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Register a new userFrictional drag between superconducting LaAlO$_3$/SrTiO$_3$ nanowires
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We report frictional drag measurements between two superconducting LaAlO$_3$/SrTiO$_3$ nanowires. In these experiments, current passing through one nanowire induces a voltage across a nearby electrically isolated nanowire. The frictional drag signal contains both symmetric and antisymmetric components. The antisymmetric component arises from the rectification of quantum shot noise in the drive nanowire by the broken symmetry in the drag nanowire. The symmetric component in the drag resistance is ascribed to rectification of thermal noise in the drive nanowire during superconducting-normal transition. The suppression of the symmetric component is observed when a normal nanowire is used as either a drag or drive nanowire with the other nanowire superconducting. The absence of symmetric drag resistance between a normal drag nanowire and a superconducting drive nanowire suggests a higher electron-hole asymmetry in the superconducting LaAlO$_3$/SrTiO$_3$ nanowire arising from the 1D nature of superconductivity at LaAlO$_3$/SrTiO$_3$ interface.
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A number of recent studies indicate that the charge conduction of the LaAlO$_3$/SrTiO$_3$ interface at low temperature is confined to filaments which are linked to structural domain walls in the SrTiO$_3$ with drastic consequences for example for the temperature dependence of local transport properties. We demonstrate that as a consequences of this current carrying filaments on the nano-scale the magnetotransport properties of the interface are highly anisotropic. Our magnetoresistance measurements reveal that the magnetoresistance in different nanostructures ($<500nm$) is random in magnitude and sign, respectively. Warming up nanostructures above the structural phase transition temperature (105K) results in the significant change in MR. Even a sign change of the magnetoresistance is possible. The results suggest that domain walls that are differently oriented with respect to the surface exhibit different respective magnetoresistance and the total magnetoresistance is a result of a random domain wall pattern formed during the structural phase transition in the SrTiO$_3$ at cool down.
The transport and thermoelectric properties of the interface between SrTiO$_3$ and a 26-monolayer thick LaAlO$_3$-layer grown at high oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and in magnetic fields up to 18 T. For $T>$ 4.2 K, two different electron-like charge carriers originating from two electron channels which contribute to transport are observed. We probe the contributions of a degenerate and a non-degenerate band to the thermoelectric power and develop a consistent model to describe the temperature dependence of the thermoelectric tensor. Anomalies in the data point to an additional magnetic field dependent scattering.
We describe the transport properties of mesoscopic devices based on the two dimensional electron gas (2DEG) present at the LaAlO$_3$/SrTiO$_3$ interface. Bridges with lateral dimensions down to 500~nm were realized using electron beam lithography. Their detailed characterization shows that processing and confinement do not alter the transport parameters of the 2DEG. The devices exhibit superconducting behavior tunable by electric field effect. In the normal state, we measured universal conductance fluctuations, signature of phase-coherent transport in small structures. The achievement of reliable lateral confinement of the 2DEG opens the way to the realization of quantum electronic devices at the LaAlO$_3$/SrTiO$_3$ interface.
At the LaAlO$_3$-SrTiO$_3$ interface, electronic phase transitions can be triggered by modulation of the charge carrier density, making this system an excellent prospect for the realization of versatile electronic devices. Here, we report repeatable transistor operation in locally gated LaAlO$_3$-SrTiO$_3$ field-effect devices of which the LaAlO$_3$ dielectric is only four unit cells thin, the critical thickness for conduction at this interface. This extremely thin dielectric allows a very efficient charge modulation of ${sim}3.2times10^{13}$ cm$^{-2}$ within a gate-voltage window of $pm1$ V, as extracted from capacitance-voltage measurements. These also reveal a large stray capacitance between gate and source, presenting a complication for nanoscale device operation. Despite the small LaAlO$_3$ thickness, we observe a negligible gate leakage current, which we ascribe to the extension of the conducting states into the SrTiO$_3$ substrate.
Novel physical phenomena arising at the interface of complex oxide heterostructures offer exciting opportunities for the development of future electronic devices. Using the prototypical LaAlO$_3$/SrTiO$_3$ 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.
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