Doping- and Momentum-Dependent Superconducting Gap of Bilayer Cuprate Bi_2Sr_2CaCu_2O_(8+δ) Revealed Using Low-energy ARPES

摘要

We report a systematic study of angle-resolved photoemission spectroscopy on Bi_2Sr_2CaCu_2O_(8+δ) by using low-energy synchrotron radiation. Our focus is on delineating the doping- and momentum-dependent superconducting gap of the bilayer split bands, which are associated with the intracell hybridization of electrons between the two CuO_2 planes. From highly detailed information of gap profile along Fermi surfaces of bonding and antibonding bands, we revealed that a transition temperature T_c is proportional to a nodal-gap energy Δ_N. This result is quantitatively consistent with our findings that the nodal-gap component 2Δ_N is relevant to the antinodal-gap energy Δ~* through a reduction factor of square-root superfluid density ρ_s, as formulated by 8.5k_□ T_c = 2□_□ ∝ □~*{the square root of}□_s. This empirical formula makes an essential contribution to the mechanisms for the unconventional superconductivity.