Masafumi Horio (UZH)
Whereas single-band theories have long been the dominating paradigm applied to cuprate superconductors, recent theoretical studies have highlighted the implications of orbital hybridization in the cuprates. Hybridization of the dx2-y2 band with the dz2 band increases with reducing apical oxygen height which in turn lowers the superconducting transition temperature. In light of these theoretical predictions, we have performed angle-resolved photoemission spectroscopy (ARPES) studies on the cuprate La2-xSrxCuO4 (x = 0.23). By recording ARPES spectra down to ~ 2 eV below the Fermi level, not the only well-documented dx2-y2 band but also the dz2 band was successfully identified. We clearly observed a hybridization gap between those two bands along the antinodal (p, 0) direction, which is the direct experimental evidence of the orbital hybridization. This is in stark contrast with the nodal (p, p) direction where the opposite mirror symmetry between the dx2-y2 and dz2 band prohibits their hybridization and constitute a two-dimensional type-II Dirac nodal line. Our results thus indicate that the multi-band nature in cuprates involves a wealth of physics: from high-temperature superconductivity to symmetry-protected band structures.
