Contact

Fecher, Gerhard
Gerhard Fecher
Senior Chief Research Officer
Phone: +49 351 4646-2240
Fax: +49 351 4646-3002

Physics, Electronic structure

Publication highlights

1.
R. Shan, S. Ouardi, G. H. Fecher, L. Gao, A. Kellock, K. P. Roche, M. G. Samant, C. E. ViolBarbosa, E. Ikenaga, C. Felser, and S. S. P. Parkin, "Electronic and crystalline structures of zero band-gap LuPdBi thin films grown epitaxially on MgO(100)," Applied Physics Letters 102, 172401-1-172401-4 (2013).
2.
Siham Ouardi, Chandra Shekhar, Gerhard H. Fecher, Xeniya Kozina, Gregory Stryganyuk, Claudia Felser, Shigenori Ueda, and Keisuke Kobayashi, "Electronic structure of Pt based topological Heusler compounds with C1b structure and "zero band gap"," Applied Physics Letters 98 (21), 1-3 (2011).
3.
C. E. ViolBarbosa, C. Shekhar, B. Yan, S. Ouardi, E. Ikenaga, G. H. Fecher, and C. Felser, "Direct observation of band bending in the topological insulator Bi2Se3," Physical Review B 88 (19), 195128-1-195128-4 (2013).

Topological Insulators

“zero-gap” Semiconductors

Theoretical predictions in novel material, like topological insulators, are also investigated by HAXPES. The comparison between HAXPES valence band spectra and ab initio calculations shows clear evidence of zero band gap states in C1b Heuslers: LuPdBi, PtYSb and PtLaBi.  The zero band gap is resulted from the cubic symmetry and is a signature of  band inversion, which is an essential feature for a topological insulator state [1][2].

<p style="text-align: justify;"><strong>Figure 1:</strong> <em>Valence band of LuPdBi. (a) and (b) HAXPES spectra. (c) and (d)  Ab inition density of states, and the density localized at the Pd atoms is marked by the shaded area.</em></p> Zoom Image

Figure 1: Valence band of LuPdBi. (a) and (b) HAXPES spectra. (c) and (d)  Ab inition density of states, and the density localized at the Pd atoms is marked by the shaded area.

Band bending in Topological Insulator

Theoretical predictions in novel material, like topological insulators and Weyl semiconductors, are also investigated by HAXPES. In this example, HAXPES allows a direct measurement of the surface band bending in Bi2Se3. The existence of a band bending was predicted to be the origin of additional surface states, exhibiting considerable Rashba splitting, nested in the Dirac cone. The band bending was demonstrated by tracking the depth dependence of the core energy shift of the material [3].

<p style="text-align: justify;"><strong>Figure 2:</strong> <em>EDC for Se 2p3/2 core state. The energy shift indicate a indicates a downward bending from bulk to surface.</em></p> Zoom Image

Figure 2: EDC for Se 2p3/2 core state. The energy shift indicate a indicates a downward bending from bulk to surface.

 
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