Orbital symmetry reconstruction and strong mass renormalization in the two-dimensional electron gas at the surface of KTaO3

We study, using angle-resolved photoemission spectroscopy, the two-dimensional electron gas (2DEG) at the surface of KTaO3 (KTO), a wide-gap insulator with strong spin-orbit coupling (SOC). We find that this 2DEG is a genuinely different physical state with respect to the bulk: the orbital symmetries of its subbands are entirely reconstructed and their masses are renormalized. This occurs because the values of the SOC, the Fermi energy, and the subband splittings become comparable in the 2DEG. Additionally, we identify an F-center-like heavy band resulting from the polar nature of the KTO surface.