Engineering helical superconductors with multiple Majorana Kramers pairs via higher-order Rashba spin-orbit coupling

Abstract

The momentum dependence of Rashba spin-orbit coupling (RSOC) is a key ingredient for engineering topological superconductors (TSCs), yet research has overwhelmingly focused on its linear-in-momentum form. This focus has restricted time-reversal invariant TSCs to helical p-wave states, which are characterized by a Z2 topological invariant that permits at most a single Majorana Kramers pair at a given boundary. Their existence has also been tied to the stringent criterion of an odd number of Fermi surfaces (FSs). In this work, we establish higher-order RSOC as a powerful design principle to go beyond the Z2 classification and the odd-FS criterion. We demonstrate that a bilayer system with a pure cubic RSOC and an intrinsic odd-parity pairing on a single FS yields a rare 2D helical f wave TSC. This state is characterized by a large mirror Chern number (MCN) of NM=3 and hosts three Kramers pairs of Majorana edge modes. Remarkably, the interplay of linear and cubic RSOCs in this bilayer can generate a helical hybrid p+f-wave TSC with an even larger MCN of NM=4 from a normal state with two FSs, thereby circumventing the conventional odd-FS criterion. Our work establishes higher-order RSOC as a “topology multiplier” for realizing TSCs with multiple Majorana Kramers channels, fundamentally reshapes the criteria for helical TSCs, and holds immediate relevance for tunable platforms like oxide heterostructures.

Source-reported materials — not catalogue approval

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