ARPES study on many-body interactions in high-T_c cuprates: Origin of kink in energy dispersion

We report a systematic high-resolution ARPES study on Bi₂Sr ₂Ca_n-1Cu_nO_2n+4 (n=1-3). We found two different 'kinks' in the energy dispersion near E_F located at around (π/2, π/2) and (π, 0), respectively. The latter shows a strong temperature and momentum dependence in accordance with the superconductivity while the former shows a less temperature dependence and survives even above T_c. Impurity doping of about 1% drastically weakens the kink near (π, 0) while the kink around (π/2, π/2) is not influenced. The present experimental results indicate that the kink around (π, 0) originates in the coupling of electrons with Q=(π, π) magnetic mode and plays an essential role in the superconductivity while that around (π/2, π/2) has a different origin.