  In order to investigate the low-energy antiferromagnetic Cu-spin correlation
and its relation to the superconductivity, we have performed muon spin
relaxation (muSR) measurements using single crystals of the electron-doped
high-Tc cuprate Pr_1-x_LaCe_x_CuO_4_ in the overdoped regime. The muSR spectra
have revealed that the Cu-spin correlation is developed in the overdoped
samples where the superconductivity appears. The development of the Cu-spin
correlation weakens with increasing x and is negligibly small in the heavily
overdoped sample where the superconductivity almost disappears. Considering
that the Cu-spin correlation also exist in the superconducting electron-doped
cuprates in the undoped and underdoped regimes [T. Adachi et al., J. Phys. Soc.
Jpn. 85, 114716 (2016)], our findings suggest that the mechanism of the
superconductivity is related to the low-energy Cu-spin correlation in the
entire doping regime of the electron-doped cuprates.
