VietNam 2013 

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


 Nanophysics: from fundamentals to applications

(the return)


Thursday 8
Topological Insulators

› 8:30 - 9:00 (30min)
HgTe as a topological insulator
Laurens Molenkamp  1@  
1 : Wuerzburg University, Physics Institute, EP3
Am Hubland, D - 97074 Wuerzburg -  Germany

HgTe is a zincblende-type semiconductor with an inverted band structure. While the bulk material is a semimetal, lowering the crystalline symmetry opens up a gap, turning the compound into a topological insulator.

The most straightforward way to do so is by growing a quantum well with (Hg,Cd)Te barriers. Such structures exhibit the quantum spin Hall effect, where a pair of spin polarized helical edge channels develops when the bulk of the material is insulating.

Our transport data[1-3] provide very direct evidence for the existence of this third quantum Hall effect, which now is seen as the prime manifestation of a 2-dimensional topological insulator.

To turn the material into a 3-dimensional topological insulator, we utilize growth induced strain in relatively thick (ca. 100 nm) HgTe epitaxial layers. The high electronic quality of such layers allows a direct observation of the quantum Hall effect of the 2-dimensional topological surface states[4]. Moreover, on contacting these structures with Nb electrodes, a supercurrent is induced in the surface states. 


[1] M. König, et al., Science 318, 766 (2007).

[2] A. Roth, et al., Science 325, 294 (2009).

[3] C. Brüne, et al., Nature Physics 8, 486 (2012).

[4] C. Brüne, et al., Phys. Rev. Lett. 106, 126803 (2011).

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