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

TL;DR

This study demonstrates the induction and characterization of a high-mobility, spin-orbit coupled two-dimensional electron system at the surface of KTaO3 using hard x-ray ARPES, revealing a confined, three-dimensional Fermi surface.

Contribution

It introduces a method to create and analyze a high-mobility electron system at oxide interfaces with detailed electronic structure mapping.

Findings

High-mobility electron system induced at KTaO3 surface

Fermi surface is three-dimensional despite confinement

Electron system extends 1-2 nm from surface

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 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.