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Accueil > Groupes de recherche > Physique des solides > Strongly correlated systems and new electronic states of matter > Novel 2D electron gases at the surface of transition-metal oxides

Novel 2D electron gases at the surface of transition-metal oxides

In solids, the breaking of symmetry at surfaces or interfaces can lead to a reconstruction of the electronic structure and the emergence of novel phenomena of fundamental and applied importance. Paradigmatic examples are the quantum Hall effect, the spin-polarized Dirac-cone states in topological insulators, or the two-dimensional electron gases at semiconductor interfaces, which are at the basis of modern electronics.

Recently, we discovered that metallic two-dimensional electron states can be created at the surface of transparent insulating transition-metal oxides (Fig. 1 and Refs. [1-2]). This is appealing, as these materials are often strongly-correlated electron systems presenting remarkable behavior, such as high temperature superconductivity, colossal magnetoresistance, or photocatalytic capacity. Thus, several of these oxides could also develop, at their surfaces, 2D electron gases with exotic properties, opening fascinating perspectives for fundamental studies of correlated electron systems and for oxide-based electronics, or “OXITRONICS”, one of the most active areas of research in today’s Condensed-Matter Physics.

At present, we are investigating the creation and control of 2D electron states at the surface of different correlated-electron oxides. As part of this activity, we are assembling a lab-based high-resolution ARPES systems coupled to a chamber for thin-film growth. This setup will be used to directly fabricate the 2D electron states, tailor their microscopic properties, and study their electronic structure.

This work benefits from strong experimental and theoretical collaborations with other laboratories at Université Paris-Sud: Laboratoire de Physique de Solides, Thales-Lab, and Institut d’Electronique Fondamentale.

[1] A. F. Santander-Syro, O. Copie, T. Kondo et al. Two-dimensional electron gas with universal subbands at the surface of SrTiO3. Nature 469, 189-193 (2011).

[2] A. F. Santander-Syro, C. Bareille, F. Fortuna et al. Orbital symmetry reconstruction and strong mass renormalization in the two-dimensional electron gas at the surface of KTaO3. Phys. Rev. B 86, 121107(R) (2012).

2D electron gas at the surface of SrTiO3.

Left: Photograph of a transparent insulating sample of SrTiO3 (Paris Metro map on the background).
Right: Density of electrons (color scale) for the sample at the left, displayed as a function of the electron binding energy and momentum (E, k). These data show free-electron-like parabolae (E k^2) quantized in two energy levels by the 2D confinement. As the bands are occupied up to the Fermi level (E_F), the two-dimensional electron gas is metallic. From Ref. [1].