  Recent experiments revealed a striking asymmetry in the phase diagram of the
high temperature cuprate superconductors. The correlation effect seems strong
in the hole-doped systems and weak in the electron-doped systems. On the other
hand, a recent theoretical study shows that the interaction strengths (the
Hubbard U) are comparable in these systems. Therefore, it is difficult to
explain this asymmetry by their interaction strengths. Given this background,
we analyze the one-particle spectrum of a single band model of a cuprate
superconductor near the Fermi level using the dynamical mean field theory. We
find the difference in the "visibility" of the strong correlation effect
between the hole- and electron-doped systems. This can explain the
electron-hole asymmetry of the correlation strength without introducing the
difference in the interaction strength.
