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« Novel 2D electron gases at the surface of transition-metal oxides : role of topology and spin-orbit coupling » - Andres Santander-Syro - Mardi 18 novembre 2014 à 11h

Andres Santander-Syro - Centre de Sciences Nucléaires et de Sciences de la Matière
Mardi 18 novembre 2014 à 11h - INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32- 2e étage, salle 201

Abstract

Transition-metal oxides (TMOs) are correlated-electron systems with remarkable properties, such as high-temperature superconductivity or large magnetoresistance. The realization of two-dimensional electron gases (2DEGs) at surfaces or interfaces of TMOs, a field of current active research, is crucial for harnessing the functionalities of these materials for future applications. Additionally, these 2DEGs offer the possibility to explore new physics emerging from the combined effects of electron correlations and low-dimensional confinement.

Recently, we discovered that a 2DEG is simply realized at the bare surface of SrTiO3, a transparent, insulating TMO with a gap of 3.5 eV.

We directly imaged its multiple heavy and light subbands using angle-resolved photoemission spectroscopy [1]. In this talk, I will show that one can also create and tailor 2DEGs in other TMO surfaces, opening vast possibilities for the study of correlations in low dimensions in materials showing diverse functionalities. I will first discuss the specific case of KTaO3, a wide-gap insulator with a spin-orbit coupling 30 times larger than in SrTiO3. I will show that quasi-2D confinement in this system results in comparable scales for the Fermi energy, the subband splitting, and the spin-orbit coupling, leading to a complete reconstruction of the orbital symmetries and band masses [2]. Then, I will show that by choosing various surface terminations, one can modify the electronic structure and symmetries of the 2DEGs at the surface of TMOs [3, 4]. Finally, I will discuss our recent observation of a giant spin splitting, of 100 meV, of bands with opposite spin chiralities in the 2DEG at the surface of SrTiO3 [5]. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are not simple extensions of the bulk bands, and are promising for technological applications.

1) A. F. Santander-Syro et al., Nature 469, 189 (2011). 2) A. F. Santander-Syro et al., Phys. Rev. B 86, 121107(R) (2012). 3) C. Bareille et al., Sci. Rep. 4, 3586 (2014). 4) T. Rödel et al., Phys. Rev. Applied 1, 051002 (2014). 5) A. F. Santander-Syro et al., Nature Mater. DOI : 10.1038/NMAT4107 (2014).