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Abstract

We report the observation of the flux line lattice in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ by scanning tunneling microscopy. The measurements were carried out at 4.2 K and in a magnetic field of 6 T applied along the $c$ axis. The vortices appear arranged in an oblique lattice in which the primitive vectors are nearly equal and form an angle of approximately 77\ifmmode^\circ\else\textdegree\fi{}. We also report local tunneling spectroscopy into a vortex core which reveals two peaks separated by about 11 meV. The zero-field spectra are reproducible over large areas of the sample and show a multiple peak structure.