Paper MI-TuM11
Energy Dispersion and Spin Structure of Unoccupied Electronic States of BiTeI: A Matter of Surface Termination?

Tuesday, October 20, 2015, 11:20 am, Room 230A

Recently, a new class of “Rashba materials” has been discovered: Non-centrosymmetric materials like MoS₂ [1] and BiTeI [2] show a lifting of the spin degeneracy in the electronic structure due to the bulk Rashba effect. So far, studies on BiTeI are limited to the occupied band regime and its Rashba-type spin dependence. For future applications, e.g. opto-spintronics, a substantiated knowledge about the complete spin-dependent electronic structure, occupied as well as unoccupied, is needed.

We present a combined experimental and theoretical study on the unoccupied electronic structure of BiTeI along the Γ-K direction. In our spin-resolved inverse photoemission measurements, we found a strong influence of the sample quality on the energy dispersion around the Γ point. Based on band structure calculations, we attribute this effect to different surface terminations, Te or I. Due to band bending, the different terminations have a direct consequence for the band dispersion. This effect is not observed at K, where the spectra do not depend on the surface quality. We will discuss this result in the context of ab initio band structure calculations. - In addition, we studied the spin structure of the bands along Γ-K. Around the Γ point, we found in-plane spin polarization in agreement with previous photoemission experiments for the occupied states [2]. Upon approaching K, the direction of the spin polarization rotates from in-plane to fully out-of-plane in accordance with the crystal symmetry.

[1] Suzuki et al., Nature Nanotechnology 9, 611 (2014)