Nonmonotonic d_(x²-y²)-Wave Superconductivity in Electron-Doped Cuprates Viewing from the Strong-Coupling Side

Applying a variational Monte Carlo method to a two-dimensional t-J model, we study the nonmonotonic d_{x^2-y^2}-wave superconductivity, observed by Raman scattering and ARPES experiments in the electron-doped cuprates. As a gap function in the trial state, we extend the d-wave form (ext.d) so as to have its maxima located near the hot spots of the system. It is found that, in contrast to the hole-doped case, the ext.d wave is always more stable than the simple d wave in the electron-doped case, and the magnetic correlation of the wave vector (\pi,\pi) as well as the pair correlation is enhanced. These results corroborate spin-correlation-mediated superconductivity in cuprates, recently argued from a FLEX calculation. In addition, we confirm that s- and p-wave symmetries are never stabilized even in the over-doped regime.