Surface Majorana Cone of the Superfluid $^3$He B Phase

The superfluid $^3$He B phase, one of the oldest unconventional fermionic condensates experimentally realized, is recently predicted to support Majorana fermion surface states. Majorana fermion, which is characterized by the equivalence of particle and antiparticle, has a linear dispersion relation referred to as the Majorana cone. We measured the transverse acoustic impedance $Z$ of the superfluid$^3$He B phase changing its boundary condition and found a growth of peak in $Z$ on a higher specularity wall. Our theoretical analysis indicates that the variation of $Z$ is induced by the formation of the cone-like dispersion relation and thus confirms the important feature of the Majorana fermion in the specular limit.