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- 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.
- ItemTransition from a uni- to a bimodal interfacial charge distribution in LaAlO 3 / SrTiO 3 upon cooling([London] : Macmillan Publishers Limited, part of Springer Nature, 2020) Zwiebler, M.; Di Gennaro, E.; Hamann-Borrero, J.E.; Ritschel, T.; Green, R.J.; Sawatzky, G.A.; Schierle, E.; Weschke, E.; Leo, A.; Granozio, F. Miletto; Geck, J.We present a combined resonant soft X-ray reflectivity and electric transport study of LaAlO 3/SrTiO 3 field effect devices. The depth profiles with atomic layer resolution that are obtained from the resonant reflectivity reveal a pronounced temperature dependence of the two-dimensional electron liquid at the LaAlO 3/SrTiO 3 interface. At room temperature the corresponding electrons are located close to the interface, extending down to 4 unit cells into the SrTiO 3 substrate. Upon cooling, however, these interface electrons assume a bimodal depth distribution: They spread out deeper into the SrTiO 3 and split into two distinct parts, namely one close to the interface with a thickness of about 4 unit cells and another centered around 9 unit cells from the interface. The results are consistent with theoretical predictions based on oxygen vacancies at the surface of the LaAlO 3 film and support the notion of a complex interplay between structural and electronic degrees of freedom. © 2020, The Author(s).