MaNEP e-Newsletter MaNEP Nr. 20
Scientific Highlight
Tuning the LaAlO3/SrTiO3 interface ground state using the electric field effect
By Stefano Gariglio

The electric field effect, at the heart of every electronic device, allows the carrier density to be modulated and is thus a powerful technique to explore the electronic properties of a material. Applying this principle to switch on and off superconductivity has been a dream since the sixties. This has however proven to be a difficult task as field effect devices require an ultrathin low carrier density superconducting material in contact with a robust high permittivity gate dielectric. A particularly interesting system appeared in 2004 when Othomo and Hwang discovered that the interface between two band insulators, LaAlO3 and SrTiO3, is conducting. This immediately calls to mind the two dimensional (2D) electron gas generated in semiconductor heterostructures. Correlated oxide systems are however complex materials much richer than semiconductors as Nicolas Reyren and colleagues, in the group of Jean-Marc Triscone (University of Geneva), proved in 2007 by discovering that this metallic interface undergoes a 2D superconducting transition at around 200 mK [1] [2]. The team soon realized that the configuration of this system, a low carrier density superconducting sheet, 10 nm thick, confined between two dielectrics, offers a unique opportunity for exploring the electric field modulation of superconductivity.

The award ceremony at Innsbruck showing Nicolas Reyren and Stefano Gariglio receiving the award from Christophe Rossel, president of the Swiss Physical Society. Andrea Caviglia was absent.

Electric field devices, realized using the SrTiO3 crystal as a gate dielectric, have disclosed a rich phase diagram, with a quantum critical point separating an insulating ground state from a 2D superconducting state [3]. These experiments illustrate how a quantum phase transition can be driven by the application of an electric field. They also demonstrate for the first time a continuous and reversible modulation of the superconducting state.

In its annual 2009 meeting in Innsbruck, the Swiss Physical Society has recognized the prominence of these results in the award ceremony, attributing the Applied Physics Award, sponsored by OC Oerlikon, to Andrea Caviglia, Stefano Gariglio and Nicolas Reyren.

This discovery, beyond offering the possibility to study quantum phase transitions in low dimensions, opens the way to the fabrication of new mesoscopic devices where the superconducting state can in principle be switched on and off at the nanoscale.

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