Coexistence of surface oxygen vacancy and interface conducting states in LaAlO3/SrTiO3 revealed by grazing-angle resonant soft x-ray scattering

• Published in: Applied physics reviews 2023-06, Vol.10 (2)
• Main Authors: Yang, Ming, Ariando, Ariando, Diao, Caozheng, Lee, James C., Jayaraman, Kaushik, Jalil, Mansoor B. A., Smadici, Serban, Zeng, Shengwei, Zhou, Jun, Kong, Weilong, Breese, Mark B. H., Dhar, Sankar, Feng, Yuan Ping, Abbamonte, Peter, Venkatesan, Thirumalai, Rusydi, Andrivo
• Format: Article
• Language: English
• ISSN: 1931-9401; 1931-9401
• DOI: 10.1063/5.0132786

Oxide heterostructures have shown rich physics phenomena, particularly in the conjunction of exotic insulator–metal transition (IMT) at the interface between polar insulator LaAlO3 and non-polar insulator SrTiO3 (LaAlO3/SrTiO3). The polarization catastrophe model has suggested an electronic reconstruction, yielding to metallicity at both the interface and surface. Another scenario is the occurrence of surface oxygen vacancy at LaAlO3 (surface-Ov), which has predicted surface-to-interface charge transfer, yielding metallic interface but insulating surface. To clarify the origin of IMT, one should probe surface-Ov and the associated electronic structures at both the surface and the buried interface simultaneously. Here, using grazing-angle resonant soft x-ray scattering (GA-RSXS) supported with first-principles calculations, we reveal the co-existence of the surface-Ov state and the interface conducting state only in conducting LaAlO3/SrTiO3 (001) films. Interestingly, both the surface-Ov state and the interface conducting state are absent for the insulating film. As a function of Ov density, while the surface-Ov state is responsible for the IMT, the spatial charge distribution is found responsible for a transition from two-dimensional-like to three-dimensional-like conductivity accompanied by spectral weight transfer, revealing the importance of electronic correlation. Our results show the importance of surface-Ov in determining interface properties and provide a new strategy in utilizing GA-RSXS to directly probe the surface and buried interface electronic properties in complex oxide heterostructures.