  We propose a semiconductor-superconductor hybrid device for realizing
topological superconductivity and Majorana zero modes consisting of a planar
Josephson junction structure with periodically modulated junction width. By
performing a numerical analysis of the effective model describing the
low-energy physics of the hybrid structure, we demonstrate that the modulation
of the junction width results in a substantial enhancement of the topological
gap and, consequently, of the robustness of the topological superconducting
phase and associated Majorana zero modes. This enhancement is due to the
formation of minibands with strongly renormalized effective parameters,
including stronger spin-orbit coupling, generated by the effective periodic
potential induced by the modulated structure. In addition to a larger
topological gap, the proposed device supports a topological superconducting
phase that covers a significant fraction of the parameter space, including the
low Zeeman field regime, in the absence of a superconducting phase difference
across the junction. Furthermore, the optimal regime for operating the device
can be conveniently accessed by tuning the potential in the junction region
using, for example, a top gate.
