We have performed high resolution angle-resolved photoemission (ARPES) studies on electron-doped cuprate superconductors ${\mathrm{Sm}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ ($x=0.10$, 0.15, 0.18), ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ ($x=0.15$), and ${\mathrm{Eu}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ ($x=0.15$). Imaginary parts of the electron removal self energy show steplike features due to an electron-bosonic mode coupling. The steplike feature is seen along both nodal and antinodal directions but at energies of 50 and 70 meV, respectively, independent of the doping and rare earth element. Such energy scales can be understood as being due to preferential coupling to half- and full-breathing mode phonons, revealing the phononic origin of the kink structures. Estimated electron-phonon coupling constant $\lambda$ from the self energy is roughly independent of the doping and momentum. The isotropic nature of $\lambda$ is discussed in comparison with the hole-doped case where a strong anisotropy exists.

• Received 6 May 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.117006