Band-Order Anomaly at the γ-Al2O3/SrTiO3 Interface Drives the Electron-Mobility Boost

Abstract

Rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about two orders of magnitude has been demonstrated at the spinel/perovskite γ-Al2O3/SrTiO3 interface compared to the paradigm perovskite/perovskite LaAlO3/SrTiO3. We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in γ-Al2O3/SrTiO3 which depopulates electron states in the top STO layer. This rearrangement of the mobile electron system pushes the electron density away from the interface that reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel γ-Al2O3 and perovskite SrTiO3. The band-order engineering exploiting the fundamental symmetry properties emerges as another route to boost the performance of oxide devices.

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Cited by in corpus (7)

• Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO${}_3$ interfaces
• Interface properties of CsPbBr${}_3$ /CsPbI${}_3$ perovskite heterostructure for solar cell
• Electronic band structure of Ti2O3 thin films studied by angle-resolved photoemission spectroscopy
• High-mobility two-dimensional electron gas in $\gamma$-Al${}_2$O${}_3$/SrTiO${}_3$ heterostructures
• Quantum oscillations in an optically-illuminated two-dimensional electron system at the LaAlO${}_3$/SrTiO${}_3$ interface
• Coexistence of high electron-mobility, unpaired spins, and superconductivity at high carrier density SrTiO${}_3$-based interfaces
• Leveraging high fluence and low pressure for pulsed laser deposition of high-mobility $\gamma$-Al${}_2$O${}_3$/SrTiO${}_3$ heterostructure growth