  The superconducting nano-layer coating without insulator layer is studied.
The magnetic-field distribution and the forces acting on a vortex are derived.
Using the derived forces, the vortex-penetration field and the lower critical
magnetic field can be discussed. The vortex-penetration field is identical with
the multilayer coating, but the lower critical magnetic field is not. Forces
acting on a vortex from the boundary of two superconductors play an important
role in evaluations of the free energy.
