From semiconductor nanocrystals to artificial graphene and topological insulator
Guy Allan a, Christophe Delerue a, Efterpi Kalesaki a, Cristiane Morais Smith b, Wouter Beugeling b, Daniel Vanmaekelbergh b
a IEMN - Dept. ISEN, 41 boulevard Vauban, Lille Cedex, 59046, France
Invited Speaker, Christophe Delerue, presentation 049
Publication date: 27th June 2014

Recent advancements in colloidal chemistry indicate that two-dimensional single-crystalline sheets of semiconductors forming a honeycomb lattice can be synthesized from semiconductor nanocrystals [1]. We perform atomistic tight-binding calculations of the band structure of CdSe sheets with such a nano-geometry [2]. We predict in the conduction band Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has s-orbital character and is equivalent to the pi bands of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their p-orbital character. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. In particular, we present recent calculations on Ge lattices [3]. We demonstrate that the combination of the honeycomb geometry and the strong spin-orbit coupling leads to the formation of bands with nontrivial topology. Model systems are studied in order to understand the origin of these unconventional properties.

[1] W. H. Evers, B. Goris, S. Bals, M. Casavola, J. de Graaf, R. van Roij, M. Dijkstra, and D. Vanmaekelbergh, Nano Lett. 13, 2317 (2013).

[2] E. Kalesaki, C. Delerue, C. Morais Smith, W. Beugeling, G. Allan, D. Vanmaekelbergh, Phys. Rev. X 4, 011010 (2014).

[3] C. Delerue, to be published.



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