Insulating SrTiO3 (STO) can host 2D electron systems (2DESs) on its surfaces, caused by oxygen defects. This study shows that the STO surface exhibits phase separation once the 2DES is formed and relates this inhomogeneity to recently reported magnetic order at STO surfaces and interfaces. The results open pathways to exploit oxygen defects for engineering the electronic and magnetic properties of oxides.

The Mott transistor is a paradigm for a new class of electronic devices-often referred to by the term Mottronics-which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal-insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band-filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO thin films making it a promising channel material in future Mottronic devices.

No abstract

The spinel/perovskite heterointerface γ-Al2O3/SrTiO3 hosts a two-dimensional electron system (2DES) with electron mobilities exceeding those in its all-perovskite counterpart LaAlO3/SrTiO3 by more than an order of magnitude despite the abundance of oxygen vacancies which act as electron donors as well as scattering sites. By means of resonant soft x-ray photoemission spectroscopy and ab initio calculations we reveal the presence of a sharply localized type of oxygen vacancies at the very interface due to the local breaking of the perovskite symmetry. We explain the extraordinarily high mobilities by reduced scattering resulting from the preferential formation of interfacial oxygen vacancies and spatial separation of the resulting 2DES in deeper SrTiO3 layers. Our findings comply with transport studies and pave the way towards defect engineering at interfaces of oxides with different crystal structures.The search for high-mobility two-dimensional electron systems (2DES) at atomically engineered transition metal oxide heterointerfaces is an ongoing endeavor, since the strong electronic correlations in partially occupied d-orbitals promise an even richer physical behavior than found in conventional semiconductor heterostructures [1]. However, the charge carrier mobilities in the most prominent complex oxide 2DES, found at the perovskite-perovskite heterointerface between the band insulators LaAlO 3 and SrTiO 3 , still fall short of those in semiconductors by several orders of magnitude [2]. The hitherto-highest mobility in SrTiO 3 -based structures (140,000 cm 2 /Vs at 2 K) is found at the spinel/perovskite heterointerface between γ-Al 2 O 3 thin films and SrTiO 3 [3, 4], thus making it a promising candidate for applications in oxide electronics or fundamental studies of quantum transport. The mechanism of 2DES formation in SrTiO 3 -based heterostructures has been under debate for many years.

No abstract