Anke B. Schmidt

University of Münster

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Anke B. Schmidt has a total of 93 co-authors. Here are the top co-authors by number of shared publications:

M. Donath
12 shared publications
Markus Donath
Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
11 shared publications
Markus Donath
Universität Münster
8 shared publications
M. Pickel
6 shared publications
M. Weinelt
6 shared publications
Peter Krüger
Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
6 shared publications

Latest Publications

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Cited by 1
- 26 February 2021
- Published by American Vacuum Society in Journal of Vacuum Science & Technology A
Monolayer attenuation length of low-energy electrons in Gd and Tb
by Karen Göhler, Anke B. Schmidt, Markus Donath
The electron attenuation length is a material property, which defines the probing depth of all electron spectroscopies. For kinetic energies below 50 eV, very few data exist in the literature, although this energy range is vital for electron spectroscopy using low-energy electrons, e.g., for studying the valence electronic band structure. Extremely short attenuation lengths are expected for the transition metals gadolinium and terbium. To determine the electron attenuation length in these materials, we conducted inverse-photoemission overlayer experiments with ultrathin Gd and Tb films on W(110). For 10-eV electrons, we find an attenuation length of about one monolayer in Gd and even less in Tb, i.e., two thirds (or more) of the electrons are stopped by only one monolayer. These results imply extremely short information depths for electron spectroscopies with low energies on the lanthanides Gd and Tb.
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- 26 February 2021
- Published by American Vacuum Society in Journal of Vacuum Science & Technology A
Monolayer attenuation length of low-energy electrons in Gd and Tb
by Karen Göhler, Anke B. Schmidt, Markus Donath
The electron attenuation length is a material property, which defines the probing depth of all electron spectroscopies. For kinetic energies below 50 eV, very few data exist in the literature, although this energy range is vital for electron spectroscopy using low-energy electrons, e.g., for studying the valence electronic band structure. Extremely short attenuation lengths are expected for the transition metals gadolinium and terbium. To determine the electron attenuation length in these materials, we conducted inverse-photoemission overlayer experiments with ultrathin Gd and Tb films on W(110). For 10-eV electrons, we find an attenuation length of about one monolayer in Gd and even less in Tb, i.e., two thirds (or more) of the electrons are stopped by only one monolayer. These results imply extremely short information depths for electron spectroscopies with low energies on the lanthanides Gd and Tb.
Cited by 1
Open Access
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Cited by 30
- 8 January 2021
- Published by American Physical Society (APS) in Physical Review Research
Visualizing the multifractal wave functions of a disordered two-dimensional electron gas
by Berthold Jäck, Fabian Zinser, Elio J. König, Sune N. P. Wissing, Anke B. Schmidt, Markus Donath, Klaus Kern, Christian R. Ast
The wave functions of a disordered two-dimensional electron gas at the quantum-critical Anderson transition are predicted to exhibit multifractal scaling in their real space amplitude. We experimentally investigate the appearance of these characteristics in the spatially resolved local density of states of the two-dimensional mixed surface alloy ${Bi}_{x} {Pb}_{(1 - x)} / Ag (111)$ , by combining high-resolution scanning tunneling microscopy with spin- and angle-resolved inverse-photoemission experiments. Our detailed knowledge of the surface alloy's electronic band structure, the exact lattice structure, and the atomically resolved local density of states enables us to construct a realistic Anderson tight binding model, and to directly compare the measured local density of states characteristics with those from our model calculations. The statistical analyses of these two-dimensional local density of states maps reveal their log-normal distributions and multifractal scaling characteristics of the underlying wave functions with a finite anomalous scaling exponent. Finally, our experimental results confirm theoretical predictions of an exact scaling symmetry for Anderson quantum phase transitions in the Wigner-Dyson classes.
