12,715 research outputs found
(63)Cu NQR Evidence for Spatial Variation of Hole Concentration in La(2-x)Sr(x)CuO(4)
We report experimental evidence for the spatial variation of hole
concentration x_(hole) in the high Tc superconductor La(2-x)Sr(x)CuO(4) (0.04
<= x <= 0.16) by using (63)Cu NQR for (63)Cu isotope enriched samples. We
demonstrate that the extent of the spatial variation of the local hole
concentration D(x)_(hole) is reflected on (63)1/T1 and deduce the temperature
dependence. D(x)_(hole) increases below 500 - 600K, and reaches values as large
as D(x)_(hole)/x ~ 0.5 below ~ 150K. We estimate the length scale of the
spatial variation in x_(hole) to be R_(hole) >~ 3nm from analysis of the NQR
spectrum.Comment: Accepted for publication in Physical Review Letter
Collective excitations and instability of an optical lattice due to unbalanced pumping
We solve self-consistently the coupled equations of motion for trapped
particles and the field of a one-dimensional optical lattice. Optomechanical
coupling creates long-range interaction between the particles, whose nature
depends crucially on the relative power of the pump beams. For asymmetric
pumping, traveling density wave-like collective oscillations arise in the
lattice, even in the overdamped limit. Increasing the lattice size or pump
asymmetry these waves can destabilize the lattice.Comment: 5 pages, minor changes (SI units, new references
More than Three Laws of Robotics
Wired for War: The Robotics Revolution and Conflict in the 21st Centur
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