One of the leading issues in high-T(c) superconductors is the origin of the pseudogap phase in underdoped cuprates. Using polarized elastic neutron diffraction, we identify a novel magnetic order in the YB(2)Cu(3)O(6+) system. The observed magnetic order preserves translational symmetry of the lattice as proposed for orbital moments in the circulating current theory of the pseudogap state. To date, it is the first direct evidence of a hidden order parameter characterizing the pseudogap phase in high-T(c) cuprates.

YBa2Cu3Oy (Y123) bulk materials were textured with artificially patterned holes, creating a ‘perforated structure’. The goal is to facilitate sample oxygenation and decrease crack formation in order to address the problem of hot spot formation in fault current limiter (FCL) applications. As-processed samples contained mechanically patterned holes parallel to the mean c-axis interconnected to the textured domain. This makes samples easier to oxygenate and cool. The microstructure is not distorted in the vicinity of the holes. The single domain character of the sample is evidenced by XRD pole figure investigations. Meander tracks were prepared by drilling the upper and lower surfaces of the samples. Samples containing holes still trap high fields, comparable with samples without holes. Values of Jc are increased in samples with holes.

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Using elastic neutron scattering, we evidence a commensurate antiferromagnetic Cu(2) order (AF) in the superconducting (SC) high-$\rm T_c$ cuprate $\rm YBa_2(Cu_{1-y}Co_y)_3O_{7+\delta}$ (y=0.013, $\rm T_c$=93 K). As in the Co-free system, the spin excitation spectrum is dominated by a magnetic resonance peak at 41 meV but with a reduced spectral weight. The substitution of Co thus leads to a state where AF and SC cohabit showing that the CuO$_2$ plane is a highly antiferromagnetically polarizable medium even for a sample where T$_c$ remains optimum.Comment: 3 figure