The LaAlO 3 =SrTiO 3 interface hosts a two-dimensional electron system that is unusually sensitive to the application of an in-plane magnetic field. Low-temperature experiments have revealed a giant negative magnetoresistance (dropping by 70%), attributed to a magnetic-field induced transition between interacting phases of conduction electrons with Kondo-screened magnetic impurities. Here we report on experiments over a broad temperature range, showing the persistence of the magnetoresistance up to the 20 K rangeindicative of a single-particle mechanism. Motivated by a striking correspondence between the temperature and carrier density dependence of our magnetoresistance measurements we propose an alternative explanation. Working in the framework of semiclassical Boltzmann transport theory we demonstrate that the combination of spin-orbit coupling and scattering from finite-range impurities can explain the observed magnitude of the negative magnetoresistance, as well as the temperature and electron density dependence. The mobile electrons at the LaAlO 3 =SrTiO 3 (LAO=STO) interface [1] display an exotic combination of superconductivity [2,3] and magnetic order [4][5][6][7]. The onset of superconductivity at sub-Kelvin temperatures appears in an interval of electron densities where the effect of Rashba spin-orbit coupling on the band structure at the Fermi level is strongest [8,9], but whether this correlation implies causation remains unclear.Transport experiments above the superconducting transition temperature have revealed a very large ("giant") drop in the sheet resistance of the LAO=STO interface upon application of a parallel magnetic field [10][11][12][13]. An explanation has been proposed [13,14] in terms of the Kondo effect: Variation of the electron density or magnetic field drives a quantum phase transition between a highresistance correlated electronic phase with screened magnetic impurities and a low-resistance phase of polarized impurity moments. The relevance of spin-orbit coupling for magnetotransport is widely appreciated [10,[14][15][16][17][18][19], but it was generally believed to be too weak an effect to provide a single-particle explanation of the giant magnetoresistance.In this work we provide experimental data (combining magnetic field, gate voltage, and temperature profiles for the resistance of the LAO=STO interface) and theoretical calculations that support an explanation fully within the single-particle context of Boltzmann transport. The key ingredients are the combination of spin-orbit coupling, band anisotropy, and finite-range electrostatic impurity scattering.The thermal insensitivity of the giant magnetoresistance [10,11], in combination with a striking correspondence that we have observed between the gate voltage and temperature dependence of the effect, are features that are difficult to reconcile with the thermally fragile Kondo interpretationbut fit naturally in the semiclassical Boltzmann description.We first present the experimental data and then turn to the theoretical de...

Cataloged from PDF version of article.We report on the fabrication and characterization of solution-processed, highly flexible, silicon nanowire network based metal-semiconductor-metal photodetectors. Both the active part of the device and the electrodes are made of nanowire networks that provide both flexibility and transparency. Fabricated photodetectors showed a fast dynamic response, 0.43 ms for the rise and 0.58 ms for the fall-time, with a decent on/off ratio of 20. The effect of nanowire-density on transmittance and light on/off behavior were both investigated. Flexible photodetectors, on the other hand, were fabricated on polyethyleneterephthalate substrates and showed similar photodetector characteristics upon bending down to a radius of 1 cm. © 2013 AIP Publishing LLC

Novel physical phenomena arising at the interface of complex oxide heterostructures offer exciting opportunities for the development of future electronic devices. Using the prototypical LaAlO3/SrTiO3 interface as a model system, we employ a single-step lithographic process to realize gate-tunable Josephson junctions through a combination of lateral confinement and local side gating. The action of the side gates is found to be comparable to that of a local back gate, constituting a robust and efficient way to control the properties of the interface at the nanoscale. We demonstrate that the side gates enable reliable tuning of both the normal-state resistance and the critical (Josephson) current of the constrictions. The conductance and Josephson current show mesoscopic fluctuations as a function of the applied side gate voltage, and the analysis of their amplitude enables the extraction of the phase coherence and thermal lengths. Finally, we realize a superconducting quantum interference device in which the critical currents of each of the constriction-type Josephson junctions can be controlled independently via the side gates.

The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (T; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-T superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

We develop a robust and versatile platform to define nanostructures at oxide interfaces via patterned top gates. Using LaAlO3/SrTiO3 as a model system, we demonstrate controllable electrostatic confinement of electrons to nanoscale regions in the conducting interface. The excellent gate response, ultra-low leakage currents, and long term stability of these gates allow us to perform a variety of studies in different device geometries from room temperature down to 50 mK. Using a split-gate device we demonstrate the formation of a narrow conducting channel whose width can be controllably reduced via the application of appropriate gate voltages. We also show that a single narrow gate can be used to induce locally a superconducting to insulating transition. Furthermore, in the superconducting regime we see indications of a gate-voltage controlled Josephson effect.Despite decades of intense study, transition metal oxides continue to reveal fascinating and unexpected physical properties that arise from their highly correlated electrons [1]. Propelled by recent developments in oxides thin film technology it has now become possible to create high quality interfaces between such complex oxides, which reveal a new class of emergent phenomena often non-existent in the constituent materials [2,3]. In particular, there has been a growing interest in interfaces that host a conducting two dimensional electron system (2DES) [4,5]. This 2DES has been shown to support high mobility electrons [5][6][7], magnetism [8] and superconductivity [9]. In addition to this inherently rich phase space, in-situ electrostatic gating can be used not only to alter the carrier density [10], but it can significantly change the spin-orbit coupling (SOC) [11,12] and even drive transitions from a superconducting to an insulating state [13].Bulk transport studies of oxide interfaces have played an important role toward building a better understanding of these new material systems. However, it is becoming increasingly clear that in order to fully grasp the details of the complex coexisting phases at the interface, one must probe the system at much smaller length scales. Recent scanning probe experiments have indeed clearly demonstrated that the electronic properties of the interface can change dramatically over microscopic length scales [14][15][16]. In this context, nanoscale electronic devices could provide direct information on how such strong local variations in physical properties affect mesoscopic charge transport. Perhaps even more exciting is the possibility of discovering and manipulating new electronic states that are predicted to arise from the interplay between confinement, superconductivity and SOC [17]. Furthermore, the ability to locally drive phase transitions at the interface could potentially yield technologically relevant oxide-based nano-electronic devices with novel functionality [18].Existing methods for confinement at the interface involve some form of nanoscale patterning, which renders selected portions of the interface insulati...

One of the hallmark experiments of quantum transport is the observation of the quantized resistance in a point contact in GaAs/AlGaAs heterostructures. Being formed with split gate technology, these structures represent in an ideal manner equilibrium reservoirs which are connected only through a few electron mode channel. It has been a long standing goal to achieve similar experimental conditions also in superconductors. Here we demonstrate the formation of a superconducting quantum point contact (SQPC) with split gate technology in a two-dimensional superconductor, utilizing the unique gate tunability of the superfluid at the LaAlO3/SrTiO3 interface. When the constriction is tuned through the action of metallic split gates we identify three regimes of transport: First, SQPC for which the supercurrent is carried only by a few quantum transport channels. Second, superconducting island strongly coupled to the equilibrium reservoirs. Third, charge island with a discrete spectrum weakly coupled to the reservoirs.

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