Are Rashba Effects Essential for Topological Planar Josephson Junctions?

Rashba spin–orbit coupling is widely regarded as a key ingredient for realizing Majorana modes in planar Josephson junctions. Here we challenge this conventional wisdom by introducing a centrosymmetric, Rashba-free mechanism for achieving topological Josephson junctions with conventional spin-singlet s-wave superconductors. We show that when the parent superconductor hosts topological bands in its normal state, an in-plane magnetic field can induce Majorana physics near certain critical doping levels. This mechanism applies broadly to systems with stable or fragile topological bands, as well as those with obstructed atomic bands. Our theory reveals an intrinsic link between the topology of normal-state electrons and that of Andreev bound states, establishing a new framework to design, explore, and engineer topological superconductivity in planar junctions.