📝 SummarXiv

Abstract

The Rashba effect--a momentum-dependent spin splitting from broken inversion symmetry--is a crucial component for engineering topological superconductors (TSCs). However, time-reversal invariant TSCs based on conventional linear Rashba spin-orbit coupling (RSOC) are fundamentally restricted to a helical $p$-wave state, hosting only a single Majorana Kramers pair. In this Letter, we demonstrate that the unique triple-winding spin texture of cubic RSOC offers a direct pathway to surpass this limitation. We propose a bilayer model where the synergy of cubic RSOC and an intrinsic odd-parity pairing instability yields a rare 2D helical $f$-wave TSC. This state is characterized by a large mirror Chern number (MCN) ${\cal N}_{\text{M}}=3$ and hosts three Kramers pairs of Majorana edge modes. Furthermore, the interplay of linear and cubic RSOCs can yield a hybrid helical $p+f$-wave TSC with an even larger MCN of ${\cal N}_{\text{M}}=4$. Our work establishes higher-order spin-orbit coupling as a powerful design principle for realizing TSCs with multiple Majorana Kramers channels, holding immediate relevance for tunable platforms like oxide heterostructures.