Introduction: Why Should We Study Migration Policies at the Interface between Empirical Research and Normative Analysis?

The text introduces the concept behind the Proceedings of the 2018 ZiF Workshop “Studying Migration Policies at the Interface between Empirical Research and Normative Analysis”. It explains why there is a need to study migration policies across disciplines, includes a short note on the current literature, and provides a look back at the workshop. DOI:10.17879/1519962468

Geschichte und Theodizee bei Kant

Kant löst das Theodizee-Problem, indem er es als unlösbar erweist und zugleich der Vernunft den „Machtspruch“ vorbehält, am Glauben festzuhalten. Gleichwohl findet sich in den geschichtsphilosophischen Schriften der Versuch, Unrecht in der Geschichte durch seine zweckmäßige Ausrichtung auf einen Endzustand zu rechtfertigen. Beide Positionen können nur durch eine problematische Konstruktion der „Naturabsicht“ vereinigt werden, die aus einer Säkularisierung des Vorsehungsbegriffs resultiert

Giant Kohn anomaly and the phase transition in charge density wave ZrTe_3

A strong Kohn anomaly in ZrTe_3 is identified in the mostly transverse acoustic phonon branch along the modulation vector q_P with polarization along the a* direction. This soft mode freezes to zero frequency at the transition temperature T_P and the temperature dependence of the frequency is strongly affected by fluctuation effects. Diffuse x-ray scattering of the incommensurate superstructure shows a power law scaling of the intensity and the correlation length that is compatible with an order parameter of dimension n = 2.Comment: 4 pages, 4 figures. accepted at Phys. Rev. Let

Buried double CuO chains in YBa2_2Cu4_4O8_8 uncovered by nano-ARPES

The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate systems by means of standard angle-resolved photoemission spectroscopy (ARPES); cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and the size of a typical beam results in ARPES signals that are superposed from both terminations. Here, we employ spatially-resolved ARPES with submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in YBa$_2$Cu$_4$O$_8$. We present the first observation of sharp metallic dispersions and Fermi surfaces of the double CuO chains buried underneath the CuO$_2$-plane block on the BaO terminated surface. While the observed Fermi surfaces of the CuO chains are highly one-dimensional, the electrons in the CuO-chains do not undergo significant electron correlations and no signature of a Tomonaga-Luttinger liquid nor a marginal Fermi liquid is found. Our works represent an important experimental step toward understanding of the charge dynamics and provides a starting basis for modelling the high-$T_c$ superconductivity in YBCO cuprate systems.Comment: 10 pages, 5 figures including supplementary material (4 pages, 2 figures

dxz/yzd_{xz/yz} Orbital Subband Structures and Chiral Orbital Angular Momentum in the (001) Surface States of SrTiO3_3

We have performed angle resolved photoemission spectroscopy (ARPES) experiments on the surface states of SrTiO$_3$(001) using linearly and circularly polarized light to investigate the subband structures of out-of-plane $d_{xz/yz}$ orbitals and chiral orbital angular momentum (OAM). The data taken in the first Brillouin zone reveal new subbands for $d_{xz/yz}$ orbitals with Fermi wave vectors of 0.25 and 0.45 $\mathrm{\AA}^{-1}$ in addition to the previously reported ones. As a result, there are at least two subbands for all the Ti 3d t$_{2g}$ orbitals. Our circular dichroism ARPES data is suggestive of a chiral OAM structure in the surface states and may provide clues to the origin of the linear Rashba-like surface band splitting.Comment: 7 pages, 3 figures, Journal pape

Short-Range Correlations in Magnetite above the Verwey Temperature

Magnetite, Fe$_3$O$_4$, is the first magnetic material discovered and utilized by mankind in Ancient Greece, yet it still attracts attention due to its puzzling properties. This is largely due to the quest for a full and coherent understanding of the Verwey transition that occurs at $T_V=124$ K and is associated with a drop of electric conductivity and a complex structural phase transition. A recent detailed analysis of the structure, based on single crystal diffraction, suggests that the electron localization pattern contains linear three-Fe-site units, the so-called trimerons. Here we show that whatever the electron localization pattern is, it partially survives up to room temperature as short-range correlations in the high-temperature cubic phase, easily discernible by diffuse scattering. Additionally, {\it ab initio} electronic structure calculations reveal that characteristic features in these diffuse scattering patterns can be correlated with the Fermi surface topology.Comment: 7 pages, 6 figure

Suppression of orbital ordering by chemical pressure in FeSe1-xSx

We report a high-resolution angle-resolved photo-emission spectroscopy study of the evolution of the electronic structure of FeSe1-xSx single crystals. Isovalent S substitution onto the Se site constitutes a chemical pressure which subtly modifies the electronic structure of FeSe at high temperatures and induces a suppression of the tetragonal-symmetry-breaking structural transition temperature from 87K to 58K for x=0.15. With increasing S substitution, we find smaller splitting between bands with dyz and dxz orbital character and weaker anisotropic distortions of the low temperature Fermi surfaces. These effects evolve systematically as a function of both S substitution and temperature, providing strong evidence that an orbital ordering is the underlying order parameter of the structural transition in FeSe1-xSx. Finally, we detect the small inner hole pocket for x=0.12, which is pushed below the Fermi level in the orbitally-ordered low temperature Fermi surface of FeSe.Comment: Latex, 5 pages, 4 figure