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- 8 January 2021
- Published by American Physical Society (APS) in Physical Review Research
Open Access
Visualizing the multifractal wave functions of a disordered two-dimensional electron gas
by Berthold Jäck, Fabian Zinser, Elio J. König, Sune N. P. Wissing, Anke B. Schmidt, Markus Donath, Klaus Kern, Christian R. Ast
The wave functions of a disordered two-dimensional electron gas at the quantum-critical Anderson transition are predicted to exhibit multifractal scaling in their real space amplitude. We experimentally investigate the appearance of these characteristics in the spatially resolved local density of states of the two-dimensional mixed surface alloy ${Bi}_{x} {Pb}_{(1 - x)} / Ag (111)$ , by combining high-resolution scanning tunneling microscopy with spin- and angle-resolved inverse-photoemission experiments. Our detailed knowledge of the surface alloy's electronic band structure, the exact lattice structure, and the atomically resolved local density of states enables us to construct a realistic Anderson tight binding model, and to directly compare the measured local density of states characteristics with those from our model calculations. The statistical analyses of these two-dimensional local density of states maps reveal their log-normal distributions and multifractal scaling characteristics of the underlying wave functions with a finite anomalous scaling exponent. Finally, our experimental results confirm theoretical predictions of an exact scaling symmetry for Anderson quantum phase transitions in the Wigner-Dyson classes.
Cited by 30
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Cited by 18
- 26 April 2018
- Published by IOP Publishing in Measurement Science and Technology
The acetone bandpass detector for inverse photoemission: operation in proportional and Geiger–Müller modes
by Christian Thiede, Iris Niehues, Anke B Schmidt, Markus Donath
Inverse photoemission is the most versatile experimental tool to study the unoccupied electronic structure at surfaces of solids. Typically, the experiments are performed in the isochromat mode with bandpass photon detectors. For gas-filled counters, the bandpass behavior is realized by the combination of the photoionization threshold of the counting gas as the high-pass filter and the ultraviolet transmission cutoff of an alkaline earth fluoride entrance window as the low-pass filter. The transmission characteristics of the entrance window determine the optical bandpass. The performance of the counter depends on the composition of the detection gas and the fill-gas pressure, the readout electronics and the counter geometry. For the well-known combination of acetone and CaF ₂ , the detector can be operated in proportional and Geiger–Müller modes. In this work, we review aspects concerning the working principles, the counter construction and the read-out electronics. We identify optimum working parameters and provide a step-by-step recipe how to build, install and operate the device.
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- 26 April 2018
- Published by IOP Publishing in Measurement Science and Technology
The acetone bandpass detector for inverse photoemission: operation in proportional and Geiger–Müller modes
by Christian Thiede, Iris Niehues, Anke B Schmidt, Markus Donath
Inverse photoemission is the most versatile experimental tool to study the unoccupied electronic structure at surfaces of solids. Typically, the experiments are performed in the isochromat mode with bandpass photon detectors. For gas-filled counters, the bandpass behavior is realized by the combination of the photoionization threshold of the counting gas as the high-pass filter and the ultraviolet transmission cutoff of an alkaline earth fluoride entrance window as the low-pass filter. The transmission characteristics of the entrance window determine the optical bandpass. The performance of the counter depends on the composition of the detection gas and the fill-gas pressure, the readout electronics and the counter geometry. For the well-known combination of acetone and CaF ₂ , the detector can be operated in proportional and Geiger–Müller modes. In this work, we review aspects concerning the working principles, the counter construction and the read-out electronics. We identify optimum working parameters and provide a step-by-step recipe how to build, install and operate the device.
