157 research outputs found
Dirac Theory and Topological Phases of Silicon Nanotube
Silicon nanotube is constructed by rolling up a silicene, i.e., a monolayer
of silicon atoms forming a two-dimensional honeycomb lattice. It is a
semiconductor or an insulator owing to relatively large spin-orbit interactions
induced by its buckled structure. The key observation is that this buckled
structure allows us to control the band structure by applying electric field
. When is larger than a certain critical value , by
analyzing the band structure and also on the basis of the effective Dirac
theory, we demonstrate the emergence of four helical zero-energy modes
propagating along nanotube. Accordingly, a silicon nanotube contains three
regions, namely, a topological insulator, a band insulator and a metallic
region separating these two types of insulators. The wave function of each zero
mode is localized within the metallic region, which may be used as a quantum
wire to transport spin currents in future spintronics. We present an analytic
expression of the wave function for each helical zero mode. These results are
applicable also to germanium nanotube.Comment: 5 pages, 5 figure
Single Dirac-Cone State and Quantum Hall Effects in Honeycomb Structure
A honeycomb lattice system has four types of Dirac electrons corresponding to
the spin and valley degrees of freedom. We consider a state that contains only
one type of massless electrons and three types of massive ones, which we call
the single Dirac-cone state. We analyze quantum Hall (QH) effects in this
state. We make a detailed investigation of the Chern and spin-Chern numbers. We
make clear the origin of unconventional QH effects discovered in graphene. We
also show that the single Dirac-cone state may have arbitrary large spin-Chern
numbers in magnetic field. Such a state will be generated in antiferromagnetic
transition-metal oxides under electric field or silicene with antiferromagnetic
order under electric field.Comment: 5 pages, 5 figure
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