Hard x-ray angle-resolved photoemission from a buried high-mobility electron system

M. Zapf, M. Schmitt, J. Gabel, P. Scheiderer, M. Stübinger, B. Leikert, G. Sangiovanni, L. Dudy, S. Chernov, S. Babenkov, D. Vasilyev, O. Fedchenko, K. Medjanik, Y. Matveyev, A. Gloskowski, C. Schlueter, T. Lee, H. Elmers, G. Schönhense, M. Sing, and R. Claessen

Abstract

Novel two-dimensional electron systems at the interfaces and surfaces of transition-metal oxides recently have attracted much attention as they display tunable, intriguing properties that can be exploited in future electronic devices. Here we show that a high-mobility quasi-two-dimensional electron system with strong spin-orbit coupling can be induced at the surface of a KTaO3 (001) crystal by pulsed laser deposition of a disordered LaAlO3 film. The momentum-resolved electronic structure of the buried electron system is mapped out by hard x-ray angle-resolved photoelectron spectroscopy. From a comparison to calculations, it is found that the band structure deviates from that of electron-doped bulk KTaO3 due to the confinement to the interface. Fermi surface mapping shows a three-dimensional, periodic intensity pattern consistent with electron pockets of quantum well states centered around the Γ points and the expectations from a Fourier analysis-based description of photoemission on confined electron systems. From the k broadening of the Fermi surface and core-level depth profiling, we estimate the extension of the electron system to be at least 1 nm but not much larger than 2 nm, respectively.

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