Dominant Majorana bound energy and critical current enhancement in ferromagnetic-superconducting topological insulator

• Published in: The European physical journal. B, Condensed matter physics Condensed matter physics, 2017-03, Vol.90 (3), p.1-8, Article 44
• Main Authors: Khezerlou, Maryam, Goudarzi, Hadi, Asgarifar, Samin
• Format: Article
• Language: English
• Subjects: Complex Systems; Condensed Matter Physics; Critical current (superconductivity); Ferromagnetism; Fluid- and Aerodynamics; Holes (electron deficiencies); Incidence angle; Josephson junctions; Magnetic properties; Magnetization; Physics; Physics and Astronomy; Regular Article; Solid State Physics; Superconductivity; Superconductors; Topological insulators
• ISSN: 1434-6028; 1434-6036
• DOI: 10.1140/epjb/e2017-70596-7

Among the potential applications of topological insulators, we theoretically study the coexistence of proximity-induced ferromagnetic and superconducting orders in the surface states of a 3-dimensional topological insulator. The superconducting electron-hole excitations can be significantly affected by the magnetic order induced by a ferromagnet. In one hand, the surface state of the topological insulator, protected by the time-reversal symmetry, creates a spin-triplet and, on the other hand, magnetic order causes to renormalize the effective superconducting gap. We find Majorana mode energy along the ferromagnet/superconductor interface to sensitively depend on the magnitude of magnetization m zfs from superconductor region, and its slope around perpendicular incidence is steep with very low dependency on m zfs . The superconducting effective gap is renormalized by a factor η ( m zfs ), and Andreev bound state in ferromagnet-superconductor/ferromagnet/ferromagnet-superconductor (FS/F/FS) Josephson junction is more sensitive to the magnitude of magnetizations of FS and F regions. In particular, we show that the presence of m zfs has a noticeable impact on the gap opening in Andreev bound state, which occurs in finite angle of incidence. This directly results in zero-energy Andreev state being dominant. By introducing the proper form of corresponding Dirac spinors for FS electron-hole states, we find that via the inclusion of m zfs , the Josephson supercurrent is enhanced and exhibits almost abrupt crossover curve, featuring the dominant zero-energy Majorana bound states.