Anisotropic vortex structure in Y1Ba2Cu3O7.

Abstract

We report Bitter-pattern observations of the vortices for flux trapped in crystals of the orthorhombic high-${\mathrm{T}}_{\mathrm{c}}$ superconductor ${\mathrm{Y}}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. For B\ensuremath{\parallel}c axis, the slight distortion of the vortex lattice yields a penetration-depth anisotropy ranging from 1.11 to 1.15 for different crystals. For B\ensuremath{\perp}c, the case of strong anisotropy, we observe chains of oval vortices. When they are not aligned by defects, the chains appear to undulate rather than adopt a crystalline habit. From the vortex spacing we deduce an anisotropy of 5.5\ifmmode\pm\else\textpm\fi{}1.