Spring Meeting 2015 in Berlin

Iron-pnictides Ca(Fe1-xRhx)2As2 (x = 0, 0.035 and 0.19) were studied across the tetragonal-orthorhombic and tetragonal collapsed tetragonal phase transitions using Raman spectroscopy. Effects of phase separation were observed in the high-temperature phase for the first time. An orbital order scenario at low temperatures for the Rh doped samples which requires a symmetry lowering down to P4/mnc or I422 without atomic displacements relative to the parent I4/mmm symmetry is discussed. Work supported by RTG-DFG 1953/1, Metrology for Complex Nanosystems.

Inelastic light scattering studies on single crystals of (Na1−xLix)2(Ir1−yTiy)O3 (x = 0, 0.1, 0.2; y = 0, 0.025) show a polarization and temperature dependent broad band as well as phonon anomalies. We discuss these observations with respect to the relevance of the Kitaev-Heisenberg model and Majorana Fermions for A2IrO3. Work supported by RTG-DFG 1953/1, Metrology for Complex Nanosystems.

The search for topologically stable vortex-like objects (Skyrmions) in insulating chiral magnets lead to their discovery in Cu2OSeO3 [1]. We will show that the combination of certain structural features, such as chirality and frustration might expedite the finding of new candidates of this rare class. A chiral paddle-wheel type of structure featuring geometric frustration has been reported for the metrically cubic title compound with ferrimagnetic, Tc=18 K, and dielectric anomalies [2]. Interestingly, Raman scattering shows magnetoelastic coupling of several phonons but no spontaneous symmetry reduction. This is considered a prerequisite for the existence of a Skyrmion lattice. This work was supported by the NSF (DMR-1149899) and RTG-DFG 1953/1.

In the symmetry-broken topological Dirac semimetal with strong spin-orbit coupling, Cd3As2, a pronounced temperature evolution of quasielastic electronic Raman scattering and resonant effects are observed. These effects are then compared to observations in topological insulators, as Bi2Se3. Work supported by RTG-DFG 1953/1, Metrology for Complex Nanosystems and the Laboratory for Emerging Nanometrology Braunschweig, TU Braunschweig.

ZnO coated TiO2 photoanodes for cost efficient dye sensitized solar cells are prepared using anodization of a metal electrode leading to an array of TiO2 nanotubes. Atomic layer deposition is used for the conformal covering by ZnO. Following hematoporphyrin sensitization the improved electron transfer is probed using time resolved fluorescence. Work supported by RTG-DFG 1953/1, Metrology for Complex Nanosystems and the Laboratory for Emerging Nanometrology, TU Braunschweig.