Majorana edge modes of topological exciton condensate with superconductors

I study the edge states of the topological exciton condensate formed by Coulomb interaction between two parallel surfaces of a strong topological insulator. When the condensate is contacted by superconductors with a {\pi} phase shift across the two surfaces, a pair of counter-propagating Majorana modes close the gap at the boundary. I propose a nano-structured system of topological insulators and superconductors to realize unpaired Majorana fermions. The Majorana signal can be used to detect the formation of the topological exciton condensate. The relevant experimental signatures as well as implications for related systems are discussed.Comment: 4 pages, 4 figures; (v2) Eq. 7 and Fig. 4 and various typos corrected. All conclusions remain the sam

Zero modes of the generalized fermion-vortex system in magnetic field

We show that Dirac fermions moving in two spatial dimensions with a generalized dispersion $E\sim p^N$, subject to an external magnetic field and coupled to a complex scalar field carrying a vortex defect with winding number $Q$ acquire $NQ$ zero modes. This is the same as in the absence of the magnetic field. Our proof is based on selection rules in the Landau level basis that dictate the existence and the number of the zero modes. We show that the result is insensitive to the choice of geometry and is naturally extended to general field profiles, where we also derive a generalization of the Aharonov-Casher theorem. Experimental consequences of our results are briefly discussed.Comment: 4 pages, 1 fig and 4+ pages, 3 figs (supplemental

Proposed Aharonov-Casher interference measurement of non-Abelian vortices in chiral p-wave superconductors

We propose a two-path vortex interferometry experiment based on the Aharonov-Casher effect for detecting the non-Abelian nature of vortices in a chiral p-wave superconductor. The effect is based on observing vortex interference patterns upon enclosing a finite charge of externally controllable magnitude within the interference path. We predict that when the interfering vortices enclose an odd number of identical vortices in their path, the interference pattern disappears only for non-Abelian vortices. When pairing involves two distinct spin species, we derive the mutual statistics between half quantum and full quantum vortices and show that, remarkably, our predictions still hold for the situation of a full quantum vortex enclosing a half quantum vortex in its path. We discuss the experimentally relevant conditions under which these effects can be observed.Comment: 4 pages, 1 figur