TY  - JOUR
A1  - Geissler, F.
A1  - Budich, J. C.
A1  - Trauzettel, B.
T1  - Group theoretical and topological analysis of the quantum spin Hall effect in silicene
JF  - New Journal of Physics
N2  - Silicene consists of a monolayer of silicon atoms in a buckled honeycomb structure. It was recently discovered that the symmetry of such a system allows for interesting Rashba spin–orbit effects. A perpendicular electric field is able to couple to the sublattice pseudospin, making it possible to electrically tune and close the band gap. Therefore, external electric fields may generate a topological phase transition from a topological insulator to a normal insulator (or semimetal) and vice versa. The contribution of the present paper to the study of silicene is twofold. Firstly, we perform a group theoretical analysis to systematically construct the Hamiltonian in the vicinity of the K points of the Brillouin zone and find an additional, electric field induced spin–orbit term, that is allowed by symmetry. Subsequently, we identify a tight-binding model that corresponds to the group theoretically derived Hamiltonian near the K points. Secondly, we start from this tight-binding model to analyze the topological phase diagram of silicene by an explicit calculation of the Z2 topological invariant of the band structure. To this end, we calculate the Z2 topological invariant of the honeycomb lattice in a manifestly gauge invariant way which allows us to include Sz symmetry breaking terms—like Rashba spin–orbit interaction—into the topological analysis. Interestingly, we find that the interplay of a Rashba and an intrinsic spin–orbit term can generate a non-trivial quantum spin Hall phase in silicene. This is in sharp contrast to the more extensively studied honeycomb system graphene where Rashba spin–orbit interaction is known to compete with the quantum spin Hall effect in a detrimental way.
KW  - quantum spin
KW  - Hall effect
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129732
VL  - 15
IS  - 085030
ER  - 
TY  - JOUR
A1  - Varykhalov, A.
A1  - Marchenko, D.
A1  - Sánchez-Barriga, J.
A1  - Scholz, M. R.
A1  - Verberck, B.
A1  - Trauzettel, B.
A1  - Wehling, T. O.
A1  - Carbone, C.
A1  - Rader, O.
T1  - Intact Dirac Cones at Broken Sublattice Symmetry: Photoemission Study of Graphene on Ni and Co
JF  - Physical Review X
N2  - The appearance of massless Dirac fermions in graphene requires two equivalent carbon sublattices of trigonal shape. While the generation of an effective mass and a band gap at the Dirac point remains an unresolved problem for freestanding extended graphene, it is well established by breaking translational symmetry by confinement and by breaking sublattice symmetry by interaction with a substrate. One of the strongest sublattice-symmetry-breaking interactions with predicted and measured band gaps ranging from 400 meV to more than 3 eV has been attributed to the interfaces of graphene with Ni and Co, which are also promising spin-filter interfaces. Here, we apply angle-resolved photoemission to epitaxial graphene on Ni (111) and Co(0001) to show the presence of intact Dirac cones 2.8 eV below the Fermi level. Our results challenge the common belief that the breaking of sublattice symmetry by a substrate and the opening of the band gap at the Dirac energy are in a straightforward relation. A simple effective model of a biased bilayer structure composed of graphene and a sublattice-symmetry-broken layer, corroborated by density-functional-theory calculations, demonstrates the general validity of our conclusions.
KW  - NI(111)
KW  - ultrasoft pseudopotentials
KW  - monolayer graphite
KW  - electronic states
KW  - transistors
KW  - surface
Y1  - 2012
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-135732
VL  - 2
IS  - 041017
ER  -