  Majorana zero modes (MZMs) are of central importance for modern condensed
matter physics and quantum information due their non-Abelian nature, which
thereby offers the possibility of realizing topological quantum bits. We here
show that a grain boundary (GB) defect can host a topological superconductor
(SC), with a pair of cohabitating MZMs at its end when immersed in a parent
two-dimensional gapped topological SC with the Fermi surface enclosing a
nonzero momentum. The essence of our proposal lies in the magnetic-field driven
hybridization of the localized MZMs at the elementary blocks of the GB defect,
the single lattice dislocations, due to the MZM spin being locked to the
Burgers vector. Indeed, as we show through numerical and analytical
calculations, the GB topological SC with two localized MZMs emerges in a finite
range of both the angle and magnitude of the external magnetic field. Our work
demonstrates the possibility of defect-based platforms for quantum information
technology and opens up a route for their systematic search in future.
