100 research outputs found
Quasiclassical theory of disordered Rashba superconductors
We derive the quasiclassical equations that describe two-dimensional
superconductors with a large Rashba spin-orbit coupling and in the presence of
impurities. These equations account for the helical phase induced by an
in-plane magnetic field, with a superconducting order parameter that is
spatially modulated along a direction perpendicular to the field. We also
derive the generalized Ginzburg-Landau functional, which includes a
linear-in-gradient term corresponding to the helical phase. This theory paves
the way for studies of the proximity effect in two-dimensional electron gases
with large spin-orbit coupling.Comment: 6 pages, 1 figur
Topological Josephson -junctions
We study the effect of a magnetic field on the current-phase relation of a
topological Josephson junction formed by connecting two superconductors through
the helical edge states of a quantum spin-Hall insulator. We predict that the
Zeeman effect along the spin quantization axis of the helical edges results in
an anomalous Josephson relation that allows for a supercurrent to flow in the
absence of superconducting phase bias. We relate the associated field-tunable
phase shift in the Josephson relation of such a -junction to
the existence of a so-called helical superconductivity, which may result from
the interplay of the Zeeman effect and spin-orbit coupling. We analyze the
dependence of the magneto-supercurrent on the junction length and discuss its
observability in suitably designed hybrid structures subject to an in-plane
magnetic field.Comment: 7 pages, 3 figures, Appendix and references adde
Non-equilibrium Josephson effect through helical edge states
We study Josephson junctions between superconductors connected through the
helical edge states of a two-dimensional topological insulator in the presence
of a magnetic barrier. As the equilibrium Andreev bound states of the junction
are 4Pi-periodic in the superconducting phase difference, it was speculated
that, at finite dc bias voltage, the junction exhibits a fractional Josephson
effect with half the Josephson frequency. Using the scattering matrix
formalism, we show that signatures of this effect can be seen in the
finite-frequency current noise. Furthermore, we discuss other manifestations of
the Majorana bound states forming at the edges of the superconductors.Comment: 4+ pages, 3 figure
Anomalous Josephson effect in semiconducting nanowires as a signature of the topologically nontrivial phase
We study Josephson junctions made of semiconducting nanowires with Rashba
spin-orbit coupling, where superconducting correlations are induced by the
proximity effect. In the presence of a suitably directed magnetic field, the
system displays the anomalous Josephson effect: a nonzero supercurrent in the
absence of a phase bias between two superconductors. We show that this
anomalous current can be increased significantly by tuning the nanowire into
the helical regime. In particular, in a short junction, a large anomalous
current is a signature for topologically nontrivial superconductivity in the
nanowire.Comment: 10 pages, 9 figures; published versio
Interplay of magneto-elastic and polaronic effects in electronic transport through suspended carbon-nanotube quantum dots
We investigate the electronic transport through a suspended carbon-nanotube
quantum dot. In the presence of a magnetic field perpendicular to the nanotube
and a nearby metallic gate, two forces act on the electrons: the Laplace and
the electrostatic force. They both induce coupling between the electrons and
the mechanical transverse oscillation modes. We find that the difference
between the two mechanisms appears in the cotunneling current
How many quasiparticles can be in a superconductor?
Experimentally and mysteriously, the concentration of quasiparticles in a
gapped superconductor at low temperatures always by far exceeds its equilibrium
value. We study the dynamics of localized quasiparticles in superconductors
with a spatially fluctuating gap edge. The competition between phonon-induced
quasiparticle recombination and generation by a weak non-equilibrium agent
results in an upper bound for the concentration that explains the mystery.Comment: 8 pages, 8 figure
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