31 research outputs found
Supercurrent as a Probe for Topological Superconductivity in Magnetic Adatom Chains
A magnetic adatom chain, proximity coupled to a conventional superconductor
with spin-orbit coupling, exhibits locally an odd-parity, spin-triplet pairing
amplitude. We show that the singlet-triplet junction, thus formed, leads to a
net spin accumulation in the near vicinity of the chain. The accumulated spins
are polarized along the direction of the local -vector for triplet
pairing and generate an enhanced persistent current flowing around the chain.
The spin polarization and the "supercurrent" reverse their directions beyond a
critical exchange coupling strength at which the singlet superconducting order
changes its sign on the chain. The current is strongly enhanced in the
topological superconducting regime where Majorana bound states appear at the
chain ends. The current and the spin profile offer alternative routes to
characterize the topological superconducting state in adatom chains and
islands.Comment: 5 pages, 3 figures, 5 pages of supplemental material
Supercurrent and phase signatures of topological superconductivity in planar Josephson junctions
We consider planar Josephson junctions, with dimensions as used in recent
experiments, and show using numerical calculations that the junctions undergo
topological superconducting transition, revealed by the appearance of
zero-energy Majorana bound states at the ends of the non-superconducting
channel of the junctions in the presence of an in-plane magnetic field and
phase difference between the superconducting leads. Our main finding is
that, under realistic parameter settings, the critical supercurrent undergoes a
minimum and the ground state phase increases from zero toward at a
critical field, without the junctions necessarily transitioning into a
topological superconducting phase. Remarkably, the critical supercurrent
minimum and a simultaneous sharp jump in the ground state phase appear in
junctions that are undoubtedly in trivial superconducting phase. Our results
provide updated insights for experimental detection of topological
superconductivity in planar Josephson junctions using the supercurrent and
phase signatures.Comment: Comments are welcom
Skyrmion Control of Majorana States in Planar Josephson Junctions
Planar Josephson junctions provide a versatile platform, alternative to the
nanowire-based geometry, for the generation of the Majorana bound states, due
to the additional phase tunability of the topological superconductivity. The
proximity induction of chiral magnetism and superconductivity in a
two-dimensional electron gas showed remarkable promises to manipulate
topological superconductivity. Here, we consider a Josephson junction involving
a skyrmion crystal and show that the chiral magnetism of the skyrmions can
create and control the Majorana bound states without the requirement of an
intrinsic Rashba spin-orbit coupling. Interestingly, the Majorana bound states
in our geometry are realized robustly at zero phase difference at the junction.
The skyrmion radius, being externally tunable by a magnetic field or a magnetic
anisotropy, brings a unique control feature for the Majorana bound states
Majorana fusion in interacting one-dimensional Kitaev chains
We employ a time-dependent real-space local density-of-states method to study
the movement and fusion of Majorana zero modes in the 1D interacting Kitaev
model, based on the time evolution of many-body states. We study the dynamics
and both fusion channels of Majoranas using time-dependent potentials, either
{\it Wall} or {\it Well}, focusing on the local density-of-states and
charge-density of fermions varying with time. For a {\it Wall}, i.e. repulsive
strong potential, after fusion of Majoranas the electron (or hole) forms at
, whereas for a {\it Well}, i.e. attractive deep potential, electron
(or hole) forms at , where is the Coulomb repulsion. We
also describe specific upper and lower limits on the Majorana movement needed
to reduce non-adiabatic effects as well as to avoid poisoning due to
decoherence, focusing on forming a full electron (or hole) after the fusion.Comment: 5 figure
In-gap features in superconducting LaAlO-SrTiO interfaces observed by tunneling spectroscopy
We identified quasiparticle states at well-defined energies inside the
superconducting gap of the electron system at the LaAlO-SrTiO interface
using tunneling spectroscopy. The states are found only in a number of samples
and depend upon the thermal-cycling history of the samples. The states consist
of a peak at zero energy and other peaks at finite energies, symmetrically
placed around zero energy. These peaks disappear, together with the
superconducting gap, with increasing temperature and magnetic field. We discuss
the likelihood of various physical mechanisms that are known to cause in-gap
states in superconductors and conclude that none of these mechanisms can easily
explain the results. The conceivable scenarios are the formation of Majorana
bound states, Andreev bound states, or the presence of an odd-frequency spin
triplet component in the superconducting order parameter.Comment: 11 pages, 5 figure