High mobility electron gas in the surface vicinity of the cubic-perovskite KTaO$_3$ via Ar$^+$-irradiation

KTaO$_{3}$ (KTO), like SrTiO$_{3}$ (STO), can be doped to create a high mobility perovskite oxide semiconductor. However, while the low dimensional electronic states of STO have attracted intense interest via spectroscopic [1,2] and transport [3] studies, analogous investigations in KTO have been limited. Of particular interest is the fact that the cubic crystal symmetry in KTO is preserved at low temperatures, in contrast to STO. Here we electron dope KTO via oxygen-vacancy formation by Ar$^+$-irradiation [4]. Below $T$ = 10 K, the Hall mobility ($>$ 10$^4$ cm$^2$/Vs) of the electrons is significantly higher than in previous studies of STO [4]. The angular dependence of the Shubnikov-de Haas oscillations indicates a Fermi surface without cubic symmetry, in contrast to that expected for bulk KTO. We discuss the possible origins of these data, including the formation of quantum well structures, the coexistence of surface and bulk electrons, and the suppression of cyclotron motion by finite size effects.\\[4pt] [1] A. F. Santander-Syro \textit{et al}., Nature \textbf{469}, 189 (2011).\\[0pt] [2] W. Meevasana \textit{et al}., Nat. Mater. \textbf{10}, 114 (2011).\\[0pt] [3] Y. Kozuka \textit{et al}., Nature \textbf{462}, 487 (2009).\\[0pt] [4] J. H. Ngai \textit{et al.}, Phys. Rev. B \textbf{81}, 241307 (2010).