Orbital Edelstein effect in topological insulators

We theoretically propose a gigantic orbital Edelstein effect in topological insulators and interpret the results in terms of topological surface currents. We numerically calculate the orbital Edelstein effect for a model of a three-dimensional Chern insulator as an example. Furthermore, we calculate the orbital Edelstein effect as a surface quantity using a surface Hamiltonian of a topological insulator, and numerically show that it well describes the results by direct numerical calculation. We find that the orbital Edelstein effect depends on the local crystal structure of the surface, which shows that the orbital Edelstein effect cannot be defined as a bulk quantity. We propose that Chern insulators and Z2 topological insulators can be a platform with a large orbital Edelstein effect because current flows only along the surface. We also propose candidate topological insulators for this effect. As a result, the orbital magnetization as a response to the current is much larger in topological insulators than that in metals by many orders of magnitude.

Effect of processing on the structures and properties of bismuth sodium titanate compounds

The processing of sodium (Na) and bismuth (Bi)-based piezoelectric compounds are always a concern due to their volatilization at high temperatures (> 1000 °C) and the hygroscopic nature of the precursors. The effect of drying and impurities in the precursors on 0.94(Bi0.5Na0.5TiO3)–0.06BaTiO3 (BNTBT) ceramics was investigated. A substantial difference in the weight fraction of polar (R3c) and weak-polar (P4bm) phase at room temperature was observed for BNTBT obtained from dried, undried and low purity precursors, evaluated by XRD and Raman. The local crystal structure was evaluated by transmission electron microscope, which showed the presence of both ferroelectric domains and polar nano regions. The electrical measurements corroborated well with the structure results, and showed a variation in the depolarization temperature (Td). The results highlight the importance of the pre-processing steps on the functional compounds obtained from sensitive elements, which has broader implementations for similar systems.

Tuning the upconversion luminescence of cubic KMnF3:Yb3+/Er3+ nanocrystals through inert lanthanide ion doping

Efficient tailoring of upconversion emissions in conventional single red emitting KMnF3:Yb3+/Er3+ nanocrystals is achieved through local crystal structure engineering and the suppression of energy transfer as well as back transfer, which is of great significance for extended optical applications.