Dispersive excitations in the high-temperature superconductor La2-xSrxCuO4

High-resolution neutron scattering experiments on optimally doped La2-xSrxCuO4 (x=0.16) reveal that the magnetic excitations are dispersive. The dispersion is the same as in YBa2Cu3O6.85, and is quantitatively related to that observed with charge sensitive probes. The associated velocity in La2-xSrxCuO4 is only weakly dependent on doping with a value close to the spin-wave velocity of the insulating (x=0) parent compound. In contrast with the insulator, the excitations broaden rapidly with increasing energy, forming a continuum at higher energy and bear a remarkable resemblance to multiparticle excitations observed in 1D S=1/2 antiferromagnets. The magnetic correlations are 2D, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting 1D magnets.     

SnO2 nanowires mixed nanodendrites for high ethanol sensor response

Mixed morphology of SnO₂ nanowires and nanodendrites was synthesized on the gold-coated alumina substrates by carbothermal reduction of SnO₂ in closed crucible. The products were characterized by scanning electron microscopy, x-ray diffractometer, and transmission electron microscopy. Results showed the SnO₂ nanowires and the SnO₂ nanodendrites branched out from the main nanowires. Both SnO₂ nanostructures were pure tetragonal rutile structure. The nanowires were grown in [101] and directions with the diameter of 50–150 nm and the length of a few 10 μm. The nanodendrites were about 100–300 nm in diameter. The growth mechanism of the SnO₂ nanostructures was also discussed. Characterization of ethanol gas sensor, based on the mixed morphology of the SnO₂ nanostructures, was carried out. The optimal temperature was about 360 °C and the sensor response was 120 for 1000 ppm of ethanol concentration.