5,842 research outputs found
Near-zero-energy end states in topologically trivial spin-orbit coupled superconducting nanowires with a smooth confinement
A one-dimensional spin-orbit coupled nanowire with proximity-induced pairing
from a nearby s-wave superconductor may be in a topological nontrivial state,
in which it has a zero energy Majorana bound state at each end. We find that
the topological trivial phase may have fermionic end states with an
exponentially small energy, if the confinement potential at the wire's ends is
smooth. The possible existence of such near-zero energy levels implies that the
mere observation of a zero-bias peak in the tunneling conductance is not an
exclusive signature of a topological superconducting phase even in the ideal
clean single channel limit.Comment: 4 pages, 4 figure
Finite size effects and localization properties of disordered quantum wires with chiral symmetry
Finite size effects in the localization properties of disordered quantum
wires are analyzed through conductance calculations. Disorder is induced by
introducing vacancies at random positions in the wire and thus preserving the
chiral symmetry. For quasi one-dimensional geometries and low concentration of
vacancies, an exponential decay of the mean conductance with the wire length is
obtained even at the center of the energy band. For wide wires, finite size
effects cause the conductance to decay following a non-pure exponential law. We
propose an analytical formula for the mean conductance that reproduces
accurately the numerical data for both geometries. However, when the
concentration of vacancies increases above a critical value, a transition
towards the suppression of the conductance occurs.
This is a signature of the presence of ultra-localized states trapped in
finite regions of the sample.Comment: 5 figures, revtex
Crossover from weak localization to weak antilocalization in a disordered microbridge
We calculate the weak localization correction in the double crossover to
broken time-reversal and spin-rotational symmetry for a disordered microbridge
or a short disordered wire using a scattering-matrix approach. Whereas the
correction has universal limiting values in the three basic symmetry classes,
the functional form of the magnetoconductance is affected by eventual
non-homogeneities in the microbridge.Comment: 5 pages, RevTeX; 2 figure
Weak Coulomb blockade effect in quantum dots
We develop the general non-equilibrium theory of transport through a quantum
dot, including Coulomb Blockade effects via a 1/N expansion, where N is the
number of scattering channels. At lowest order we recover the Landauer formula
for the current plus a self-consistent equation for the dot potential. We
obtain the leading corrections and compare with earlier approaches. Finally, we
show that to leading and next leading order in 1/N there is no interaction
correction to the weak localization, in contrast to previous theories, but
consistent with experiments by Huibers et al. [Phys. Rev. Lett. 81, 1917
(1998)], where N=4.Comment: 4 pages, 2 figures. Published versio
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
Endstates in multichannel spinless p-wave superconducting wires
Multimode spinless p-wave superconducting wires with a width W much smaller
than the superconducting coherence length \xi are known to have multiple
low-energy subgap states localized near the wire's ends. Here we compare the
typical energies of such endstates for various terminations of the wire: A
superconducting wire coupled to a normal-metal stub, a weakly disordered
superconductor wire and a wire with smooth confinement. Depending on the
termination, we find that the energies of the subgap states can be higher or
lower than for the case of a rectangular wire with hard-wall boundaries.Comment: 10 pages, 7 figure
Centerlines of regions in the sphere
AbstractGiven a region U in the 2-sphere S such that the boundary of U contains at least two points, let D(U) be the collection of open circular disks (called maximal disks) in U whose boundary meets the boundary of U in at least two points and let U2 be the collection of all regions U⊂S such that for each D∈D(U), D meets the boundary of U in at most two points. In this paper we study geometric properties of regions U∈U2. We show for such U that the centerline (i.e., the set of centers of maximal disks) is always a smooth, connected 1-manifold. We also show that the boundary of U has at most two components and, if it has exactly two components, then the boundary is locally connected.These results are related the set of points E(X,Y) which are equidistant to two disjoint closed sets X and Y. In particular we investigate when the equidistant set is a 1-manifold
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