77 research outputs found
Three-dimensional symmetry breaking topological matters
We discuss topological electronic states described by the Dirac Hamiltonian
plus an additional one in three-dimension. When the additional Hamiltonian is
an element of an Abelian group, electronic states become topologically
nontrivial even in the absence of fundamental symmetries such as the
time-reversal and the particle-hole symmety. The symmetry-breaking topological
states are charercterized by the Chern number defined in the two-dimensional
partial Brillouin zone. The topological insulators under Zeeman field are an
example of the symmetry-breaking topological matters. We show the transision
from the topological insulating phase to the topological semimetal one under
the strong Zeeman field.Comment: 5 pages, 4 figure
Robustness of Gapless Interface State in a Junction of Two Topological Insulators
We theoretically study subgap states appearing at the interface between two
three-dimensional topological insulators which have different configurations in
the spin-orbit interactions from each other. The coupling of spin
with momenta is configured by a material
dependent matrix as . We show that the spectra of the interface suggap
states depend strongly on the relative choices of in the
two topological insulators. In particular, we focus on properties of gapless
states which appear when in two topological insulators
are connected by the inversion in momentum space. We also discuss the
robustness of the gapless states under perturbations breaking the time-reversal
symmetry or the band-inversion symmetry by the numerical simulation.Comment: 13 pages, 9 figure
Interface Metallic States between a Topological Insulator and a Ferromagnetic Insulator
We study electronic structures at an interface between a topological
insulator and a ferromagnetic insulator by using three-dimensional two-band
model. In usual ferromagnetic insulators, the exchange potential is much larger
than the bulk gap size in the topological insulators and electronic structures
are asymmetric with respect to the fermi level. In such situation, we show that
unusual metallic states appear under the magnetic moment pointing the
perpendicular direction to the junction plane, which cannot be described by the
two-dimensional effective model around the Dirac point.
When the magnetic moment is in the parallel direction to the plane, the
number of Dirac cones becomes even integers. The conclusions obtained in
analytical calculations are confirmed by numerical simulations on tight-binding
lattice.Comment: 9 pages, 5 figure
Josephson effect in two-band superconductors
We study theoretically the Josephson effect between two time-reversal
two-band superconductors, where we assume the equal-time spin-singlet -wave
pair potential in each conduction band. %as well as the band asymmetry and the
band hybridization in the normal state. The superconducting phase at the first
band and that at the second band characterize a
two-band superconducting state. We consider a Josephson junction where an
insulating barrier separates two such two-band superconductors. By applying the
tunnel Hamiltonian description, the Josephson current is calculated in terms of
the anomalous Green's function on either side of the junction. We find that the
Josephson current consists of three components which depend on three types of
phase differences across the junction: the phase difference at the first band
, the phase difference at the second band ,
and the difference at the center-of-mass phase .
A Cooper pairs generated by the band hybridization carries the last current
component. In some cases, the current-phase relationship deviates from the
sinusoidal function as a result of time-reversal symmetry breaking down.Comment: 6 page, 2 figure
Proximity effect in a ferromagnetic semiconductor with spin-orbit interactions
We study theoretically the proximity effect in a ferromagnetic semiconductor
with Rashba spin-orbit interaction. The exchange potential generates
opposite-spin-triplet Cooper pairs which are transformed into
equal-spin-triplet pairs by the spin-orbit interaction. In the limit of strong
spin-orbit interaction, symmetry of the dominant Cooper pair depends on the
degree of disorder in a ferromagnet. In the clean limit, spin-singlet -wave
Cooper pairs are the most dominant because the spin-momentum locking stabilizes
a Cooper pair consisting of a time-reversal partner. In the dirty limit, on the
other hand, equal-spin-triplet -wave pairs are dominant because random
impurity potentials release the locking. We also discuss the effects of the
spin-orbit interaction on the Josephson current.Comment: 9 pages, 12 figure
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