On Wednesday, Sept. 17, Drs. Kuznetsova and Grebennikov discussed their investigations into topological insulators using angle-resolved photoelectron spectroscpoy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS).
Bismuth tellurohalides including BiTeI belong to a family of layered polar semiconductors lacking inversion symmetry. Much attention has recently been paid to these compounds due to the strong spin-orbit interactions of electrons caused by Bi atoms. The strong correlation between the direction of motion and spin of charge carriers (called the Rashba splitting) in materials without spatial inversion can be used in spintronic devices. The Rashba effect leads to a shift of opposite spin-polarized bands in opposite directions on the momentum scale. In the semiconductor BiTeI, the Rashba effect can be used to control the spin of charge carriers using electric fields providing a pathway for the technological development of spintronic devices.
The near surface layer of BiTeI has been converted to the three-dimensional topological insulator state by doping the surface with Cs. We studied this system by angle-resolved photoelectron spectroscopy (ARPES) and scanning tunneling spectroscopy. We analyzed the electronic structure of the (0001) surface of BiTeI and its modification upon adsorption of Cs using ARPES. A strong shift of the electronic states at the (0001) BiTeI surface by several hundred meV to higher binding energies due to band bending effects as well as the Rashba splitting are observed. Both scanning tunneling microscopy (STM) and spectroscopy (STS) show unusual atomic structures of the surfaces terminated by both tellurium and iodine atoms. Our experiments have shown that the relaxation of the surface atoms in these compounds is significant and can be used to control surface states in topological insulators.
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