Spin-polarized two dimensional electron gas at the (001) EuTiO3 surface

Di Capua R, Radovic M., Plumb N., Dil J.H., Ristic Z., De Luca G.M., Naamneh M., Verma M., Weber A., Pentcheva R., Salluzzo M.

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II - Fisica della materia
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By using in situ synchrotron radiation high-resolution Angle-Resolved photoemission Spectroscopy (ARPES) and ab initio calculations, we demonstrate the formation of a spin-polarized quasi-two--dimensional electron gas (q2DEG) at the surface of $EuTiO_3$ epitaxial films. While sharing some similarities with the $SrTiO_3$ q2DEG, the $EuTiO_3$ surface state shows distinctive features. Besides the presence of a localized $Eu_{4f}$ band about 2 eV below the Fermi level, the $EuTiO_3$ q2DEG is characterized by heavy bands extending deeper in energy below EF, with a more pronounced hybridization with light bands, compared to the $SrTiO_3$ q2DEG. Ab initio calculations on $TiO_2$ terminated ETO and STO surfaces, including one vertically clustered oxygen di-vacancy in a $2\times 2\times 7$ slab, satisfactorily reproduce the main features of the electronic bands as well as the main differences among the two systems. Furthermore, theoretical calculations show that the $Ti_{3d}$ bands are spin-polarized and in the $EuTiO_3$ q2DEG the exchange coupling between $Ti_{3d}$ and $Eu_{4f}$ states plays a crucial role in stabilizing a ferromagnetic ground state in this system.

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