Electronic band structure, magnetic and structural properties of magnetic atoms on Bi2Se3Cux
Physical Chemistry of Solids and Surfaces, Material Characterisation
Final Report Abstract
In this project, the experimental realization of breaking the time-reversal (TR) symmetry at the surface of three-dimensional topological insulators (TI) has been attempted. Several theoretical studies predict RKKY magnetic coupling between magnetic adatoms, where it is efficiently mediated by the topological surface state (TSS). Prior to this project, experiments have failed in the realization of the predicted effect. We suspected the presence of a non-topological (trivial) 2DEG at the surface to be responsible for the discrepancy between theoretical and experimental results. The original plan of this project was to use degenerate version of Bi2Se3 (Cu-doped) where no 2DEG is created as an alternative to the non-degenerate Bi2Se3. Ni, Fe, and Co atoms have been adsorbed separately with different coverage. To study the magnetic properties we used the X-ray Magnetic Circular Dichroism (XMCD) technique. A detailed XCMD analysis reveals rather a paramagnetic behavior of all studied systems. We attributed the absence of magnetic coupling to the interaction of the TSS with conduction electrons of the degenerate Bi 2 Se 3 . As the main aim of the project is to create magnetic ordering at the TI surface, a change of the initial work plan had to be done. Thus, another TI, namely Bi2Te2Se, has been selected for further analysis. Bi2Te2Se is a non-degenerate semiconductor where the 2DEG creation is avoided. After successful ex-situ growth of Bi2Te2Se crystals, XMCD measurements have been performed following similar experimental procedure as for the Cu-doped Bi2Se3. Here also, the magnetic properties did not match the predicted magnetic phase. In analogy with electronic transport works, we explained it by the interaction with valence band electrons that contribute to surface currents, as well. Hence, an ultimate test should be the use a TI, where all bulk and 2DEG interactions with the TSS are effectively minimized. The non-degenerate Bi2-xSbxTe2SeTI crystal has been chosen for the test. The TSS of Bi2-xSbxTe2Se is well separated from the bulk states. The obtained results from the XMCD investigation show here again no magnetic ordering as expected by theory. In conclusion, the work performed in this project makes a step forward towards the realization of TR symmetry breaking at the surface of TI. It provides a detailed overview of surface magnetic properties of different magnetic adatoms on three TIs having different TSS electronic properties. Furthermore, it shows that the experimental realization of the predicted TR symmetry breaking via surface magnetic ordering stays ineffective even when TSS interaction with trivial states is avoided and suggests the usage of alternative recipes.
Publications
- Dimensional crossover in the quantum transport behavior of the natural topological insulator Aleksite. Nature, Sci. Rep. 5, 11691 (2015)
P. Gehring, K. Vaklinova, A. Hoyer, H.M. Benia, V. Skakalova, Gi. Argentero, F. Eder, J.C. Meyer, M. Burghard, K. Kern
(See online at https://doi.org/10.1038/srep11691) - Surface band structure of the Bi 1-xSbx system. PRB 91, 161406 (2015)
H.M. Benia, C. Straßer, K. Kern, C.R. Ast
(See online at https://doi.org/10.1103/PhysRevB.91.161406) - Intercalation of graphene on SiC(0001) via ion implantation. Phys. Rev. B 94, 085431 – Published 31 August 2016
A. Stöhr, S. Forti, S. Link, A. A. Zakharov, K. Kern, U. Starke, H.M. Benia
(See online at https://doi.org/10.1103/PhysRevB.94.085431) - Observation of Dirac surface states in the noncentrosymmetric superconductor BiPd
H. M. Benia, E. Rampi, C. Trainer, C. M. Yim, A. Maldonado, D. C. Peets, A. Stoehr, U. Starke, K. Kern, A. Yaresko, G. Levy, A. Damascelli, C. R. Ast, A. P. Schnyder, P. Wahl
- Wedge Dyakonov Waves and Dyakonov Plasmons in Topological Insulator Bi2Se3 Probed by Electron Beams. ACS Nano 10 (7), 6988 (2016)
N. Talebi, C. Ozsoy-Keskinbora, H. M. Benia, K. Kern, C. T. Koch, and P. A. van Aken
(See online at https://doi.org/10.1021/acsnano.6b02968)
