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Evolution of the SrTiO 3 surface electronic state as a function of LaAlO 3 overlayer thickness

2017; Elsevier BV; Volume: 412; Linguagem: Inglês

10.1016/j.apsusc.2017.03.208

1873-5584

N. C. Plumb, Michio Kobayashi, M. Salluzzo, E. Razzoli, C. E. Matt, V. N. Strocov, Ke‐Jin Zhou, M. Shi, J. Mesot, Thorsten Schmitt, L. Patthey, M. Radović,

Advanced X-ray and CT Imaging

The novel electronic properties emerging at interfaces between transition metal oxides, and in particular the discovery of conductivity in heterostructures composed of LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) band insulators, have generated new challenges and opportunities in condensed matter physics. Although the interface conductivity is stabilized when LAO matches or exceeds a critical thickness of 4 unit cells (u.c.), other phenomena such as a universal metallic state found on the bare surface of STO single crystals and persistent photon-triggered conductivity in otherwise insulating STO-based interfaces raise important questions about the role of the LAO overlayer and the possible relations between vacuum/STO and LAO/STO interfaces. Here, we study how the metallic STO surface state evolves using angle-resolved photoemission spectroscopy (ARPES) in situ prepared samples complemented by resonant inelastic X-ray scattering (RIXS) during the growth of a crystalline LAO overlayer. In all the studied samples, the character of the conduction bands, their carrier densities, the Ti3+ crystal field, and the response to photon irradiation bear strong similarities. Nevertheless, we report here that studied LAO/STO interfaces exhibit an instability toward an apparent 2 x 1 folding of the Fermi surface at and above 4 u.c. thickness threshold, which distinguishes these heterostructures from bare STO and sub-critical-thickness LAO/STO.