Differences in the high-energy kink between hole- and electron-doped high-Tc superconductors

We have performed an angle-resolved photoemission spectroscopy (ARPES) study of Nd1.85Ce0.15CuO4 (NCCO) in order to elucidate the origin of the high-energy kink (HEK) observed in the high-T-c superconductors (HTSCs). The energy scale of the HEK in NCCO is large compared with that in hole-doped HTSCs, consistent with previous ARPES studies. From measurement in a wide momentum region, we have demonstrated that between the hole- and electron-doped HTSCs, the energy position of the HEK is shifted approximately by the amount of the chemical potential difference. Also, we have found that around (pi,0) the HEK nearly coincides with the band bottom while around the node the band reaches the incoherent region and the HEK appears at the boundary between the coherent and incoherent regions.