(Invited) Topological States in Multi-Orbital Honeycomb Lattices of HgTe (CdTe) Quantum Dots

Monday, October 12, 2015: 14:30
105-B (Phoenix Convention Center)
W. Beugeling (MPIPKS Dresden, Utrecht University), E. Kalesaki (University of Luxembourg, IEMN Lille), C. Delerue (IEMN Dept. ISEN CNRS Lille), Y. M. Niquet (CEA INAC Grenoble), D. Vanmaekelbergh (Utrecht University), and C. Morais Smith (Utrecht University)
Recent advancements in colloidal chemistry demonstrate that two-dimensional single-crystalline sheets of semiconductors forming a honeycomb lattice can be synthesized by oriented attachment of semiconductor nanocrystals [1,2]. Inspired by these results, we have performed atomistic tight-binding calculations of the band structure of CdSe [3,4] and HgTe [5] sheets with honeycomb nano-geometry. We have also considered honeycomb super-lattices of quantum dots that could be made using nano-lithography of HgTe layers.

In the case of CdSe sheets [3], we predicted that their conduction band exhibits Dirac cones at two distinct energies and nontrivial flat bands. The lowest Dirac conduction band has s-orbital character and is equivalent to the π 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.

We also present very recent results on HgTe [5]. We show theoretically that honeycomb lattices of HgTe can combine the effects of the honeycomb geometry and strong spin-orbit coupling. The conduction bands, experimentally accessible via doping, can be described by a tight-binding lattice model as in graphene, but including multi-orbital degrees of freedom and spin-orbit coupling. This results in very large topological gaps (up to 35 meV) and a flattened band detached from the others. Owing to this flat band and the sizable Coulomb interaction, honeycomb structures of HgTe quantum dots constitute a promising platform for the observation of a fractional Chern insulator or a fractional quantum spin Hall phase.

[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] M. P. Boneschanscher, W. H. Evers, J. J. Geuchies, T. Altantzis, B. Goris, F. T. Rabouw, S. A. P. van Rossum, H. S. J. van der Zant, L. D. A. Siebbeles, G. Van Tendeloo, I. Swart, J. Hilhorst, A. V. Petukhov, S. Bals, and D. Vanmaekelbergh, Science 344, 1377-1380 (2014).

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

[4] C. Delerue, Phys. Chem. Chem. Phys., 2014, doi: 10.1039/C4CP01878H.

[5] Beugeling, W. et al, Nat. Commun. 6:6316 doi: 10.1038/ncomms7316 (2015).