Alla Chikina
Leibniz Institute for Solid State Research, IFW Dresden, D-01171 Dresden, Germany

Photoemission insight into the electronic properties of oxide interfaces

Abstract:

Interfacing transition metal generates the huge potential for achieving new physical properties tuning the interplay of electron, spin, orbital and lattice degrees of freedom. Indeed, the two-dimensional electron system (2DES) emergent at the interface between two wide band-gap insulators LaAlO₃ (LAO) and SrTiO₃ (STO) has opened new perspectives of oxide electronics.  Oxygen vacancies (V_Os) play an important role in the electronic and magnetic properties of this interface due to the formation of a dichotomic electron system where strongly correlated localized electrons in the in-gap states (IGSs) coexist with less correlated ones constituting the mobile two-dimensional electron system (2DES)¹.

Using resonant soft-X-ray ARPES experiments at the ADRESS beamline of Swiss Light Source, we establish orbital character of the mobile and localized electron states at the LAO/STO interface created by the V_Os. We identify the predominantly Ti e_g- vs t_2g-derived orbital character of these two electron systems. Furthermore, we have distinguished different chemical states of the in-gap electrons and an additional crosstalk between the localized and mobile electron systems².

Since V_Os releases electrons to the system and, at the same time, assist increase the defect scattering rate, the separation of doped electrons and the source of doping can considerably increase the mobility of the system³. We consider this effect on the example of ?-Al₂O₃/STO, focusing on the unique band structure and carriers scattering on the V_Os.

In the end, we provide fundamental understanding of X-ray induced oxygen migration at the STO-based interfaces. The controlled redox reaction results in formation of the interfacial metallicity which stays stable at ambient conditions. Our discovery of the X-ray pattering for the STO-based interfaces offers a technology of stable charge patterning for future oxide-based electronic devices.

[1]  F. Lechermann et al., Physical Review B 90, 85125 (2014).

[2] A. Chikina et al., ACS Nano 12, 7927–7935 (2018).

[3] C. Cancellieri et al., Nature Communications 7, 10386 (2016).