828 research outputs found
`Unhinging' the surfaces of higher-order topological insulators and superconductors
We show that the chiral Dirac and Majorana hinge modes in three-dimensional
higher-order topological insulators (HOTIs) and superconductors (HOTSCs) can be
gapped while preserving the protecting symmetry
upon the introduction of non-Abelian surface topological order. In both cases,
the topological order on a single side surface breaks time reversal symmetry,
but appears with its time-reversal conjugate on alternating sides in a
preserving pattern. In the absence of the
HOTI/HOTSC bulk, such a pattern necessarily involves gapless chiral modes on
hinges between -conjugate domains. However, using a
combination of -matrix and anyon condensation arguments, we show that on the
boundary of a 3D HOTI/HOTSC these topological orders are fully gapped and hence
`anomalous'. Our results suggest that new patterns of surface and hinge states
can be engineered by selectively introducing topological order only on specific
surfaces
Incorporation of amino acids into the outer and inner membrane of isolated rat liver mitochondria II
Carbon coating of the SPS dipole chambers
The Electron Multipacting (EM) phenomenon is a limiting factor for the
achievement of high luminosity in accelerators for positively charged particles
and for the performance of RF devices. At CERN, the Super Proton Synchrotron
(SPS) must be upgraded in order to feed the Large Hadron Collider (LHC) with 25
ns bunch spaced beams. At such small bunch spacing, EM may limit the
performance of the SPS and consequently that of the LHC. To mitigate this
phenomenon CERN is developing a carbon thin film coating with low Secondary
Electron Yield (SEY) to coat the internal walls of the SPS dipoles beam pipes.
This paper presents the progresses in the coating technology, the performance
of the carbon coatings and the strategy for a large scale production.Comment: 7 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Italy; CERN Yellow Report CERN-2013-002, pp.141-14
Higher-Order Topological Insulators
Three-dimensional topological (crystalline) insulators are materials with an
insulating bulk, but conducting surface states which are topologically
protected by time-reversal (or spatial) symmetries. Here, we extend the notion
of three-dimensional topological insulators to systems that host no gapless
surface states, but exhibit topologically protected gapless hinge states. Their
topological character is protected by spatio-temporal symmetries, of which we
present two cases: (1) Chiral higher-order topological insulators protected by
the combination of time-reversal and a four-fold rotation symmetry. Their hinge
states are chiral modes and the bulk topology is -classified. (2)
Helical higher-order topological insulators protected by time-reversal and
mirror symmetries. Their hinge states come in Kramers pairs and the bulk
topology is -classified. We provide the topological invariants for
both cases. Furthermore we show that SnTe as well as surface-modified
BiTeI, BiSe, and BiTe are helical higher-order topological insulators and
propose a realistic experimental setup to detect the hinge states.Comment: 8 pages (4 figures) and 16 pages supplemental material (7 figures
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