7 research outputs found
Weak topological insulator with protected gapless helical states
A workable model for describing dislocation lines introduced into a
three-dimensional topological insulator is proposed. We show how fragile
surface Dirac cones of a weak topological insulator evolve into protected
gapless helical modes confined to the vicinity of dislocation line. It is
demonstrated that surface Dirac cones of a topological insulator (either strong
or weak) acquire a finite-size energy gap, when the surface is deformed into a
cylinder penetrating the otherwise surface-less system. We show that when a
dislocation with a non-trivial Burgers vector is introduced, the finite-size
energy gap play the role of stabilizing the one-dimensional gapless states.Comment: 8 pages, 17 figure
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
Spherical topological insulator
The electronic spectrum on the spherical surface of a topological insulator
reflects an active property of the helical surface state that stems from a
constraint on its spin on a curved surface. The induced effective vector
potential (spin connection) can be interpreted as an effective vector potential
associated with a fictitious magnetic monopole induced at the center of the
sphere. The strength of the induced magnetic monopole is found to be g=2pi,
-2pi, being the smallest finite (absolute) value compatible with the Dirac
quantization condition. We have established an explicit correspondence between
the bulk Hamiltonian and the effective Dirac operator on the curved spherical
surface. An explicit construction of the surface spinor wave functions implies
a rich spin texture possibly realized on the surface of topological insulator
nanoparticles. The electronic spectrum inferred by the obtained effective
surface Dirac theory, confirmed also by the bulk tight-binding calculation,
suggests a specific photo absorption/emission spectrum of such nanoparticles.Comment: 13 pages, 2 figure