Abolhassan Vaezi

Spin-transfer torque generated by a topological insulator

Magnetic devices are a leading contender for the implementation of memory and logic technologies that are non-volatile, that can scale to high density and high speed, and that do not wear out. However, widespread application of magnetic memory and logic devices will require the development of efficient mechanisms for reorienting their magnetization using the least possible current and power. There has been considerable recent progress in this effort; in particular, it has been discovered that spin–orbit interactions in heavy-metal/ferromagnet bilayers can produce strong current-driven torques on the magnetic layer, via the spin Hall effect in the heavy metal or the Rashba–Edelstein effect in the ferromagnet. In the search for materials to provide even more efficient spin–orbit-induced torques, some proposals have suggested topological insulators, which possess a surface state in which the effects of spin–orbit coupling are maximal in the sense that an electron’s spin orientation is fixed relative to its propagation direction. Here we report experiments showing that charge current flowing in-plane in a thin film of the topological insulator bismuth selenide (Bi2Se3) at room temperature can indeed exert a strong spin-transfer torque on an adjacent ferromagnetic permalloy (Ni81Fe19) thin film, with a direction consistent with that expected from the topological surface state. We find that the strength of the torque per unit charge current density in Bi2Se3 is greater than for any source of spin-transfer torque measured so far, even for non-ideal topological insulator films in which the surface states coexist with bulk conduction. Our data suggest that topological insulators could enable very efficient electrical manipulation of magnetic materials at room temperature, for memory and logic applications.

Fractional topological superconductors with fractionalized Majorana fermions

In this paper, we introduce a two-dimensional fractional topological superconductor (FTSC) as a strongly correlated topological state which can be achieved by inducing superconductivity into an Abelian fractional quantum Hall state, through the proximity effect. When the proximity coupling is weak, the FTSC has the same topological order as its parent state and is thus Abelian. However, upon increasing the proximity coupling, the bulk gap of such an Abelian FTSC closes and reopens resulting in a new topological order: a non-Abelian FTSC. Using several arguments we will conjecture that the conformal field theory (CFT) that describes the edge state of the non-Abelian FTSC is

Topological superconductivity in monolayer transition metal dichalcogenides

U(1)/Z_2

Topological electric current from time-dependent elastic deformations in graphene

orbifold theory and use this to write down the ground-state wave function. Further, we predict FTSC based on the Laughlin state at

Non-Abelian phases in two-component

\nu=1/m

\nu=2/3

filling to host fractionalized Majorana zero modes bound to superconducting vortices. These zero modes are non-Abelian quasiparticles which is evident in their quantum dimension of

fractional quantum Hall states: Emergence of Fibonacci anyons

d_m=\sqrt{2m}

Phase diagram of the strongly correlated Kane-Mele-Hubbard model

. Using the multi-quasi-particle wave function based on the edge CFT, we derive the projective braid matrix for the zero modes. Finally, the connection between the non-Abelian FTSCs and the

Superconducting Proximity Effect in Topological Metal

Z_{2m}

Superconducting analogue of the parafermion fractional quantum Hall states

rotor model with a similar topological order is illustrated.