Growth-induced electron mobility enhancement at the LaAlO3_3/SrTiO3_3 interface

We have studied the electronic properties of the 2D electron liquid present at the LaAlO$_3$/SrTiO$_3$ interface in series of samples prepared at different growth temperatures. We observe that interfaces fabricated at 650{\deg}C exhibit the highest low temperature mobility ($\approx 10000 \textrm{ cm}^2/\textrm{Vs}$) and the lowest sheet carrier density ($\approx 5\times 10^{12} \textrm{ cm}^{-2}$). These samples show metallic behavior and Shubnikov-de Haas oscillations in their magnetoresistance. Samples grown at higher temperatures (800-900{\deg}C) display carrier densities in the range of $\approx 2-5 \times 10^{13} \textrm{ cm}^{-2}$ and mobilities of $\approx 1000 \textrm{ cm}^2/\textrm{Vs}$ at 4K. Reducing their carrier density by field effect to $8\times 10^{12} \textrm{ cm}^{-2}$ lowers their mobilites to $\approx 50 \textrm{ cm}^2/\textrm{Vs}$ bringing the conductance to the weak-localization regime

Tunable Rashba spin-orbit interaction at oxide interfaces

The quasi-two-dimensional electron gas found at the LaAlO3/SrTiO3 interface offers exciting new functionalities, such as tunable superconductivity, and has been proposed as a new nanoelectronics fabrication platform. Here we lay out a new example of an electronic property arising from the interfacial breaking of inversion symmetry, namely a large Rashba spin-orbit interaction, whose magnitude can be modulated by the application of an external electric field. By means of magnetotransport experiments we explore the evolution of the spin-orbit coupling across the phase diagram of the system. We uncover a steep rise in Rashba interaction occurring around the doping level where a quantum critical point separates the insulating and superconducting ground states of the system

Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures

Obtaining high-quality thin films of 5d transition metal oxides is essential to explore the exotic semimetallic and topological phases predicted to arise from the combination of strong electron correlations and spin-orbit coupling. Here, we show that the transport properties of SrIrO3 thin films, grown by pulsed laser deposition, can be optimized by considering the effect of laser-induced modification of the SrIrO3 target surface. We further demonstrate that bare SrIrO3 thin films are subject to degradation in air and are highly sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited in-situ is effective in preserving the film quality, allowing us to measure metallic transport behavior in films with thicknesses down to 4 unit cells. In addition, the SrTiO3 encapsulation enables the fabrication of devices such as Hall bars without altering the film properties, allowing precise (magneto)transport measurements on micro- and nanoscale devices.Comment: 5 pages, 3 figure

Seebeck effect in the conducting LaAlO_{3}/SrTiO_{3} interface

The observation of metallic behavior at the interface between insulating oxides has triggered worldwide efforts to shed light on the physics of these systems and clarify some still open issues, among which the dimensional character of the conducting system. In order to address this issue, we measure electrical transport (Seebeck effect, Hall effect and conductivity) in LaAlO_{3}/SrTiO_{3} interfaces and, for comparison, in a doped SrTiO_{3} bulk single crystal. In these experiments, the carrier concentration is tuned, using the field effect in a back gate geometry. The combined analysis of all experimental data at 77 K indicates that the thickness of the conducting layer is ~7 nm and that the Seebeck effect data are well described by a two-dimensional (2D) density of states. We find that the back gate voltage is effective in varying not only the charge density, but also the thickness of the conducting layer, which is found to change by a factor of ~2, using an electric field between -4 and +4MV/m at 77K. No enhancement of the Seebeck effect due to the electronic confinement and no evidence for two-dimensional quantization steps are observed at the interfaces.Comment: 15 pages, 5 figure

Superconductivity at the LaAlO3/SrTiO3interface

We report on the structural characterization of LaAlO3/SrTiO3 interfaces and on their transport properties. LaAlO3 films were prepared using pulsed laser deposition onto TiO2 terminated (001) SrTiO3 substrates inducing a metallic conduction at the interface. Resistance and Hall effect measurements reveal a sheet carrier density between 0.4 and 1.2·10 14 electrons/cm 2 at room temperature and mobility of ∼ 300 cm 2 V −1 s −1 at low temperatures. A transition to a superconducting state is observed at a temperature of ∼ 200 mK. The superconducting characteristics display signatures of 2D superconductivity

Diodes with Breakdown Voltages Enhanced by the Metal-Insulator Transition of LaAlO3_3-SrTiO3_3 Interfaces

Using the metal-insulator transition that takes place as a function of carrier density at the LaAlO$_3$-SrTiO$_3$ interface, oxide diodes have been fabricated with room-temperature breakdown voltages of up to 200 V. With applied voltage, the capacitance of the diodes changes by a factor of 150. The diodes are robust and operate at temperatures up to 270 C

Two-dimensional superconductivity at the (111)LaAlO3_3/SrTiO3_3 interface

We report on the discovery and transport study of the superconducting ground state present at the (111)LaAlO$_3$/SrTiO$_3$ interface. The superconducting transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and its 2D nature is further corroborated by the anisotropy of the critical magnetic field, as calculated by Tinkham. The estimated superconducting layer thickness and coherence length are 10 nm and 60 nm, respectively. The results of this work provide a new platform to clarify the microscopic details of superconductivity at LaAlO$_3$/SrTiO$_3$ interfaces, in particular in what concerns the link with orbital symmetry.Comment: 4 pages, 4 figure

Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces

We report on a study of magnetotransport in LaAlO3/SrTiO3 interfaces characterized by mobilities of the order of several thousands cm$^{2}$/Vs. We observe Shubnikov-de Haas oscillations that indicate a two-dimensional character of the Fermi surface. The frequency of the oscillations signals a multiple sub-bands occupation in the quantum well or a multiple valley configuration. From the temperature dependence of the oscillation amplitude we extract an effective carrier mass $m^{*}\simeq1.45$\,$m_{e}$. An electric field applied in the back-gate geometry increases the mobility, the carrier density and the oscillation frequency.Comment: 4 pages, 4 figure

Electrostatically tuned quantum superconductor-metal-insulator transition at the LaAlO3/SrTiO3 interface

Recently superconductivity at the interface between the insulators LaAlO3 and SrTiO3 has been tuned with the electric field effect to an unprecedented range of transition temperatures. Here we perform a detailed finite size scaling analysis to explore the compatibility of the phase transition line with Berezinskii-Kosterlitz-Thouless (BKT) behavior and a 2D-quantum phase(QP)-transition. In an intermediate regime, limited by a gate voltage dependent limiting length, we uncover remarkable consistency with a BKT-critical line ending at a metallic quantum critical point, separating a weakly localized insulator from the superconducting phase. Our estimates for the critical exponents of the 2D-QP-transition, z=1 and nu=0.66, suggest that it belongs to the 3D-xy universality class.Comment: 10 pages, 10 figure