A vortex lattice consisting of a pinstripe pattern of vortex chains has been observed in untwinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ crystals. This state is present when the field is tilted away from the c^ axis, and is oriented with the chains confined to the plane defined by B and c^. The chains arise from the attractive part of the vortex-vortex interaction in this geometry as described within the ansiotropic London equations. For B>${\mathrm{\Phi }}_0$/2πλ̃ ${}_{}{}^2{}_{}{}^{}$ the chains merge into an oriented vortex lattice. From the fitted value of λ̃, we can conclude that the microscopic irreversibility temperature is T/${\mathit{T}}_{\mathit{c}}$∼0.92 for B∼20 G.

• Received 18 March 1992

DOI:https://doi.org/10.1103/PhysRevLett.68.3343