42,537 research outputs found
Wormhole Effect in a Strong Topological Insulator
An infinitely thin solenoid carrying magnetic flux Phi (a `Dirac string')
inserted into an ordinary band insulator has no significant effect on the
spectrum of electrons. In a strong topological insulator, remarkably, such a
solenoid carries protected gapless one-dimensional fermionic modes when
Phi=hc/2e. These modes are spin-filtered and represent a distinct bulk
manifestation of the topologically non-trivial insulator. We establish this
`wormhole' effect by both general qualitative considerations and by numerical
calculations within a minimal lattice model. We also discuss the possibility of
experimental observation of a closely related effect in artificially engineered
nanostructures.Comment: 4 pages, 3 figures. For related work and info visit
http://www.physics.ubc.ca/~fran
Weyl Semimetal in a Topological Insulator Multilayer
We propose a simple realization of the three-dimensional (3D) Weyl semimetal
phase, utilizing a multilayer structure, composed of identical thin films of a
magnetically-doped 3D topological insulator (TI), separated by
ordinary-insulator spacer layers. We show that the phase diagram of this system
contains a Weyl semimetal phase of the simplest possible kind, with only two
Dirac nodes of opposite chirality, separated in momentum space, in its
bandstructure. This particular type of Weyl semimetal has a finite anomalous
Hall conductivity, chiral edge states, and occurs as an intermediate phase
between an ordinary insulator and a 3D quantum anomalous Hall insulator with a
quantized Hall conductivity, equal to per TI layer. We find that the
Weyl semimetal has a nonzero DC conductivity at zero temperature and is thus an
unusual metallic phase, characterized by a finite anomalous Hall conductivity
and topologically-protected edge states.Comment: 4 pages, 3 figures, published versio
Weyl superconductors
We study the physics of the superconducting variant of Weyl semimetals, which
may be realized in multilayer structures comprising topological insulators and
superconductors. We show how superconductivity can split each Weyl node into
two. The resulting Bogoliubov Weyl nodes can be pairwise independently
controlled, allowing to access a set of phases characterized by different
numbers of bulk Bogoliubov Weyl nodes and chiral Majorana surface modes. We
analyze the physics of vortices in such systems, which trap zero energy
Majorana modes only under certain conditions. We finally comment on possible
experimental probes, thereby also exploiting the similarities between Weyl
superconductors and 2-dimensional p + ip superconductors.Comment: 13 pages, 5 figure
Strain Modulated Electronic Properties of Ge Nanowires - A First Principles Study
We used density-functional theory based first principles simulations to study
the effects of uniaxial strain and quantum confinement on the electronic
properties of germanium nanowires along the [110] direction, such as the energy
gap and the effective masses of the electron and hole. The diameters of the
nanowires being studied are up to 50 {\AA}. As shown in our calculations, the
Ge [110] nanowires possess a direct band gap, in contrast to the nature of an
indirect band gap in bulk. We discovered that the band gap and the effective
masses of charge carries can be modulated by applying uniaxial strain to the
nanowires. These strain modulations are size-dependent. For a smaller wire (~
12 {\AA}), the band gap is almost a linear function of strain; compressive
strain increases the gap while tensile strain reduces the gap. For a larger
wire (20 {\AA} - 50 {\AA}), the variation of the band gap with respect to
strain shows nearly parabolic behavior: compressive strain beyond -1% also
reduces the gap. In addition, our studies showed that strain affects effective
masses of the electron and hole very differently. The effective mass of the
hole increases with a tensile strain while the effective mass of the electron
increases with a compressive strain. Our results suggested both strain and size
can be used to tune the band structures of nanowires, which may help in design
of future nano-electronic devices. We also discussed our results by applying
the tight-binding model.Comment: 1 table, 8 figure
Spin and Charge Structure of the Surface States in Topological Insulators
We investigate the spin and charge densities of surface states of the
three-dimensional topological insulator , starting from the continuum
description of the material [Zhang {\em et al.}, Nat. Phys. 5, 438 (2009)]. The
spin structure on surfaces other than the 111 surface has additional complexity
because of a misalignment of the contributions coming from the two sublattices
of the crystal. For these surfaces we expect new features to be seen in the
spin-resolved ARPES experiments, caused by a non-helical spin-polarization of
electrons at the individual sublattices as well as by the interference of the
electron waves emitted coherently from two sublattices. We also show that the
position of the Dirac crossing in spectrum of surface states depends on the
orientation of the interface. This leads to contact potentials and surface
charge redistribution at edges between different facets of the crystal.Comment: Use the correct spin operator. Changes affect the surface states spin
structure, but not the spectru
Inf-convolution of G-expectations
In this paper we will discuss the optimal risk transfer problems when risk
measures are generated by G-expectations, and we present the relationship
between inf-convolution of G-expectations and the inf-convolution of drivers G.Comment: 23 page
In-medium Properties of as a KN structure in Relativistic Mean Field Theory
The properties of nuclear matter are discussed with the relativistic
mean-field theory (RMF).Then, we use two models in studying the in-medium
properties of : one is the point-like in the usual RMF and
the other is a KN structure for the pentaquark. It is found that the
in-medium properties of are dramatically modified by its internal
structure. The effective mass of in medium is, at normal nuclear
density, about 1030 MeV in the point-like model, while it is about 1120 MeV in
the model of KN pentaquark. The nuclear potential depth of in
the KN model is approximately -37.5 MeV, much shallower than -90 MeV in
the usual point-like RMF model.Comment: 8 pages, 5 figure
Erratum : Squeezing and entanglement delay using slow light
An inconsistency was found in the equations used to calculate the variance of
the quadrature fluctuations of a field propagating through a medium
demonstrating electromagnetically induced transparency (EIT). The decoherence
term used in our original paper introduces inconsistency under weak probe
approximation. In this erratum we give the Bloch equations with the correct
dephasing terms. The conclusions of the original paper remain the same. Both
entanglement and squeezing can be delayed and preserved using EIT without
adding noise when the decoherence rate is small.Comment: 1 page, no figur
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