The synthesis of materials with well-controlled composition and structure improves our understanding of their intrinsic electrical transport properties. Recent developments in atomically controlled growth have been shown to be crucial in enabling the study of new physical phenomena in epitaxial oxide heterostructures. Nevertheless, these phenomena can be infl uenced by the presence of defects that act as extrinsic sources of both doping and impurity scattering. Control over the nature and density of such defects is therefore necessary to fully understand the intrinsic materials properties and exploit them in future device technologies. Here, it is shown that incorporation of a strontium copper oxide nano-layer strongly reduces the impurity scattering at conducting interfaces in oxide LaAlO 3 -SrTiO 3 (001) heterostructures, opening the door to high carrier mobility materials. It is proposed that this remote cuprate layer facilitates enhanced suppression of oxygen defects by reducing the kinetic barrier for oxygen exchange in the hetero-interfacial fi lm system. This design concept of controlled defect engineering can be of signifi cant importance in applications in which enhanced oxygen surface exchange plays a crucial role.

We have performed high field magnetotransport measurements to investigate the interface electron gas in a high mobility SrTiO3/SrCuO2/LaAlO3/SrTiO3 heterostructure. Shubnikov-de Haas oscillations reveal several 2D conduction subbands with carrier effective masses of 0.9me and 2me, quantum mobilities of order 2000 cm2/V s, and band edges only a few millielectronvolts below the Fermi energy. Measurements in tilted magnetic fields confirm the 2D character of the electron gas, and show evidence of inter-subband scattering.

Hard x-ray photoemission and density functional theory study of the internal electric field in SrTiO3/LaAlO3 oxide heterostructures Slooten, E.; Zhong, Z.; Molegraaf, H.J.A.; Eerkes, P.D.; de Jong, S.; Massee, F.; van Heumen, E.; Kruize, M.K.; Wenderich, S.; Kleibeuker, J.E.; Gorgoi, M.; Hilgenkamp, H.; Brinkman, A.; Huijben, M; Rijnders, G.; Blank, D.H.A.; Koster, G.; Kelly, P.J.; Golden, M.S. Published in:Physical Review B DOI:10.1103/PhysRevB.87.085128 Link to publicationCitation for published version (APA): Slooten, E., Zhong, Z., Molegraaf, H. J. A., Eerkes, P. D., de Jong, S., Massee, F., ... Golden, M. (2013). Hard xray photoemission and density functional theory study of the internal electric field in SrTiO3/LaAlO3 oxide heterostructures. Physical Review B, 87(8), 085128. https://doi.org/10.1103/PhysRevB.87.085128 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. A combined experimental and theoretical investigation of the electronic structure of the archetypal oxide heterointerface system LaAlO 3 on SrTiO 3 is presented. High-resolution, hard x-ray photoemission is used to uncover the occupation of Ti 3d states and the relative energetic alignment-and hence internal electric fields-within the LaAlO 3 layer. First, the Ti 2p core-level spectra clearly show occupation of Ti 3d states already for two unit cells of LaAlO 3 . Second, the LaAlO 3 core levels were seen to shift to lower binding energy as the LaAlO 3 overlayer thickness, n, was increased, agreeing with the expectations from the canonical electron transfer model for the emergence of conductivity at the interface. However, not only is the energy offset of only ∼300 meV between n = 2 (insulating interface) and n = 6 (metallic interface) an order of magnitude smaller than the simple expectation, but it is also clearly not the sum of a series of unit-cell-by-unit-cell shifts within the LaAlO 3 block. Both of these facts argue against the simple charge-transfer picture involving a cumulative shift of the LaAlO 3 valence bands above the SrTiO 3 conduction bands, resulting in charge transfer only for n 4. We discuss effects which could frustrate this elegant and simple charge-transfer model, concluding that although it cannot be ruled out, photodoping by the x-ray beam is unlikely to be the cause of the o...

The low-temperature resistance of a conducting LaAlO 3 /SrTiO 3 interface with a 10 nm thick LaAlO 3 film decreases by more than 50% after illumination with light of energy higher than the SrTiO 3 band-gap. We explain our observations by optical excitation of an additional high mobility electron channel, which is spatially separated from the photo-excited holes. After illumination, we measure a strongly non-linear Hall resistance which is governed by the concentration and mobility of the photo-excited carriers. This can be explained within a two-carrier model where illumination creates a high-mobility electron channel in addition to a lowmobility electron channel which exists before illumination. 9-11 Several mechanisms are suggested to describe the origin of conductivity at the LAO/STO interface.12-17 However, the relative contribution of each mechanism strongly depends on the LAO film thickness and on the LAO growth conditions such as substrate temperature, oxygen partial pressure and the post annealing treatment.18 In particular, growing 5-10 layers of LAO on STO yields a metallic interface with relatively high mobility and low electron concentration, 19,20 whereas growing 26 LAO layers with the same conditions results in a low mobility, high concentration electron system with interesting magnetic properties.3 Tuning the transport properties at such a complex oxide interface by modulating the carrier density with light can both contribute to the understanding of its physics and open new pathways towards oxide-based optoelectronic device applications. It has been shown previously that interface conductivity in oxide heterostructures can be tuned by light or by an electric field. 21-23In this Letter we report our investigation of the interface of a LAO/STO sample with 26 monolayers of LAO, using low-temperature (4.2 K) magnetotransport experiments under selective illumination. Illuminating the sample with UV light of energy greater than the STO band gap results in a sharp and persistent decrease of electrical resistance. Using Hall effect measurements, we show that before illumination there is a single, low mobility electron conduction band, and that the resistance drop on illumination can be explained by the creation of a parallel conducting channel containing optically excited a) Electronic mail: u.zeitler@science.ru.nl high mobility electrons.Our sample was grown by pulsed laser deposition and has a 10 nm thick (26 unit cells) LAO film on a TiO 2 -terminated single crystal STO [001] substrate (treatment described in Ref. 24). The LAO film was deposited at a substrate temperature of 850• C and an oxygen pressure of 2 × 10 −3 mbar, using a single-crystal LaAlO 3 target. The growth of the LAO film was monitored using in situ reflection high-energy electron diffraction. After the growth, samples were cooled to room temperature in the deposition pressure.The sample was mounted on a ceramic chip carrier and electrical contacts were made with an ultrasonic wirebonder, using aluminium wires. The magnetoresistance an...

We have measured the Hall resistance and magneto-resistance (MR) of LaAlO3/SrTiO3 heterojunctions at magnetic fields up to 30 T in a temperature range T = 4 K to 70 K. For temperature below 7 K and above 50 K the devices display linear Hall resistance, indicating that one type of charge carriers dominate the transport. For temperatures between 10 K and 40 K, the Hall resistance is strongly non-linear, and is accompanied by a large positive MR, which is governed by the component of magnetic field normal to the interface. This behaviour in the intermediate temperature regime can be related to thermally activated high-mobility carriers.