Cited by 18
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Cited by 12
- 16 November 2017
- Published by American Physical Society (APS) in Physical Review Materials
Valley spin polarization of Tl/Si(111)
by Sebastian D. Stolwijk, Anke B. Schmidt, Kazuyuki Sakamoto, Peter Krüger, Markus Donath
The metal/semiconductor hybrid system Tl/Si(111)- $(1 \times 1)$ exhibits a unique Tl-derived surface state with remarkable properties. It lies within the silicon band gap and forms spin-momentum-locked valleys close to the Fermi energy at the $\bar{K}$ and ${\bar{K}}^{'}$ points. These valleys are completely spin polarized with opposite spin orientation at $\bar{K}$ and ${\bar{K}}^{'}$ and show a giant spin splitting of more than 0.5 eV. We present a detailed preparation study of the surface system and demonstrate that the electronic valleys are extremely robust, surviving exposure to 100 L hydrogen and 500 L oxygen. We investigate the influence of additional Tl atoms on the spin-polarized valleys. By combining photoemission and inverse photoemission, we prove the existence of fully spin-polarized valleys crossing the Fermi level. Moreover, these metallic valleys carry opposite Berry curvature at $\bar{K}$ and ${\bar{K}}^{'}$ , very similar to ${WSe}_{2}$ , promising a large spin Hall effect. Thus, Tl/Si(111)- $(1 \times 1)$ possesses all necessary key properties for spintronic applications.
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- 16 November 2017
- Published by American Physical Society (APS) in Physical Review Materials
Valley spin polarization of Tl/Si(111)
by Sebastian D. Stolwijk, Anke B. Schmidt, Kazuyuki Sakamoto, Peter Krüger, Markus Donath
The metal/semiconductor hybrid system Tl/Si(111)- $(1 \times 1)$ exhibits a unique Tl-derived surface state with remarkable properties. It lies within the silicon band gap and forms spin-momentum-locked valleys close to the Fermi energy at the $\bar{K}$ and ${\bar{K}}^{'}$ points. These valleys are completely spin polarized with opposite spin orientation at $\bar{K}$ and ${\bar{K}}^{'}$ and show a giant spin splitting of more than 0.5 eV. We present a detailed preparation study of the surface system and demonstrate that the electronic valleys are extremely robust, surviving exposure to 100 L hydrogen and 500 L oxygen. We investigate the influence of additional Tl atoms on the spin-polarized valleys. By combining photoemission and inverse photoemission, we prove the existence of fully spin-polarized valleys crossing the Fermi level. Moreover, these metallic valleys carry opposite Berry curvature at $\bar{K}$ and ${\bar{K}}^{'}$ , very similar to ${WSe}_{2}$ , promising a large spin Hall effect. Thus, Tl/Si(111)- $(1 \times 1)$ possesses all necessary key properties for spintronic applications.
Cited by 12
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Cited by 28
- 1 March 2017
- Published by American Physical Society (APS) in Physical Review B
Unraveling the spin structure of unoccupied states in ${Bi}_{2} {Se}_{3}$
by Christian Datzer, Anna Zumbülte, Jürgen Braun, Tobias Förster, Anke B. Schmidt, Jianli Mi, Bo Iversen, Philip Hofmann, Jan Minár, Hubert Ebert, et al.
The optical control of spin currents in topological surface states opens new perspectives in (opto-) spintronics. To understand these processes, a profound knowledge about the dispersion and the spin polarization of both the occupied and the unoccupied electronic states is required. We present a joint experimental and theoretical study on the unoccupied electronic states of the topological insulator ${Bi}_{2} {Se}_{3}$ . We discuss spin- and angle-resolved inverse-photoemission results in comparison with calculations for both the intrinsic band structure and, within the one-step model of (inverse) photoemission, the expected spectral intensities. This allows us to unravel the intrinsic spin texture of the unoccupied bands at the surface of ${Bi}_{2} {Se}_{3}$ .
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- 1 March 2017
- Published by American Physical Society (APS) in Physical Review B
Unraveling the spin structure of unoccupied states in ${Bi}_{2} {Se}_{3}$
by Christian Datzer, Anna Zumbülte, Jürgen Braun, Tobias Förster, Anke B. Schmidt, Jianli Mi, Bo Iversen, Philip Hofmann, Jan Minár, Hubert Ebert, et al.
The optical control of spin currents in topological surface states opens new perspectives in (opto-) spintronics. To understand these processes, a profound knowledge about the dispersion and the spin polarization of both the occupied and the unoccupied electronic states is required. We present a joint experimental and theoretical study on the unoccupied electronic states of the topological insulator ${Bi}_{2} {Se}_{3}$ . We discuss spin- and angle-resolved inverse-photoemission results in comparison with calculations for both the intrinsic band structure and, within the one-step model of (inverse) photoemission, the expected spectral intensities. This allows us to unravel the intrinsic spin texture of the unoccupied bands at the surface of ${Bi}_{2} {Se}_{3}$ .
