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

• Published in: arXiv.org 2017-01
• Main Authors: Khezerlou, Maryam, Goudarzi, Hadi, Samin Asgarifar
• Format: Article
• Language: English
• Subjects: Critical current (superconductivity); Crossovers; Dependence; Ferromagnetism; Holes (electron deficiencies); Incidence angle; Josephson junctions; Superconductivity; Topological insulators; Topology
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1701.08277

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 \(\eta(m_{zfs})\), 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.