Observation of Surface Andreev Bound States of Superfluid He 3 by Transverse Acoustic Impedance Measurements

What is it about?

Superfluid 3He provides a unique opportunity to investigate the topological surface states of the established spin-triplet p-wave superfluid. Superfluid 3He B-phase is categorized as a time-reversal invariant topological superfluid. Surface bound states should form due to the bulk-edge correspondence and be topologically protected. The bound states are predicted to be Majorana fermions satisfying the equivalence of the particle and anti-particle. This is the first systematic spectroscopic study of the surface bound states of the topological superfluids. Our measurement of Z indicated no gap opening at fermi energy even under disorder, supporting the topological stability of the surface states. We also confirmed a peculiar sub-gap structure which is thought to be a reflection of anomalous scattering of Majorana fermions off the disorder.

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Why is it important?

Usually, particles are localized by the disorder and gap appears at fermi energy. However, the topological surface states are not gappable in the presence of disorder. Our measurement of Z indicated no gap opening at fermi energy even under disorder, supporting the topological stability of the surface states. We also confirmed a peculiar sub-gap structure which is thought to be a reflection of anomalous scattering of Majorana fermions off the disorder.