2,814 research outputs found
Experimental and materials considerations for the topological superconducting state in electron and hole doped semiconductors: searching for non-Abelian Majorana modes in 1D nanowires and 2D heterostructures
In proximity to an s-wave superconductor, a one- or two-dimensional,
electron- or hole-doped semiconductor with a sizable spin-orbit coupling and a
Zeeman splitting can support a topological superconducting (TS) state. The
semiconductor TS state has Majorana fermions as localized zero-energy
excitations at order parameter defects such as vortices and sample edges. Here
we examine the effects of quenched disorder from the semiconductor surface on
the stability of the TS state in both electron- and hole-doped semiconductors.
By considering the interplay of broken time reversal symmetry (due to Zeeman
splitting) and disorder we derive an expression for the disorder suppression of
the superconducting quasiparticle gap in the TS state. We conclude that the
effects of disorder can be minimized by increasing the ratio of the spin-orbit
energy with the Zeeman splitting. By giving explicit numbers we show that a
stable TS state is possible in both electron- and hole-doped semiconductors for
experimentally realistic values of parameters. We discuss possible suitable
semiconductor materials which should be the leading candidates for the Majorana
search in solid state systems.Comment: 11 pages, 2 figures: v3 published versio
Antiferromagnetic Spinor Condensates are Quantum Rotors
We establish a theoretical correspondence between spin-one antiferromagnetic
spinor condensates in an external magnetic field and quantum rotor models in an
external potential. We show that the rotor model provides a conceptually clear
picture of the possible phases and dynamical regimes of the antiferromagnetic
condensate. We also show that this mapping simplifies calculations of the
condensate's spectrum and wavefunctions. We use the rotor mapping to describe
the different dynamical regimes recently observed in Na condensates. We
also suggest a way to experimentally observe quantum mechanical effects
(collapse and revival) in spinor condensates.Comment: minor revisions. some typos correcte
Integro-differential diffusion equation for continuous time random walk
In this paper we present an integro-differential diffusion equation for
continuous time random walk that is valid for a generic waiting time
probability density function. Using this equation we also study diffusion
behaviors for a couple of specific waiting time probability density functions
such as exponential, and a combination of power law and generalized
Mittag-Leffler function. We show that for the case of the exponential waiting
time probability density function a normal diffusion is generated and the
probability density function is Gaussian distribution. In the case of the
combination of a power-law and generalized Mittag-Leffler waiting probability
density function we obtain the subdiffusive behavior for all the time regions
from small to large times, and probability density function is non-Gaussian
distribution.Comment: 12 page
How to realize a robust practical Majorana chain in a quantum dot-superconductor linear array
Semiconducting nanowires in proximity to superconductors are promising
experimental systems for Majorana fermions, which may ultimately be used as
building blocks for topological quantum computers. A serious challenge in the
experimental realization of the Majorana fermions is the supression of
topological superconductivity by disorder. We show that Majorana fermions
protected by a robust topological gap can occur at the ends of a chain of
quantum dots connected by s-wave superconductors. In the appropriate parameter
regime, we establish that the quantum dot/superconductor system is equivalent
to a 1D Kitaev chain, which can be tuned to be in a robust topological phase
with Majorana end modes even in the case where the quantum dots and
superconductors are both strongly disordered. Such a spin-orbit coupled quantum
dot - s-wave superconductor array provides an ideal experimental platform for
the observation of non-Abelian Majorana modes.Comment: 8 pages; 3 figures; version 2: Supplementary material updated to
include more general proof for localized Majorana fermion
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