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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 π 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.