3,505 research outputs found
Tri-Dirac Surface Modes in Topological Superconductors
We propose a new type of topological surface modes having cubic dispersion in
three-dimensional topological superconductors. Lower order dispersions are
prohibited by the threefold rotational symmetry and time-reversal symmetry.
Cooper pairing in the bulk changes sign under improper rotations, akin
toHe-B. The surface manifestations are a divergent surface density of
states at the Fermi level and isospins that rotate three times as they circle
the origin in momentum space. We propose that Heusler alloys with band
inversion are candidate materials to harbor the novel topological
superconductivity.Comment: Five-page main text plus five-page supplementary materials; three
figure
Entanglement Spectrum Classification of -invariant Noninteracting Topological Insulators in Two Dimensions
We study the single particle entanglement spectrum in 2D topological
insulators which possess -fold rotation symmetry. By defining a series of
special choices of subsystems on which the entanglement is calculated, or real
space cuts, we find that the number of protected in-gap states for each type of
these real space cuts is a quantum number indexing (if any) non-trivial
topology in these insulators. We explicitly show the number of protected in-gap
states is determined by a -index, , where is the
number of occupied states that transform according to -th one-dimensional
representation of the point group. We find that the entanglement spectrum
contains in-gap states pinned in an interval of entanglement eigenvalues
. We determine the number of such in-gap states for an exhaustive
variety of cuts, in terms of the quantum numbers. Furthermore, we show
that in a homogeneous system, the index can be determined through an
evaluation of the eigenvalues of point group symmetry operators at all
high-symmetry points in the Brillouin zone. When disordered -fold
rotationally symmetric systems are considered, we find that the number of
protected in-gap states is identical to that in the clean limit as long as the
disorder preserves the underlying point group symmetry and does not close the
bulk insulating gap.Comment: 14.2 pages for main text, 4.8 pages for Appendices, four figures and
two table
Large Chern Number Quantum Anomalous Hall Effect In Thin-film Topological Crystalline Insulators
Quantum anomalous Hall (QAH) insulators are two-dimensional (2D) insulating
states exhibiting properties similar to those of quantum Hall states but
without external magnetic field. They have quantized Hall conductance
, where integer is called the Chern number, and represents
the number of gapless edge modes. Recent experiments demonstrated that chromium
doped thin-film (Bi,Sb)Te is a QAH insulator with Chern number
. Here we theoretically predict that thin-film topological crystalline
insulators (TCI) can host various QAH phases, when doped by ferromagnetically
ordered dopants. Any Chern number between can, in principle, be reached
as a result of the interplay between (a) the induced Zeeman field, depending on
the magnetic doping concentration, (b) the structural distortion, either
intrinsic or induced by a piezoelectric material through proximity effect and
(c) the thickness of the thin film. The tunable Chern numbers found in TCI
possess significant potential for ultra-low power information processing
applications.Comment: References update
New class of topological superconductors protected by magnetic group symmetries
We study a new type of three-dimensional topological superconductors that
exhibit Majorana zero modes (MZM) protected by a magnetic group symmetry, a
combined antiunitary symmetry composed of a mirror reflection and
time-reversal. This new symmetry enhances the noninteracting topological
classification of a superconducting vortex from to , indicating that
multiple MZMs can coexist at the end of one magnetic vortex of unit flux.
Specially, we show that a vortex binding two MZMs can be realized on the
-surface of a topological crystalline insulator SnTe with proximity
induced BCS Cooper pairing, or in bulk superconductor InSnTe.Comment: Accepted version to appear in PRL: 4-page text plus 4-page
supplementary materials, two figure
Electronic transport in a two-dimensional superlattice engineered via self-assembled nanostructures
Nanoscience offers a unique opportunity to design modern materials from the
bottom up, via low-cost, solution processed assembly of nanoscale building
blocks. These systems promise electronic band structure engineering using not
only the nanoscale structural modulation, but also the mesoscale spatial
patterning, although experimental realization of the latter has been
challenging. Here we design and fabricate a new type of artificial solid by
stacking graphene on a self-assembled, nearly periodic array of nanospheres,
and experimentally observe superlattice miniband effects. We find conductance
dips at commensurate fillings of charge carriers per superlattice unit cell,
which are key features of minibands that are induced by the quasi-periodic
deformation of the graphene lattice. These dips become stronger when the
lattice strain is larger. Using a tight-binding model, we simulate the effect
of lattice deformation as a parameter affecting the inter-atomic hopping
integral, and confirm the superlattice transport behavior. This 2D
material-nanoparticle heterostructure enables facile band structure engineering
via self-assembly, promising for large area electronics and optoelectronics
applications
- …