VietNam 2013 

IXth Rencontres du Vietnam
Quy-Nhon, August 4-10, 2013


 Nanophysics: from fundamentals to applications

(the return)


Thursday 8
Topological Insulators

› 10:30 - 11:00 (30min)
Observation of topological surface states of strained HgTe and their circular dichroism.
Olivier Crauste  1@  , Yoshiyuki Ohtsubo  2@  , Amina Taleb  2@  , Philippe Ballet  3@  , Pierre-André Delplace  4@  , David Carpentier  5@  , Tristan Meunier  1@  , Clément Bouvier  1@  , Laurent Lévy  1@  
1 : Institut Néel, CNRS and Univ. J. Fourier  -  Website
CNRS : UPR2940
25 Avenue des Martyrs BP166 38042, Grenoble Cedex 9 -  France
2 : Synchrotron SOLEIL  (SSOLEIL)  -  Website
L'Orme des Merisiers Saint-Aubin - BP 48 91192 GIF-sur-YVETTE CEDEX -  France
3 : Laboratoire d'Electronique et des Technologies de l'Information  (LETI)
MINATEC 17, rue des Martyrs, 38054, Grenoble Cedex 9 -  France
4 : Université de Genève  -  Website
24 rue du Général-Dufour CH - 1211 Genève 4 -  Switzerland
5 : Laboratoire de Physique de l'ENS Lyon  (Phys-ENS)  -  Website
CNRS : UMR5672, École Normale Supérieure - Lyon
46 allée d'Italie 69007 Lyon -  France

Mercury Telluride has been predicted to be a topological insulator when strained. When grown epitaxially on the surface of CdTe, HgTe is homogenously stressed up to slab thicknesses of 200 nm. We have performed angle-resolved photoemission on a serie of strained HgTe 100nm thick slabs grown on CdTe with different crystal orientation ([100] and [211]). We observe very strong surface states which Dirac point sits exactly at the top of the $\Gamma_8$ heavy hole band, leaving one half of the Dirac cone inside the strain gap and the other half inside the bulk $\gamma_8$ heavy-hole band. These observations have been confirmed by a discrete analysis of the 8-band Kane model close to the $\Gamma$ point.The observed band velocity 0.46eV/nm is slightly smaller than expected theoretically. The measured strain-gap (70 meV) between the $\Gamma_8$ light and heavy holes bands is more than twice the value expected. Surprizingly enough, the surface states have a linear dispersion in the $\Gamma$-X direction all the way to the X point.

We have also measured the circular dichroism of the surface and bulk bands. We find a very strong circular dichroism of the bulk $\Gamma_8$-heavy hole band, attributed to the surface assymetry. This proves that bulk bands are also spin-polarized.

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