Cited by 28
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Cited by 23
- 19 October 2016
- Published by American Physical Society (APS) in Physical Review B
Existence of topological nontrivial surface states in strained transition metals: W, Ta, Mo, and Nb
by Danny Thonig, Tomáš Rauch, Hossein Mirhosseini, Jürgen Henk, Ingrid Mertig, Henry Wortelen, Bernd Engelkamp, Anke B. Schmidt, Markus Donath
We show that a series of transition metals with strained body-centered cubic lattice—W, Ta, Nb, and Mo—hosts surface states that are topologically protected by mirror symmetry and, thus, exhibits nonzero topological invariants. These findings extend the class of topologically nontrivial systems by topological crystalline transition metals. The investigation is based on calculations of the electronic structures and of topological invariants. The signatures of a Dirac-type surface state in W(110), e.g., the linear dispersion and the spin texture, are verified. To further support our prediction, we investigate Ta(110) both theoretically and experimentally by spin-resolved inverse photoemission: unoccupied topologically nontrivial surface states are observed.
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- 19 October 2016
- Published by American Physical Society (APS) in Physical Review B
Existence of topological nontrivial surface states in strained transition metals: W, Ta, Mo, and Nb
by Danny Thonig, Tomáš Rauch, Hossein Mirhosseini, Jürgen Henk, Ingrid Mertig, Henry Wortelen, Bernd Engelkamp, Anke B. Schmidt, Markus Donath
We show that a series of transition metals with strained body-centered cubic lattice—W, Ta, Nb, and Mo—hosts surface states that are topologically protected by mirror symmetry and, thus, exhibits nonzero topological invariants. These findings extend the class of topologically nontrivial systems by topological crystalline transition metals. The investigation is based on calculations of the electronic structures and of topological invariants. The signatures of a Dirac-type surface state in W(110), e.g., the linear dispersion and the spin texture, are verified. To further support our prediction, we investigate Ta(110) both theoretically and experimentally by spin-resolved inverse photoemission: unoccupied topologically nontrivial surface states are observed.
Cited by 23
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Cited by 13
- 8 February 2016
- Published by American Physical Society (APS) in Physical Review B
Effects of orbital composition in a pair of spin-orbit-split surface bands at Tl/Ge(111)
by Philipp Eickholt, Peter Krüger, Sebastian D. Stolwijk, Anke B. Schmidt, Markus Donath
The spin texture of the unoccupied surface electronic structure of the metal-semiconductor hybrid system $Tl / Ge (111) - (1 \times 1)$ is investigated by spin- and angle-resolved inverse photoemission as well as quasiparticle band-structure calculations. Spin-polarized surface bands with rotating spin and giant energy splitting are found along $\bar{Γ} \bar{K} ({\bar{K}}^{'})$ , forming valleys with alternating out-of-plane spin polarization at $\bar{K}$ and ${\bar{K}}^{'}$ . This behavior is known from the equivalent hybrid system on Si(111). Along $\bar{Γ} \bar{M}$ , a pair of surface bands appears within a projected bulk band gap, whose equivalent on Tl/Si(111) is a surface resonance because, there, it overlaps with bulk states. Surprisingly, the spin splitting of these bands on Tl/Ge(111) is much smaller than on Tl/Si(111) despite the stronger surface localization and the heavier substrate. Our detailed analysis of the band structure and a tight-binding model including all relevant interactions show that a remarkable interplay between spin-orbit coupling and hybridization is responsible for this unexpected result. The comparison between the two similar hybrid systems demonstrates that the strength of the spin-orbit coupling alone, based on the atomic number of the respective elements, is not sufficient to estimate spin splittings of spin-orbit-influenced surface states.
