Publications (7)30.27 Total impact
 [Show abstract] [Hide abstract]
ABSTRACT: It is generally thought that adiabatic exchange of two identical particles is impossible in one spatial dimension. Here we describe a simple protocol that permits adiabatic exchange of two Majorana fermions in a onedimensional topological superconductor wire. The exchange relies on the concept of ``Majorana shuttle'' whereby a $\pi$ domain wall in the superconducting order parameter which hosts a pair of ancillary Majoranas delivers one zero mode across the wire while the other one tunnels in the opposite direction. The method requires some tuning of parameters and does not, therefore, enjoy the full topological protection. The resulting exchange statistics, however, remains nonAbelian for a wide range of parameters that characterize the exchange.  [Show abstract] [Hide abstract]
ABSTRACT: Most physical systems known to date tend to resist entering the topological phase and must be finetuned to reach that phase. Here, we introduce a system in which a key dynamical parameter adjusts itself in response to the changing external conditions so that the ground state naturally favors the topological phase. The system consists of a quantum wire formed of individual magnetic atoms placed on the surface of an ordinary swave superconductor. It realizes the Kitaev paradigm of topological superconductivity when the wave vector characterizing the emergent spin helix dynamically selftunes to support the topological phase. We call this phenomenon a selforganized topological state.  [Show abstract] [Hide abstract]
ABSTRACT: It has been suggested recently, based on subtle fieldtheoretical considerations, that the electromagnetic response of Weyl semimetals and the closely related Weyl insulators can be characterized by an axion term θE·B with space and time dependent axion angle θ(r,t). Here we construct a minimal lattice model of the Weyl medium and study its electromagnetic response by a combination of analytical and numerical techniques. We confirm the existence of the anomalous Hall effect expected on the basis of the field theory treatment. We find, contrary to the latter, that chiral magnetic effect (that is, ground state charge current induced by the applied magnetic field) is absent in both the semimetal and the insulator phase. We elucidate the reasons for this discrepancy.  [Show abstract] [Hide abstract]
ABSTRACT: We show that isolated Weyl nodes can arise in a system of parallel topological insulator nanowires arranged in a honeycomb fashion. This introduces another theoretical example of a topological semimetal phase with more than one pair of Weyl nodes and due to the simple form of its Hamiltonian it can be used to study various interesting phenomena associated with this phase. Our result emphasizes that depending on the separation of the Weyl nodes a topological electromagnetic response might or might not emerge and two pairs might have overall cancelling contributions to the net anomalous Hall conductivity.  [Show abstract] [Hide abstract]
ABSTRACT: It has been shown previously that a finitelength topological insulator nanowire, proximitycoupled to an ordinary bulk swave superconductor and subject to a longitudinal applied magnetic field, realizes a onedimensional topological superconductor with an unpaired Majorana fermion (MF) localized at each end of the nanowire. Here, we study the stability of these MFs with respect to various perturbations that are likely to occur in a physical realization of the proposed device. We show that the unpaired Majorana fermions persist in this system for any value of the chemical potential inside the bulk band gap of order 300 meV in Bi$_2$Se$_3$ by computing the Majorana number. From this calculation, we also show that the unpaired Majorana fermions persist when the magnetic flux through the nanowire crosssection deviates significantly from half flux quantum. Lastly, we demonstrate that the unpaired Majorana fermions persist in strongly disordered wires with fluctuations in the onsite potential ranging in magnitude up to several times the size of the bulk band gap. These results suggest this solidstate system should exhibit unpaired Majorana fermions under accessible conditions likely important for experimental study or future applications.  [Show abstract] [Hide abstract]
ABSTRACT: The surface of a topological insulator hosts a very special form of a quasitwo dimensional metallic system when it is embedded in a topologically trivial medium like the vacuum. The electronic properties of this unusual 2D metal are distinct in many aspects from both the conventional twodimensional electron gas systems in quantum well heterostructures as well as those of a single layer graphene. In this paper, we study one of these distinct features i.e., the response of the electronic spins to an applied magnetic field perpendicular to the surface. We find an unusual behaviour of the spin magnetization and susceptibility as a function of both the magnetic field and the chemical potential for a generic topological surface. We propose that this behavior could be studied by the recently developed experimental technique called \beta NMR which is highly sensitive to the surface electron spins. We explain how this technique could be used to probe for spontaneous magnetic ordering caused by magnetic dopants or interactions discussed in the recent literature.  [Show abstract] [Hide abstract]
ABSTRACT: The Lagrangian describing the bulk electromagnetic response of a threedimensional strong topological insulator contains a topological `axion' term of the form '\theta E dot B'. It is often stated (without proof) that the corresponding action is quantized on periodic spacetime and therefore invariant under '\theta > \theta +2\pi'. Here we provide a simple, physically motivated proof of the axion action quantization on the periodic spacetime, assuming only that the vector potential is consistent with singlevaluedness of the electron wavefunctions in the underlying insulator.
Publication Stats
166  Citations  
30.27  Total Impact Points  
Top Journals
Institutions

20102013

University of British Columbia  Vancouver
 Department of Physics and Astronomy
Vancouver, British Columbia, Canada
