Magnetic interaction in hole-doped high- T_c superconductors observed by angle-resolved photoemission spectroscopy

We have performed a high-resolution angle-resolved photoemission spectroscopy (ARPES) on high-T_c superconductors (HTSCs) Bi ₂Sr₂Ca_n-1Cu_nO_2n+4 (n=1-3) to study the systematics of the electronic structure and the origin of many-body interactions responsible for superconductivity. We find that a large hole-like Fermi surface and d-wave superconducting gap are generic features of Bi-based HTSCs. For n=2 and 3, a sudden change in the energy dispersion, so-called "kink", becomes pronounced on approaching (π,0) in the superconducting state, while a kink appears only around the nodal direction in the normal state. The kink around (π,0) disappears at T_c. For n=1, the kink shows no significant temperature dependence even across T_c. This could suggest that the coupling of electrons with Q=(π,π) magnetic mode is dominant in the superconducting state for multi-layered cuprates, while the interaction at the normal state and that of single-layered cuprates have a different origin.