SciPost Phys. 6, 060 (2019) ·
published 17 May 2019
|
· pdf
Among the different platforms to engineer Majorana fermions in
one-dimensional topological superconductors, topological insulator nanowires
remain a promising option. Threading an odd number of flux quanta through these
wires induces an odd number of surface channels, which can then be gapped with
proximity induced pairing. Because of the flux and depending on energetics, the
phase of this surface pairing may or may not wind around the wire in the form
of a vortex. Here we show that for wires with discrete rotational symmetry,
this vortex is necessary to produce a fully gapped topological superconductor
with localized Majorana end states. Without a vortex the proximitized wire
remains gapless, and it is only if the symmetry is broken by disorder that a
gap develops, which is much smaller than the one obtained with a vortex. These
results are explained with the help of a continuum model and validated
numerically with a tight binding model, and highlight the benefit of a vortex
for reliable use of Majorana fermions in this platform.
Henrik Schou Røising, Roni Ilan, Tobias Meng, Steven H. Simon, Felix Flicker
SciPost Phys. 6, 055 (2019) ·
published 8 May 2019
|
· pdf
We study Majorana fermions bound to vortex cores in a chiral $p$-wave
superconductor at temperatures non-negligible compared to the superconducting
gap. Thermal occupation of Caroli de Gennes-Matricon states, below the full
gap, causes the free energy difference between the two fermionic parity sectors
to decay algebraically with increasing temperature. The power law acquires an
additional factor of $T^{-1}$ for each bound state thermally excited. The
zero-temperature result is exponentially recovered well below the minigap
(lowest-lying CdGM level). Our results suggest that temperatures larger than
the minigap may not be disastrous for topological quantum computation. We
discuss the prospect of precision measurements of pinning forces on vortices as
a readout scheme for Majorana qubits.
