Probing the surface structure of the three dimensional topological insulator TlBiSe2

Thursday, 10 September 2015 at 14:00 in Y36 K08

A newly discovered class of materials called topological insulators (TI) has become prominent in recent years due to the presence of a Dirac-­cone-like surface state at the Fermi level. These surface states are emerging due to a band inversion triggered by strong spin orbit coupling. Their resistance against non-­magnetic surface contamination and their high spin polarization have raised hope of integrating these materials in future spintronic devices.
So far the majority of TI have been layered quasi-­2D crystals with strong chemical bonding inside the layers and van-­der-­Waals forces perpendicular to the surface. On one hand, the presence of a van-­der-­Waals-­gap allows for the modification of the material by intercalating atoms, on the other hand unwanted intercalation may change the properties of the material. A few years after the discovery of layered TI, 3D non-­layered crystals like TlBiSe2 were discovered to possess topological surface states too. However, their lattices are lacking preferential cleaving planes, sparking interest in the termination and overall nature of the fractured surface of materials like TlBiSe2. The knowledge of the surface structure is even more important in the present material since their experimental electronic structure is not accurately reproduced by Density Functional Theory (DFT) calculations, which are based on simple surface termination scenarios [1].
In this seminar I will present our ongoing work regarding the topological insulator TlBiSe2, from its discovery by Angle and Spin resolved photoelectron spectroscopy [2], via our demonstration, that its surface structure is dominated by island like structures which are most likely composed by Tl atoms [3] towards recent high resolution x-­ray photoelectron diffraction (XPD) measurements that allowed us to unambiguously determine the surface termination of TlBiSe2. Finally I will give an outlook how our structural determination together with scanning tunneling spectroscopy (STS) can inform DFT calculations leading to a more accurate description of the surface state structure.

[1] Eremeev et al., Physical Review B 83, 205129 (2011)
[2] K. Kuroda et al., Physical Review Letters 105, 146801 (2010)
[3] Kuroda et al., Physical Review B 88, 245308 (2013)