Electronic Orbital Reconstruction at (110)-oriented LaAlO$_{3}$/SrTiO$_{3}$ interfaces

About ten years ago, a two-dimensional gas (2DEG) was discovered at the interface between two insulators: SrTiO$_{3}$ (STO) and LaAlO$_{3}$ (LAO). Later on, superconductivity as well magnetism were reported, making the LAO/STO interface an extremely intriguing system. So far the research was essentially directed to the (001)-interface, along which a built-in electrostatic potential is thought to generate the 2DEGs. Recently, however, high-mobility 2DEGs have been discovered along other directions, including \textless 110\textgreater for which such a built-in potential was unexpected. Yet, a direct fingerprint of the distinctive nature of the electronic structure at the (110)- interface has not been provided. Here, based on X-ray linear dichroism (XLD) experiments we show explicitly the dissimilar hierarchy of the electronic states at the (001)- and (110)- interfaces. In particular, our XLD experiments demonstrate that the degeneracy is fully removed in the t$_{\mathrm{2g}}$ and the e$_{\mathrm{g}}$ levels. Contrary to (001)- interfaces --where the first accessible orbitals are dxy--, our DFT calculations show, in agreement with XLD, a very strong contribution of the dxz/dyz orbitals at the first available levels in energy at (110)-interfaces.