Zero-energy pinning from interactions in Majorana nanowires

Majorana zero modes at the boundaries of topological superconductors are charge-neutral, an equal superposition of electrons and holes. This ideal situation is, however, hard to achieve in physical implementations, such as proximitized semiconducting nanowires of realistic length. In such systems Majorana overlaps are unavoidable and lead to their hybridization into charged Bogoliubov quasiparticles of finite energy, which, unlike true zero modes, are affected by electronic interactions. We here demonstrate that these interactions, particularly with bound charges in the dielectric surroundings, drastically change the non-interacting paradigm. Remarkably, interactions may completely suppress Majorana hybridization around parity crossings, where the total charge in the nanowire changes. This effect, dubbed zero-energy pinning, stabilizes Majoranas back to zero energy and charge, and leads to electronically incompressible parameter regions wherein Majoranas remain insensitive to local perturbations, despite their overlap. Condensed-matter physics: zero-energy pinning of Majoranas Majorana zero modes are quasiparticle excitations which are charge neutral at the boundaries of topological superconductors. Their practical generation in semiconducting nanowires of realistic length often faces Majorana overlaps leading to charged states that are no longer topologically protected against electrostatic interactions with the environment. Now, a team of researchers in Spain from Autonomous University of Madrid and Institute of Materials Science of Madrid, CSIC, demonstrates that the electrostatic environment may be engineered so that interactions fully suppress Majorana hybridization around parity crossings. That is, zero-energy crossings are stabilized into regions in parameter space where Majoranas become pinned to zero energy. The zero splitting of non-overlapping Majoranas, commonly associated to topological protection and to applications in topological quantum computation, can occur in spite of the Majorana overlap in nanowires of finite length. The generic zero-energy pinning mechanism could be extended to other contexts such as parity crossings of Shiba states in non-topological superconductors.