8,401 research outputs found

    What has NMR taught us about stripes and inhomogeneity?

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    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

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    The CoO2_{2} layers in sodium-cobaltates Nax_{x}CoO2_{2} may be viewed as a spin S=1/2S=1/2 triangular-lattice doped with charge carriers. The underlying physics of the cobaltates is very similar to that of the high TcT_{c} cuprates. We will present unequivocal 59^{59}Co NMR evidence that below TCO51KT_{CO}\sim51 K, the insulating ground state of the itinerant antiferromagnet Na0.5_{0.5}CoO2_{2} (TN86KT_{N}\sim 86 K) 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

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    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

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    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

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    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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