The electronic state of T'-type cuprates which exhibit superconductivity without doping was investigated by
polarized x-ray absorption spectroscopy (XAS) for T'-La2CuO4 and T'-(La,Y)2CuO4 thin film single-crystals.
The effect of oxygenation and deoxygenation on the near-edge structures evidences the two processes create
and remove apical oxygen defects that strongly suppress superconductivity. The near-edge spectra further
indicate that the deoxygenation, well known as a common prerequisite for superconductivity, also creates
in-plane oxygen defects, whose contribution to the n-type conduction and superconductivity without doping is
not ruled out. The observed local lattice distortion consistent with the neutron scattering experiment may
influence a long-range magnetic order favoring a metallic state without doping.
We have measured the amplitude of the 1D lattice modulation forming the stripe structure in the CuO2 plane of Bi2Sr2Ca2Cu2O8+y single crystals by EXAFS. The period of the 1D modulation of the CuO2 plane has been measured by Cu anomalous diffraction. The large anharmonic content of the 1D modulation clearly shows the formation of stripes of undistorted LTO lattice. The large amplitude of the local structure modulation in plane indicates the formation of sizable potential barrier due to the linear domain walls in the plane. The size of the stripes L is such that the Fermi level is tuned to the maximum of the density of states formed by the second subband. The tuning of the Fermi level at the shape resonance of the superlattice of quantum wires is proposed to be the mechanism for the amplification of the critical temperature in high Tc cuprate superconductors.
We have found that the structure of the CuO2 plane of Bi2Sr2CaCu2O8+y (Bi2212) is anisotropic. Experimental investigation of the Cu site configurations in the CuO2 plane of Bi2Sr2CaCu2O8+y (Bi2212) by XANES and EXAFS shows that the quasi 2D Fermi liquid is confined in a superlattice of quantum stripes of width L running in the x direction. We have found that the recently proposed mechanism to rise the critical temperature by the confinement of an electron gas in superlattices and tuning the Fermi level to a shape resonance is verified. In fact the component of the Fermi wavevector kFy in the y direction perpendicular satisfies the condition kFy equals 2(pi) /L in Bi2212. This resonance gives an amplification of the critical temperature Tc by a factor of order of 5 in comparison with the critical temperature of the homogeneous CuO2 plane estimated to be about 15 - 20 K.
A new concept of adaptive silicon crystal monochromator for high heat load insertion devices is proposed in order to dynamically correct the thermal distortion by piezoelectric translators as a function of beam power. Shapes and dimensions of cooling channel was optimized by testing various types of grooved crystals using a 27-pole wiggler magnet beamline. The results indicate that the cooling efficiency of grooved silicon crystals can be improved by replacing a conventional semicircular cooling channel with a flat cooling channel with an optimized dimension. The results of rocking curve measurement showed an energy resolution ((Delta) E/E approximately 2 X 10-4). A prototype of adaptive first crystal with grooves was fabricated using a new diffusion bond technique. It was found that the crystal surface was precisely bent to a radius of several hundred meters by a piezoelectric device. An adaptive approach to the second crystal using an inchworm mortor was presented for dynamical sagittal focusing for realizing the energy-independent horizontal focus.
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