1,945 research outputs found
Conductance oscillations and speed of chiral Majorana mode in a quantum-anomalous-Hall 2d strip
We predict conductance oscillations in a quantum-anomalous Hall 2d strip
having a superconducting region of length with a chiral Majorana mode.
These oscillations require a finite transverse extension of the strip of
a few microns or less. Measuring the conductance periodicity with and a
fixed bias, or with bias and a fixed , yields the speed of the chiral
Majorana mode. The physical mechanism behind the oscillations is the
interference between backscattered chiral modes from second to first interface
of the NSN double junction. The interferometer effect is enhanced by the
presence of side barriers.Comment: 9 pages, 9 figures. Added references. Added Supplemental Material
results. Published versio
Topological suppression of magnetoconductance oscillations in NS junctions
We show that the magnetoconductance oscillations of laterally-confined 2D NS
junctions are completely suppressed when the superconductor side enters a
topological phase. This suppression can be attributed to the modification of
the vortex structure of local currents at the junction caused by the
topological transition of the superconductor. The two regimes (with and without
oscillations) could be seen in a semiconductor 2D junction with a cleaved-edge
geometry, one of the junction arms having proximitized superconductivity. We
predict similar oscillations and suppression as a function of the Rashba
coupling. The oscillation suppression is robust against differences in chemical
potential and phases of lateral superconductors.Comment: 7 pages, 7 figure
Majorana states and magnetic orbital motion in planar hybrid nanowires
The Majorana phase boundaries in planar 2D hybrid
(semiconductor-superconductor) nanowires are modified by orbital effects due to
off plane magnetic components. We show that Majorana zero modes survive sizable
vertical field tiltings, uncovering a remarkable phase diagram. Analytical
expressions of the phase boundaries are given for the strong orbital limit.
These phase boundaries can be fulfilled with attainable setups, such as an InAs
nanowire of in transverse width.Comment: 9 pages, 6 figures. ( Only acknowledgement update
Electromagnetic absorption of quasi-1D Majorana nanowires
We calculate the electromagnetic absorption cross section of long and narrow
nanowires, in the so-called quasi-1D limit. We consider only two transverse
bands and compute the dipole absorption cross section taking into account
quasiparticle transitions from negative to positive energy eigenstates of the
Bogoliubov-de Gennes Hamiltonian. The presence of the zero energy (Majorana)
state manifests in the different absorption spectra for (parallel) and
(transverse) polarizations of the electromagnetic field.
In the -polarized case, the Majorana state causes a low energy absorption
plateau extending from mid-gap up to full-gap energy. Increasing further the
energy, the plateau is followed by a region of enhanced absorption due to
transitions across the full gap. For polarization the low energy absorption
plateau is not observed.Comment: Submitted to E-MRS Spring Meeting 2015 ( Only acknowledgement update
Effects of tilting the magnetic field in 1D Majorana nanowires
We investigate the effects that a tilting of the magnetic field from the
parallel direction has on the states of a 1D Majorana nanowire. Particularly,
we focus on the conditions for the existence of Majorana zero modes, uncovering
an analytical relation (the sine rule) between the field orientation relative
to the wire, its magnitude and the superconducting parameter of the material.
The study is then extended to junctions of nanowires, treated as magnetically
inhomogeneous straight nanowires composed of two homogeneous arms. It is shown
that their spectrum can be explained in terms of the spectra of two independent
arms. Finally, we investigate how the localization of the Majorana mode is
transferred from the magnetic interface at the corner of the junction to the
end of the nanowire when increasing the arm length.Comment: 10 pages, 13 figures. ( Only acknowledgement update
Zoning and the Law of Nuisance
We calculate density and current spatial distributions of a 2D model junction between a normal QAH contact and a superconducting QAH region hosting propagating (chiral) Majorana modes. We use a simplified Hamiltonian describing the spatial coupling of the modes on each side of the junction, as well as the related junction conductance. We study how this coupling is affected by orbital effects caused by an external magnetic field.This work was funded by MINEICO-Spain, grant MAT2017-82639
Sidon set systems
A family of -subsets of is a Sidon
system if the sumsets , are pairwise distinct. We
show that the largest cardinality of a Sidon system of -subsets of
satisfies and the asymptotic lower bound
. More precise bounds on are obtained for
. We also obtain the threshold probability for a random system to be
Sidon for .Comment: Incorporated referee comments. Published in Rev. Mat. Iberoa
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