arXiv subjects

Hendrik Bentmann

Publications and source records attributed to Hendrik Bentmann.

24 records · Page 2Linked to original sources

arXiv2017

Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

A comprehensive understanding of spin-polarized photoemission is crucial for accessing the electronic structure of spin-orbit coupled materials. Yet, the impact of the final state in the photoemission process on the photoelectron spin has been difficult to assess in these systems. We present experiments for the spin-orbit split states in a Bi-Ag surface alloy showing that the alteration of the final state with energy may cause a complete reversal of the photoelectron spin polarization. We explain the effect on the basis of ab initio one-step photoemission theory and describe how it originates from linear dichroism in the angular distribution of photoelectrons. Our analysis shows that the modulated photoelectron spin polarization reflects the intrinsic spin density of the surface state being sampled differently depending on the final state, and it indicates linear dichroism as a natural probe of spin-orbit coupling at surfaces.

cond-mat.str-el↗

arXiv2016

Impurity states in the magnetic topological insulator V:(Bi,Sb)$_2$Te$_3$

The ferromagnetic topological insulator V:(Bi,Sb)$_2$Te$_3$ has been recently reported as a quantum anomalous Hall (QAH) system. Yet the microscopic origins of the QAH effect and the ferromagnetism remain unclear. One key aspect is the contribution of the V atoms to the electronic structure. Here the valence band of V:(Bi,Sb)$_2$Te$_3$ thin films was probed in an element-specific way by resonant photoemission spectroscopy. The signature of the V $3d$ impurity band was extracted, and exhibits a high density of states near Fermi level. First-principles calculations support the experimental results and indicate the coexistence of ferromagnetic superexchange and double exchange interactions. The observed impurity band is thus expected to contribute to the ferromagnetism via the interplay of different mechanisms.

cond-mat.str-el↗

arXiv2015

Termination-dependent surface properties in the giant-Rashba semiconductors BiTeX (X = Cl, Br, I)

The non-centrosymmetric semiconductors BiTeX (X = Cl, Br, I) show large Rashba-type spin-orbit splittings in their electronic structure making them candidate materials for spin-based electronics. However, BiTeI(0001) single crystal surfaces usually consist of stacking-fault-induced domains of Te and I terminations implying a spatially inhomogeneous electronic structure. Here we combine scanning tunneling microscopy (STM), photoelectron spectroscopy (ARPES, XPS) and density functional theory (DFT) calculations to systematically investigate the structural and electronic properties of BiTeX(0001) surfaces. For X = Cl, Br we observe macroscopic single-terminated surfaces. We discuss chemical characteristics among the three materials in terms of bonding character, surface electronic structure, and surface morphology.

cond-mat.mtrl-sci↗

arXiv2012

Single Dirac-cone on the Cs-covered topological insulator surface Sb2Te3(0001)

Using angle-resolved photoelectron spectroscopy we investigate the surface electronic structure of the three-dimensional topological insulator (TI) Sb2Te3(0001). Our data show the presence of a topological surface state in the bulk energy gap with the Dirac-point located above the Fermi level. The adsorption of Cs-atoms on Sb2Te3(0001) gives rise to a downward energy shift of the electronic valence band states which saturates at a value of ~200 meV. For the saturation coverage the Dirac-point of the linearly dispersive surface state resides in close proximity to the Fermi level. The electronic structure of the Cs/Sb2Te3 interface therefore considerably deviates from previously studied metal-TI interfaces based on the isostructural compound Bi2Se3 which points to the importance of atomic composition in these hetero systems.

cond-mat.mes-hall↗

arXiv2012

Direct Observation of Interband Spin-Orbit Coupling in a Two-Dimensional Electron System

We report the direct observation of interband spin-orbit (SO) coupling in a two-dimensional (2D) surface electron system, in addition to the anticipated Rashba spin splitting. Using angle-resolved photoemission experiments and first-principles calculations on Bi/Ag/Au heterostructures we show that the effect strongly modifies the dispersion as well as the orbital and spin character of the 2D electronic states, thus giving rise to considerable deviations from the Rashba model. The strength of the interband SO coupling is tuned by the thickness of the thin film structures.

cond-mat.mes-hall↗

arXiv2012

Interplay of electronic structure and atomic ordering on surfaces: Momentum-resolved measurements of Cs atoms adsorbed on a Ag(111) substrate

Surface-state mediated interactions between adsorbates on surfaces can be exploited for the fabrication of self-organized nanostructures such as two-dimensional superlattices of adatoms. Using angle-resolved photoemission we provide experimental evidence that these interactions can be drastically modified by adsorbate-induced alterations in the surface potential barrier. This, in turn, will cause significant changes in the ordering of the adsorbates. For the studied case example of Cs adatoms on Ag(111) our momentum-resolved measurements reveal the surface state Fermi wave vector to be increased by as much as $\sim$100% for coverages around 0.03 ML. Our results unravel the origin for the hitherto puzzling and unexpectedly small lattice constant in the adatom superlattice observed for this system.

cond-mat.mtrl-sci↗