Takehito Yokoyama

Unconventional superconductivity on a topological insulator.

We study proximity-induced superconductivity on the surface of a topological insulator (TI), focusing on unconventional pairing. We find that the excitation spectrum becomes gapless for any spin-triplet pairing, such that both subgap bound states and Andreev reflection is strongly suppressed. For spin-singlet pairing, the zero-energy surface state in the d(xy)-wave case becomes a Majorana fermion, in contrast with the situation realized in the topologically trivial high-T(c) cuprates. We also study the influence of a Zeeman field on the surface states. Both the magnitude and direction of this field are shown to strongly influence the transport properties, in contrast with the case without TI. We predict an experimental signature of the Majorana states via conductance spectroscopy.

Manipulation of the Majorana Fermion, Andreev Reflection, and Josephson Current on Topological Insulators

We study theoretically the transport properties of a normal metal (N)/ferromagnet insulator (FI)/superconductor (S) junction and a S/FI/S junction formed on the surface of a three-dimensional topological insulator, where the chiral Majorana mode exists at the FI/S interface. We find the chiral Majorana mode generated in N/FI/S and S/FI/S junctions is very sensitively controlled by the direction of the magnetization m in the FI region. In particular, the current-phase relation of the Josephson current in S/FI/S junctions has a phase shift of neither 0 nor pi that can be tuned continuously by the component of m perpendicular to the interface.

Anomalous finite size effects on surface states in the topological insulator Bi 2 Se 3

We study how the surface states in the strong topological insulator

Controllable spin transport in ferromagnetic graphene junctions

{\text{Bi}}_{2}{\text{Se}}_{3}

Controllable valley and spin transport in ferromagnetic silicene junctions

are influenced by finite size effects and compare our results with those recently obtained for two-dimensional topological insulator HgTe. We demonstrate two important distinctions: (i) contrary to HgTe, the surface states in

Topology of Andreev bound states with flat dispersion

{\text{Bi}}_{2}{\text{Se}}_{3}

Theory of topological spin current in noncentrosymmetric superconductors

display a remarkable robustness towards decreasing the width

Theoretical study of the dynamics of magnetization on the topological surface

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Interplay between superconductivity and ferromagnetism on a topological insulator

down to a few nm thus ensuring that the topological surface states remain intact and (ii) the gapping due to the hybridization of the surface states features an oscillating exponential decay as a function of

Anomalous Andreev bound state in noncentrosymmetric superconductors.

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