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- 8 February 2016
- Published by American Physical Society (APS) in Physical Review B
Effects of orbital composition in a pair of spin-orbit-split surface bands at Tl/Ge(111)
by Philipp Eickholt, Peter Krüger, Sebastian D. Stolwijk, Anke B. Schmidt, Markus Donath
The spin texture of the unoccupied surface electronic structure of the metal-semiconductor hybrid system $Tl / Ge (111) - (1 \times 1)$ is investigated by spin- and angle-resolved inverse photoemission as well as quasiparticle band-structure calculations. Spin-polarized surface bands with rotating spin and giant energy splitting are found along $\bar{Γ} \bar{K} ({\bar{K}}^{'})$ , forming valleys with alternating out-of-plane spin polarization at $\bar{K}$ and ${\bar{K}}^{'}$ . This behavior is known from the equivalent hybrid system on Si(111). Along $\bar{Γ} \bar{M}$ , a pair of surface bands appears within a projected bulk band gap, whose equivalent on Tl/Si(111) is a surface resonance because, there, it overlaps with bulk states. Surprisingly, the spin splitting of these bands on Tl/Ge(111) is much smaller than on Tl/Si(111) despite the stronger surface localization and the heavier substrate. Our detailed analysis of the band structure and a tight-binding model including all relevant interactions show that a remarkable interplay between spin-orbit coupling and hybridization is responsible for this unexpected result. The comparison between the two similar hybrid systems demonstrates that the strength of the spin-orbit coupling alone, based on the atomic number of the respective elements, is not sufficient to estimate spin splittings of spin-orbit-influenced surface states.
Cited by 13
Open Access
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Cited by 12
- 3 August 2015
- Published by American Physical Society (APS) in Physical Review B
Spin-polarized surface electronic structure of Ta(110): Similarities and differences to W(110)
by B. Engelkamp, H. Wortelen, H. Mirhosseini, A. B. Schmidt, D. Thonig, J. Henk, M. Donath
Tantalum and tungsten, direct neighbors in the periodic table, exhibit a very similar electronic structure. Compared with tungsten, however, the bands of tantalum are less occupied due to the lack of one electron. As a consequence, an exceptional Dirac-cone-like surface state, observed below the Fermi level for W(110), may appear above the Fermi level for Ta(110). To prove this conjecture, we investigate the unoccupied surface electronic structure of Ta(110) by spin- and angle-resolved inverse photoemission and electronic-structure calculations. Surprisingly, our results do not show the expected Dirac-cone-like surface state. Instead, spin-polarized unoccupied surface bands are identified, which have no equivalent in W(110). These findings are explained by the difference in the energetic positions of the surface states relative to the bulk states for Ta(110) and W(110) caused by the different lattice constants.
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- 3 August 2015
- Published by American Physical Society (APS) in Physical Review B
Open Access
Spin-polarized surface electronic structure of Ta(110): Similarities and differences to W(110)
by B. Engelkamp, H. Wortelen, H. Mirhosseini, A. B. Schmidt, D. Thonig, J. Henk, M. Donath
Tantalum and tungsten, direct neighbors in the periodic table, exhibit a very similar electronic structure. Compared with tungsten, however, the bands of tantalum are less occupied due to the lack of one electron. As a consequence, an exceptional Dirac-cone-like surface state, observed below the Fermi level for W(110), may appear above the Fermi level for Ta(110). To prove this conjecture, we investigate the unoccupied surface electronic structure of Ta(110) by spin- and angle-resolved inverse photoemission and electronic-structure calculations. Surprisingly, our results do not show the expected Dirac-cone-like surface state. Instead, spin-polarized unoccupied surface bands are identified, which have no equivalent in W(110). These findings are explained by the difference in the energetic positions of the surface states relative to the bulk states for Ta(110) and W(110) caused by the different lattice constants.
