  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
KTaO$_3$ (001) crystal by pulsed laser deposition of a disordered LaAlO$_3$
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 KTaO$_3$ due to the confinement to the interface.
Nevertheless, the Fermi surface appears to be clearly three-dimensional. 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.
