional outflow velocity of 99.8 km/s
and a dynamical age of about 59 yr. A group of blueshifted masers not located
along the arcs shows a change in velocity of more than 35 km/s between epochs,
and may be indicative of the formation of a new lobe. These observations show
that IRAS 19190+1102 is a member of the class of "water fountain"'
pre-planetary nebulae displaying bipolar structureComment: Accepted for publication in ApJ, corrected typo
Heisenberg's uncertainty principle for simultaneous measurement of positive-operator-valued measures
A limitation on simultaneous measurement of two arbitrary positive operator
valued measures is discussed. In general, simultaneous measurement of two
noncommutative observables is only approximately possible. Following Werner's
formulation, we introduce a distance between observables to quantify an
accuracy of measurement. We derive an inequality that relates the achievable
accuracy with noncommutativity between two observables. As a byproduct a
necessary condition for two positive operator valued measures to be
simultaneously measurable is obtained.Comment: 7 pages, 1 figure. To appear in Phys. Rev.
NMR Search for the Spin Nematic State in LaFeAsO Single Crystal
We report a 75-As single crystal NMR investigation of LaFeAsO, the parent
phase of a pnictide high Tc superconductor. We demonstrate that spin dynamics
develop a strong two-fold anisotropy within each orthorhombic domain below the
tetragonal-orthorhombic structural phase transition at T[TO]~156 K. This
intermediate state with a dynamical breaking of the rotational symmetry freezes
progressively into a spin density wave (SDW) below T[SDW]~142 K. Our findings
are consistent with the presence of a spin nematic state below T[TO] with an
incipient magnetic order.Comment: Revised manuscript accepted for publication in Phys. Rev. Let
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