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  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.M.; Geck, J.: Transition from a uni- to a bimodal interfacial charge distribution in LaAlO₃/SrTiO₃ upon cooling. Scientific Reports 10 (2020), p. 18359 /1-10

10.1038/s41598-020-74364-7
Open Accesn Version

Abstract:
We present a combined resonant soft X-ray reflectivity and electric transport study of LaAlO3/SrTiO3 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 LaAlO3/SrTiO3 interface. At room temperature the corresponding electrons are located close to the interface, extending down to 4 unit cells into the SrTiO3 substrate. Upon cooling, however, these interface electrons assume a bimodal depth distribution: They spread out deeper into the SrTiO3 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 LaAlO3 film and support the notion of a complex interplay between structural and electronic degrees of freedom.