  Vortices in two-dimensional superconductors with broken time-reversal and
spin-rotation symmetry can bind states at zero excitation energy. These
socalled Majorana bound states transform a thermal insulator into a thermal
metal and may be used to encode topologically protected qubits. We identify an
alternative mechanism for the formation of Majorana bound states, akin to the
way in which Shockley states are formed on metal surfaces: An atomic-scale
electrostatic line defect can have a pair of Majorana bound states at the end
points. The Shockley mechanism explains the appearance of a thermal metal in
vortex-free lattice models of chiral p-wave superconductors and (unlike the
vortex mechanism) is also operative in the topologically trivial phase.
