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- ItemCorrelation induced electron-hole asymmetry in quasi- two-dimensional iridates(London : Nature Publishing Group, 2017) Pärschke, E.M.; Wohlfeld, K.; Foyevtsova, K.; Van Den Brink, J.The resemblance of crystallographic and magnetic structures of the quasi-two-dimensional iridates Ba2IrO4 and Sr2IrO4 to La2CuO4 points at an analogy to cuprate high-Tc superconductors, even if spin-orbit coupling is very strong in iridates. Here we examine this analogy for the motion of a charge (hole or electron) added to the antiferromagnetic ground state. We show that correlation effects render the hole and electron case in iridates very different. An added electron forms a spin polaron, similar to the cuprates, but the situation of a removed electron is far more complex. Many-body 5d 4 configurations form which can be singlet and triplet states of total angular momentum that strongly affect the hole motion. This not only has ramifications for the interpretation of (inverse-)photoemission experiments but also demonstrates that correlation physics renders electron- and hole-doped iridates fundamentally different.
- ItemTwo types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1 +yTe(Washington : National Academy of Sciences, 2019) Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U.K.; Wirth, S.A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state.
- ItemRevealing orbital and magnetic phase transitions in Pr0.5Ca0.5MnO3 epitaxial thin films by resonant soft x-ray scattering(Milton Park : Taylor & Francis, 2014) Wadati, H.; Geck, J.; Schierle, E.; Sutarto, R.; He, F.-J.; Hawthorn, D.G.; Nakamura, M.; Kawasaki, M.; Tokura, Y.; Sawatzky, G.A.Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine theminimum-energy out-of-plane lattice parameter, cmin (a, b).We showbymeans of density-functional total energy calculations that this dependence can be discontinuous and predict related firstorder phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of cmin can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of cmin.
- ItemPrediction of first-order martensitic transitions in strained epitaxial films(Milton Park : Taylor & Francis, 2015) Schönecke, S.; Richter, M.; Koepernik, K.; Eschrig, H.Coherent epitaxial growth allows us to produce strained crystalline films with structures that are unstable in the bulk. Thereby, the overlayer lattice parameters in the interface plane, (a, b), determine theminimum-energy out-of-plane lattice parameter, cmin (a, b).We showbymeans of density-functional total energy calculations that this dependence can be discontinuous and predict related firstorder phase transitions in strained tetragonal films of the elements V, Nb, Ru, La, Os, and Ir. The abrupt change of cmin can be exploited to switch properties specific to the overlayer material. This is demonstrated for the example of the superconducting critical temperature of a vanadium film which we predict to jump by 20% at a discontinuity of cmin.
- ItemCrystal structure of (1S, 2R,4S)-1-((phenylamino)methyl)-4-(prop-1-en-2-yl) cyclohexane-1,2-diol), C16H23NO2(Heidelberg : Springer, 2011) Outouch, R.; Boualy, B.; El Firdoussi, L.; Ali, M.A.; Rizzoli, C.; Spannenberg, A.C16H23NO2, orthorhombic, P2 12121 (no. 19), a = 5.9637(3) Å, b = 8.8317(5) Å, c = 27.809(1) Å, V = 1464.7 Å3, Z = 4, Rgt(F) = 0.026, wRref(F2) = 0.040, T= 150 K.