1,321 research outputs found
Edge instabilities of topological superconductors
Nodal topological superconductors display zero-energy Majorana flat bands at
generic edges. The flatness of these edge bands, which is protected by
time-reversal and translation symmetry, gives rise to an extensive ground-state
degeneracy. Therefore, even arbitrarily weak interactions lead to an
instability of the flat-band edge states towards time-reversal and
translation-symmetry-broken phases, which lift the ground-state degeneracy. We
examine the instabilities of the flat-band edge states of d_{xy}-wave
superconductors by performing a mean-field analysis in the Majorana basis of
the edge states. The leading instabilities are Majorana mass terms, which
correspond to coherent superpositions of particle-particle and particle-hole
channels in the fermionic language. We find that attractive interactions induce
three different mass terms. One is a coherent superposition of imaginary s-wave
pairing and current order, and another combines a charge-density-wave and
finite-momentum singlet pairing. Repulsive interactions, on the other hand,
lead to ferromagnetism together with spin-triplet pairing at the edge. Our
quantum Monte Carlo simulations confirm these findings and demonstrate that
these instabilities occur even in the presence of strong quantum fluctuations.
We discuss the implications of our results for experiments on cuprate
high-temperature superconductors.Comment: 4 pages, 3 figure
Long-Wavelength Anomalies in the Asymptotic Behavior of Mode-Coupling Theory
We discuss the dynamic behavior of a tagged particle close to a classical
localization transition in the framework of the mode-coupling theory of the
glass transition. Asymptotic results are derived for the order parameter as
well as the dynamic correlation functions and the mean-squared displacement
close to the transition. The influence of an infrared cutoff is discussed.Comment: 15 pages, 8 figures, to appear in J Phys Condens Matte
Fermion zero modes at the boundary of superfluid 3He-B
Superfluid 3He-B belongs to the important special class of time-reversal
invariant topological superfluids. It has Majorana fermions as edge states on
the surface of bulk 3He-B. On the rough wall these fermion zero modes have
finite density of states at E=0. It is possible that Lancaster experiments with
a wire vibrating in 3He-B have already probed Majorana fermions living on the
surface of the wire.Comment: 4 pages, no Figures, JETP Letters style, version to be published in
JETP Letter
Evolution of edge states in topological superfluids during the quantum phase transition
The quantum phase transition between topological and non-topological
insulators or between fully gapped superfluids/superconductors can occur
without closing the gap. We consider the evolution of the Majorana edge states
on the surface of topological superconductor during transition to the
topologically trivial superconductor on example of non-interacting Hamiltonian
describing the spin-triplet superfluid 3He-B. In conventional situation when
the gap is nullified at the transition, the spectrum of Majorana fermions
shrinks and vanishes after the transition to the trivial state. If the
topological transition occurs without the gap closing, the Majorana fermion
spectrum disappears by escaping to ultraviolet, where Green's function
approaches zero. This demonstrates the close connection between the topological
transition without closing the gap and zeroes in the Green's function. Similar
connection takes place in interacting systems where zeroes may occur due to
interaction.Comment: 5 pages, 2 figures, JETP Letters style, version submitted to JETP
Letter
Spin Berry phase in the Fermi arc states
Unusual electronic property of a Weyl semi-metallic nanowire is revealed. Its
band dispersion exhibits multiple subbands of partially flat dispersion,
originating from the Fermi arc states. Remarkably, the lowest energy flat
subbands bear a finite size energy gap, implying that electrons in the Fermi
arc surface states are susceptible of the spin Berry phase. This is shown to be
a consequence of spin-to-surface locking in the surface electronic states. We
verify this behavior and the existence of spin Berry phase in the low-energy
effective theory of Fermi arc surface states on a cylindrical nanowire by
deriving the latter from a bulk Weyl Hamiltonian. We point out that in any
surface state exhibiting a spin Berry phase pi, a zero-energy bound state is
formed along a magnetic flux tube of strength, hc/(2e). This effect is
highlighted in a surfaceless bulk system pierced by a dislocation line, which
shows a 1D chiral mode along the dislocation line.Comment: 9 pages, 9 figure
Imaging of cavitary necrosis in complicated childhood pneumonia
Abstract.: The aim of this study was to illustrate the chest radiographs (CR) and CT imaging features and sequential findings of cavitary necrosis in complicated childhood pneumonia. Among 30 children admitted in the Pediatric Intensive Care Unit for persistent or progressive pneumonia, respiratory distress or sepsis despite adequate antibiotic therapy, a study group of 9 children (5 girls and 4 boys; mean age 4years) who had the radiographic features and CT criteria for cavitary necrosis complicated pneumonia was identified. The pathogens identified were Streptococcus pneumoniae (n=4), Aspergillus (n=2), Legionella (n=1), and Staphylococcus aureus (n=1). Sequential CR and CT scans were retrospectively reviewed. Follow-up CR and CT were evaluated for persistent abnormalities. Chest radiographs showed consolidations in 8 of the 9 patients. On CT examination, cavitary necrosis was localized to 1 lobe in 2 patients and 7 patients showed multilobar or bilateral areas of cavitary necrosis. In 3 patients of 9, the cavitary necrosis was initially shown on CT and visualization by CR was delayed by a time span varying from 5 to 9days. In all patients with cavities, a mean number of five cavities were seen on antero-posterior CR, contrasting with the multiple cavities seen on CT. Parapneumonic effusions were shown by CR in 3 patients and in 5 patients by CT. Bronchopleural fistulae were demonstrated by CT alone (n=3). No purulent pericarditis was demonstrated. The CT scan displayed persistent residual pneumatoceles of the left lower lobe in 2 patients. Computed tomography is able to define a more specific pattern of abnormalities than conventional CR in children with necrotizing pneumonia and allows an earlier diagnosis of this rapidly progressing condition. Lung necrosis and cavitation may also be associated with Aspergillus or Legionella pneumonia in the pediatric populatio
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