Extensive small angle neutron scattering experiments have been conducted on the vortex system in YBa2Cu3O7 in a magnetic field range of 0.5 T≤H≤5 T, and with various orientations of the magnetic field with respect to the crystallographic axes. For H parallel to the c axis, the vortex lattice is oblique with two nearly equal lattice constants and an angle of 73°between primitive vectors. One principal axis of the vortex lattice coincides with the (110) direction of the crystal lattice. It is shown that this structure cannot be explained in the framework of a purely electrodynamic (London) model, and that it is intimately related to the in-plane anisotropy of the superconducting coherence length. When the field is inclined with respect to the c axis, the uniaxial anisotropy due to the layered crystal structure of YBa2Cu3O7 becomes relevant. The interplay between the square in-plane anisotropy and the uniaxial anisotropy leads to both a continous structural transition and a reorientation of the vortex lattice as a function of inclination angle. For the largest inclination angles, the vortex lattice decomposes into independent chains.


Materials Science and Engineering

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© 1994 American Institute of Physics (AIP), All rights reserved.

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01 Jan 1994