Two-Dimensional Superconductivity at Titanium Oxide Interfaces.

Abstract : We have investigated the electronic transport at the interface of two insulating oxides : SrTiO3 and LaTiO3. A two-dimensional electron gas (2DEG) is formed when a polar interface is created at the surface of an un-doped SrTiO3 substrate. This has been reported for several insulating oxide forming the interface (LaAlO3, LaVO3, LaGaO3,...). In this work we focus on the interface with the Mott insulator LaTiO3. We have shown that the 2DEG at this interface is metallic and superconducting at very low temperature. We have also modulated its transport properties by electric field effect. The Hall effect measured at very high magnetic field has shown that the 2DEG consist of two types of carriers : a majority of carriers have a low mobility, and a minority of carriers have a higher mobility. We have developed a band bending model of the interface which shows that the low mobility carriers are confined near the interface in the lowest sub-bands, whereas the high mobility carriers are controlled by the filling and spatial extension of sub-bands of higher energy. Superconductivity is linked to the appearance of these high mobility carriers. The quantum critical behaviour of the superconductor to insulator transition induced by magnetic field reveals that those high mobility carriers are spread in puddles of mesoscopic sizes. Magnetoresistance measurements evidence the presence of a strong Rashba spin-orbit coupling at the interface, which can also be modulated by electric field effect.
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Johan Biscaras. Two-Dimensional Superconductivity at Titanium Oxide Interfaces.. Supraconductivité [cond-mat.supr-con]. Université Pierre et Marie Curie - Paris VI, 2012. Français. ⟨pastel-00779961⟩

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