The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. Herein we show that metallic interfaces can be realized in SrTiO 3 -based heterostructures with various insulating overlayers of amorphous LaAlO 3 , SrTiO 3 and yttria-stabilized zirconia films. On the other hand, samples of amorphous La 7/8 Sr 1/8 MnO 3 films on SrTiO 3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of SrTiO 3 substrates play an important role.

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO 3 and SrTiO 3 , provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much beyond the current value of approximately 1,000 cm 2 V -1 s -1 (at low temperatures). Here we create a new type of two-dimensional electron gas at the heterointerface between SrTiO 3 and a spinel g-Al 2 O 3 epitaxial film with compatible oxygen ions sublattices. Electron mobilities more than one order of magnitude higher than those of hitherto-investigated perovskite-type interfaces are obtained. The spinel/perovskite twodimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface. Our findings pave the way for studies of mesoscopic physics with complex oxides and design of high-mobility all-oxide electronic devices.

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Document VersionEarly version, also known as pre-print Link back to DTU Orbit Citation (APA):Chen, Y., Trier, F., Wijnands, T., Green, R. J., Gauquelin, N., Egoavil, R., ... Pryds, N. (2015). Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces via charge transfer induced modulation doping. Nature Materials, 14(8) Supplementary Information, Fig. S1). For all samples, with the d-LAO film thickness up to 20 nm, atomic force microscopy (AFM) images show regular surface terraces with a step height of 0.4 nm (Fig. 1b), similar to that of the original STO substrate and indicating uniform film growth. Representative samples were investigated further by scanning transmission electron microscopy (STEM). Our subsequent spectroscopic measurements reveal dramatic electronic reconstruction in the LSMO-buffered samples. Firstly, different from the unbuffered d-LAO/STO sample where the 2DEG is coupled strongly to a large content of oxygen vacancies extending more than 3 nm deep into STO 24 , all buffered samples show a rather low content of Ti 3+ far below the detection limit of our in situ X-ray photoelectron