物構研談話会（17-03）

概要

Low-dimensional electron transport observed along complex oxide heterointerfaces has attracted enormous attention in recent years. While the formation of these 2-dimensional electron gases is generally attributed to electronic charge transfer triggered by a built-in electric field, the ionic defect structure at these interfaces is still being discussed controversially.

Here, we address the thermodynamic processes associated with built-in electric fields and derive ionic defect concentration profiles established at polar/non-polar oxide interfaces. [1] As we discuss, the specific ionic-electronic defect structure stabilized within such interfacial space charge layers strongly depends on ambient oxygen partial pressure applied during sample fabrication and on the strength of the built-in electric field.

As we ground states obtained for various oxide heterostructure systems [2] and discuss resulting implications for important measures characterizing the electron gas, such as electron mobility [3] as well as its magnetic signature [4], both controllable by thermodynamic means. The thermodynamic model obtained for oxide heterointerfaces is furthermore linked to kinetic space charge formation occurring at complex oxide surfaces [5, 6].

[1] F. Gunkel et al., "Defect concentration profiles at complex oxide interfaces", Physical Review B 93, 245431 (2016)

[2] F. Gunkel et al., "Thermodynamic ground states of complex oxide heterointerfaces", ACS Applied Materials & interfaces, ACS Appl. Mater. Interfaces, 9 (1), 1086 (2017)

[3] C. Xu et al., "Disentanglement of growth dynamic and thermodynamic effects in LaAlO3/SrTiO3 heterostructures", Scientific Reports 6, 22410 (2016)

[4] F. Gunkel, et al., "Defect-control of anomalous and conventional electron transport in NdGaO3/SrTiO3 heterostructures", Physical Review X, 6, 031035 (2016)

[5] R. Meyer et al., "Dynamics of the metal-insulator transition of donor-doped SrTiO3", Physical Review B 94, 115408 (2016)

[6] M. Andrae et al., "Oxygen partial pressure dependence of surface space charge formation in donor-doped SrTiO3", APL Materials 5, 056106 (2017)