Momentum and temperature dependence of renormalization effects in the high-temperature superconductor YBa₂Cu₃O_7−δ

We present a detailed angle-resolved photoemission (ARPES) study of the low-energy electronic structure of YBa₂Cu₃O_7−δ and show that the ARPES spectrum generally contains contribution from two components, of which the prevailing one is hugely overdoped, while the other retains superconductivity and represents the bulk properties. The doping level of the overdoped surface component turns out to be weakly dependent on the oxygen stoichiometry, always remaining close to x∼0.3. By suppressing the overdoped component, we clearly show that the other one develops a superconducting gap consistent with a d-wave symmetry. As in Bi₂Sr₂CaCu₂O_8+δ, the superconducting component is marked by the unusual renormalization which is strongly enhanced at antinodes and vanishes above T_C, supporting the universality of the conclusion regarding the magnetic origin of the unusual renormalization in high-T_C superconductors.