Edge mass current and roles of Majorana Fermions in superfluid 3He A-phase

Abstract

The total angular momentum associated with the edge mass current flowing at the boundary in the superfluid $^3$He A-phase confined in a disk is proved to be $L=N\hbar/2$, consisting of $L^{\rm MJ}=N\hbar$ from the Majorana quasi-particles (QPs) and $L^{\rm cont}=-N\hbar/2$ from the continuum state. We show it based on an analytic solution of the chiral order parameter for quasi-classical Eilenberger equation. Important analytic expressions are obtained for mass current, angular momentum, and density of states (DOS). Notably the DOS of the Majorana QPs is exactly $N_0/2$ ($N_0$: normal state DOS) responsible for the factor 2 difference between $L^{\rm MJ}$ and $L^{\rm cont}$. The current decreases as $E^{-3}$ against the energy $E$, and $L(T) \propto -T^2$. This analytic solution is fully backed up by numerically solving the Eilenberger equation. We touch on the so-called intrinsic angular momentum problem.