2,085 research outputs found
Shiba impurity bound states as a probe of topological superconductivity and Fermion parity changing quantum phase transitions
Spin-orbit coupled superconductors are potentially interesting candidates for
realizing topological and potentially non-Abelian states with Majorana
Fermions. We argue that time-reversal broken spin-orbit coupled superconductors
generically can be characterized as having sub-gap states that are bound to
localized non-magnetic impurities. Such bound states, which are referred to as
Shiba states, can be detected as sharp resonances in the tunneling spectrum of
the spin-orbit coupled superconductors. The Shiba state resonance can be tuned
using a gate-voltage or a magnetic field from being at the edge of the gap at
zero magnetic fields to crossing zero energy when the Zeeman splitting is tuned
into the topological superconducting regime. The zero-crossing signifies a
Fermion parity changing first order quantum phase transition, which is
characterized by a Pfaffian topological invariant.
These zero-crossings of the impurity level can be used to locally
characterize the topological superconducting state from tunneling experiments.Comment: 5 pages; 3 figures: minor reference update
Diamagnetic susceptibility obtained from the six-vertex model and its implications for the high-temperature diamagnetic state of cuprate superconductors
We study the diamagnetism of the 6-vertex model with the arrows as directed
bond currents. To our knowledge, this is the first study of the diamagnetism of
this model. A special version of this model, called F model, describes the
thermal disordering transition of an orbital antiferromagnet, known as
d-density wave (DDW), a proposed state for the pseudogap phase of the high-Tc
cuprates. We find that the F model is strongly diamagnetic and the
susceptibility may diverge in the high temperature critical phase with power
law arrow correlations. These results may explain the surprising recent
observation of a diverging low-field diamagnetic susceptibility seen in some
optimally doped cuprates within the DDW model of the pseudogap phase.Comment: 4.5 pages, 2 figures, revised version accepted in Phys. Rev. Let
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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