Cited by 12
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Cited by 9
- 1 August 2015
- Published by AIP Publishing in Review of Scientific Instruments
Optimizing the performance of bandpass photon detectors for inverse photoemission: Transmission of alkaline earth fluoride window crystals
by Christian Thiede, Anke B. Schmidt, Markus Donath
Bandpass photon detectors are widely used in inverse photoemission in the isochromat mode at energies in the vacuum-ultraviolet spectral range. The energy bandpass of gas-filled counters is usually formed by the ionization threshold of the counting gas as high-pass filter and the transmission cutoff of an alkaline earth fluoride window as low-pass filter. The transmission characteristics of the window have, therefore, a crucial impact on the detector performance. We present transmission measurements in the vacuum-ultraviolet spectral range for alkaline earth fluoride window crystals in the vicinity of the transmission cutoff as a function of crystal purity, surface finish, surface contamination, temperature, and thickness. Our findings reveal that the transmission characteristics of the window crystal and, thus, the detector performance depend critically on these window parameters.
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- 1 August 2015
- Published by AIP Publishing in Review of Scientific Instruments
Optimizing the performance of bandpass photon detectors for inverse photoemission: Transmission of alkaline earth fluoride window crystals
by Christian Thiede, Anke B. Schmidt, Markus Donath
Bandpass photon detectors are widely used in inverse photoemission in the isochromat mode at energies in the vacuum-ultraviolet spectral range. The energy bandpass of gas-filled counters is usually formed by the ionization threshold of the counting gas as high-pass filter and the transmission cutoff of an alkaline earth fluoride window as low-pass filter. The transmission characteristics of the window have, therefore, a crucial impact on the detector performance. We present transmission measurements in the vacuum-ultraviolet spectral range for alkaline earth fluoride window crystals in the vicinity of the transmission cutoff as a function of crystal purity, surface finish, surface contamination, temperature, and thickness. Our findings reveal that the transmission characteristics of the window crystal and, thus, the detector performance depend critically on these window parameters.
Cited by 9
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Cited by 24
- 16 June 2015
- Published by American Physical Society (APS) in Physical Review B
Spin texture with a twist in momentum space for Tl/Si(111)
by Sebastian D. Stolwijk, Kazuyuki Sakamoto, Anke B. Schmidt, Peter Krüger, Markus Donath
The electronic structure and spin texture around the $\bar{M}$ point of $Tl / Si (111) − (1 \times 1)$ is investigated with spin- and angle-resolved inverse photoemission and density-functional theory. The $Tl / Si (111) − (1 \times 1)$ surface exhibits a surface-derived unoccupied state, which extends over the complete surface Brillouin zone. It is known for its giant spin-orbit-induced splitting and unique symmetry- and spin-orbit-induced spin landscape: a rotating spin pattern in momentum space along $\bar{Γ} \bar{K}$ and pure in-plane spin polarization along $\bar{Γ} \bar{M}$ . Our results demonstrate how the $\bar{M}$ point is encircled by this state. Its spin texture shows a peculiar twist, which reflects the $C_{1 h}$ symmetry of the $\bar{M}$ point.
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- 16 June 2015
- Published by American Physical Society (APS) in Physical Review B
Spin texture with a twist in momentum space for Tl/Si(111)
by Sebastian D. Stolwijk, Kazuyuki Sakamoto, Anke B. Schmidt, Peter Krüger, Markus Donath
The electronic structure and spin texture around the $\bar{M}$ point of $Tl / Si (111) − (1 \times 1)$ is investigated with spin- and angle-resolved inverse photoemission and density-functional theory. The $Tl / Si (111) − (1 \times 1)$ surface exhibits a surface-derived unoccupied state, which extends over the complete surface Brillouin zone. It is known for its giant spin-orbit-induced splitting and unique symmetry- and spin-orbit-induced spin landscape: a rotating spin pattern in momentum space along $\bar{Γ} \bar{K}$ and pure in-plane spin polarization along $\bar{Γ} \bar{M}$ . Our results demonstrate how the $\bar{M}$ point is encircled by this state. Its spin texture shows a peculiar twist, which reflects the $C_{1 h}$ symmetry of the $\bar{M}$ point.
Cited by 24

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