Unpaired Majorana Modes in Josephson-Junction Arrays with Gapless Bulk Excitations

Phys Rev Lett. 2015 Nov 6;115(19):197001. doi: 10.1103/PhysRevLett.115.197001. Epub 2015 Nov 6.

Abstract

The search for Majorana bound states in solid-state physics has been limited to materials that display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson-junction arrays with gapless bulk excitations. The bulk modes mediate a coupling between Majorana bound states via the Ruderman-Kittel-Yosida-Kasuya mechanism. As a consequence, the lowest energy doublet acquires a finite energy difference. For a realistic set of parameters this energy splitting remains much smaller than the energy of the bulk eigenstates even for short chains of length L∼10.