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      Anomalous response to gate voltage application in mesoscopic LaAlO_3/SrTiO_3 devices

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          Abstract

          We report on resistivity and Hall measurements performed on a series of narrow mesa devices fabricated from LaAlO_3/SrTiO_3 single interface heterostructure with a bridge width range of 1.5-10 microns. Upon applying back-gate voltage of the order of a few Volts, a strong increase in the sample resistance (up to factor of 35) is observed, suggesting a relatively large capacitance between the Hall-bar and the gate. The high value of this capacitance is due to the device geometry, and can be explained within an electrostatic model using the Thomas Fermi approximation. The Hall coefficient is sometimes a non-monotonic function of the gate voltage. This behavior is inconsistent with a single conduction band model. We show that a theoretical two-band model is consistent with this transport behavior, and indicates a metal to insulator transition in at least one of these bands.

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          A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface.

          Polarity discontinuities at the interfaces between different crystalline materials (heterointerfaces) can lead to nontrivial local atomic and electronic structure, owing to the presence of dangling bonds and incomplete atomic coordinations. These discontinuities often arise in naturally layered oxide structures, such as the superconducting copper oxides and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions. If polarity discontinuities can be atomically controlled, unusual charge states that are inaccessible in bulk materials could be realized. Here we have examined a model interface between two insulating perovskite oxides--LaAlO3 and SrTiO3--in which we control the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface. The hole-doped interface is found to be insulating, whereas the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2 V(-1) s(-1). At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. These results present a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.
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            Electric Field Control of the LaAlO\(_{3}\)/SrTiO\(_{3}\) Interface Ground State

            Interfaces between complex oxides are emerging as one of the most interesting playgrounds in condensed matter physics. In this special setting, in which translational symmetry is artificially broken, a variety of novel electronic phases can be promoted. Theoretical studies predict complex phase diagrams and suggest the key role of the carrier density in determining the systems ground states. A particularly fascinating system is the interface between the insulators LaAlO\(_{3}\) and SrTiO\(_{3}\), which displays conductivity with high mobility. Recently two possible ground states have been experimentally identified: a magnetic state and a two dimensional (2D) superconducting condensate. In this Letter we use the electric field effect to explore the phase diagram of the system. The electrostatic tuning of the carrier density allows an on/off switching of superconductivity and drives a quantum phase transition (QPT) between a 2D superconducting state and an insulating state (2D-QSI). Analyses of the magnetotransport properties in the insulating state are consistent with weak localisation and do not provide evidence for magnetism. The electric field control of superconductivity demonstrated here opens the way to the development of novel mesoscopic superconducting circuits
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              Electric field effect in correlated oxide systems.

              Semiconducting field-effect transistors are the workhorses of the modern electronics era. Recently, application of the field-effect approach to compounds other than semiconductors has created opportunities to electrostatically modulate types of correlated electron behaviour--including high-temperature superconductivity and colossal magnetoresistance--and potentially tune the phase transitions in such systems. Here we provide an overview of the achievements in this field and discuss the opportunities brought by the field-effect approach.
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                Author and article information

                Journal
                06 January 2013
                Article
                10.1103/PhysRevB.87.125409
                1301.1055

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                Custom metadata
                5 pages, 4 figures
                cond-mat.mes-hall

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