Claudia Cancellieri

Tunable Rashba spin-orbit interaction at oxide interfaces.

The quasi-two-dimensional electron gas found at the LaAlO{3}/SrTiO{3} 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.

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 cm2/V s. We observe Shubnikov-de Haas oscillations whose period depends only on the perpendicular component of the magnetic field. This observation directly indicates the formation of a two-dimensional electron gas originating from quantum confinement at the interface. From the temperature dependence of the oscillation amplitude we extract an effective carrier mass m* ≃ 1.45 m(e). An electric field applied in the back-gate geometry increases the mobility, the carrier density, and the oscillation frequency.

Influence of the growth conditions on the LaAIO3/SrTiO3 interface electronic properties

The effects of oxygen pressure during the growth of LaAlO3 on (001) SrTiO3, and of post-deposition annealing were investigated. While little influence on the structure was observed, the transport properties were found to depend on both growth pressure and annealing. For LaAlO3 layer thicknesses between 5 and 10 unit cells and growth pressures between 10− 4 and 10−2 mbar, the LaAlO3/SrTiO3 interfaces displayed similar metallic behavior with a sharp transition to a superconducting state. At an oxygen pressure of 10− 6 mbar oxygen vacancies were clearly introduced and extended deep into the SrTiO3 crystal. These vacancies could be removed by post-deposition annealing in 0.2 bar of O2 at ~530 °C. At a growth pressure of 10− 4 mbar, the electronic properties of samples with ultra-thin LaAlO3 layers (2 to 3 unit cells thick) were found to depend markedly on the post-annealing step.

Tunable conductivity threshold at polar oxide interfaces

The physical mechanisms responsible for the formation of a two-dimensional electron gas at the interface between insulating SrTiO(3) and LaAlO(3) have remained a contentious subject since its discovery in 2004. Opinion is divided between an intrinsic mechanism involving the build-up of an internal electric potential due to the polar discontinuity at the interface between SrTiO(3) and LaAlO(3), and extrinsic mechanisms attributed to structural imperfections. Here we show that interface conductivity is also exhibited when the LaAlO(3) layer is diluted with SrTiO(3), and that the threshold thickness required to show conductivity scales inversely with the fraction of LaAlO(3) in this solid solution, and thereby also with the layers formal polarization. These results can be best described in terms of the intrinsic polar-catastrophe model, hence providing the most compelling evidence, to date, in favour of this mechanism.

Doping-dependent band structure of LaAlO3/SrTiO3 interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission

Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO

Growth-induced electron mobility enhancement at the LaAlO3/SrTiO3 interface

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Fabricating superconducting interfaces between artificially grown LaAlO3 and SrTiO3 thin films

/SrTiO

Embedded polytypes in Bi{sub 2}Sr{sub 2-x}La{sub x}CuO{sub 6} thin films grown by laser ablation

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Electrostriction at the LaAlO3/SrTiO3 interface.

in a resonant angle-resolved photoemission experiment. A strong dependence on the light polarization of the Fermi surface and band dispersions is demonstrated, highlighting the distinct Ti 3d orbitals involved in 2D conduction. Samples with different 2D doping levels were prepared and measured by photoemission, revealing different band occupancies and Fermi surface shapes. A direct comparison between the photoemission measurements and advanced first-principle calculations carried out for different 3d-band fillings is presented in conjunction with the 2D carrier concentration obtained from transport measurements.

Interface Fermi States of LaAlO 3 /SrTiO 3 and Related Heterostructures

We have studied the electronic properties of the 2D electron liquid present at the LaAlO3/SrTiO3 interface in series of samples prepared at different growth temperatures. We observe that interfaces fabricated at 650 °C exhibit the highest low temperature mobility ( ≈10 000 cm2 V−1 s−1) and the lowest sheet carrier density ( ≈5×1012 cm−2). These samples show metallic behavior and Shubnikov-de Haas oscillations in their magnetoresistance. Samples grown at higher temperatures (800–900 °C) display carrier densities in the range of ≈2−5×1013 cm−2 and mobilities of ≈1000 cm2 V−1 s−1 at 4 K. Reducing their carrier density by field effect to 8×1012 cm−2 lowers their mobilities to ≈50 cm2 V−1 s−1 bringing the conductance to the weak-localization regime.