  We have studied a three-unit-cell-thick YBa2Cu3O7-x (YBCO) superconducting
film grown on a slightly vicinal SrTiO3 substrate that was polished from the
(001) plane by a small miscut angle (less than 0.5 degrees). This produced, on
its surface, a linear array of single-unit-cell-height steps with a period
larger than 40 nm. A characteristic fault, with a displacement corresponding to
one-third of the c-axis length of YBCO, is generated in the film on each
substrate step, as observed by atomic force microscopy. Transport measurements
with current flows parallel and perpendicular to the fault show that the fault
serves as a superconducting weak link, as well as a unique one-dimensional
flux-pinning center in an applied magnetic field. In addition, a characteristic
fine structure is found in the flux-flow resistivity as a function of magnetic
field, the origin of which may be ascribed to a matching effect between the
periodically aligned faults and the flux lattice.
