Proximity-Induced Superconducting States of Magnetically Doped 3D Topological Insulators with High Bulk Insulation

Abstract

We studied magnetized topological insulator/superconductor junctions with the expectation of unconventional superconductive states holding Majorana fermions induced by superconductive proximity effects on the surface states of magnetized topological insulators (TIs), attached by conventional superconductors. We introduced Fe-doped BiSbTe2Se as an ideal magnetic TI and used the developed junction fabrication process to access the proximity-induced surface superconducting states. The bulk single crystals of the Fe-doped TI showed excellent bulk-insulating properties and ferromagnetism simultaneously at a low temperature. Meanwhile, the fabricated junctions also showed an insulating behavior above 100 K, as well as metallic conduction at a low temperature, which reflects bulk carrier freezing. In addition, we observed a proximity-induced gap structure in the conductance spectra. These results indicate that the junctions using the established materials and process are preferable to observe unconventional superconducting states which are induced via the surface channels of the magnetized TI. We believe that the developed process can be applied for the fabrication of complicated junctions and suites for braiding operations.

Revealing Intrinsic Superconductivity of the Nb/BiSbTe2Se Interface

“…We studied Fe‐doped 3D topological insulator BiSbTe 2 Se (Fe‐BSTS), synthesized by the modified Bridgman method. [ 15 ] High‐resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) image of the Fe‐BSTS is shown in Figure a. The electron diffraction image corresponds to the rhombohedral crystal structure with lattice constants a = 4.2 Å and c = 29.7 Å, which is consistent with previous measurements of similar TIs.…”

Measuring the Electron–Phonon Interaction in Two-Dimensional Superconductors with He-Atom Scattering

“…Layered pnictogen chalcogenides, with a bulk electronic band gap and a cone of topological Dirac states localized at the surface and crossing the Fermi level, are topological insulators (TI) unsuitable to be superconductors at any temperature. They can however become so by intercalating donor atoms [87][88][89], doping [90], by interfacing with conventional superconductors via the proximity effect [91][92][93][94][95][96], or under pressure [97][98][99]. Although critical temperatures of induced superconductivity are in the best cases in the range of a few Kelvin, the involvement of surface topologically protected states confers a particular stability against external disturbances.…”

Theory of the Josephson current on a magnetically doped topological insulator

“…1, and discuss how the existence of the chiral Majorana modes affects the Josephson current. Recently, there is a report on the experimental realization of Josephson junctions on magnetically doped TIs 30,31 . In magnetically doped TIs, the energy dispersion of the surface Dirac electron has a gap opening when the direction of the magnetization is perpendicular to the surface and its magnitude is larger than the chemical potential of surface Dirac electron µ.…”