  We study competitions between charge uniform and inhomogeneous states in
two-dimensional Hubbard models by using a variational Monte Carlo method. At
realistic parameters for cuprate superconductors, emergent effective attraction
of carriers generated from repulsive Coulomb interaction leads to charge/spin
stripe ground states, which severely compete with uniform superconducting
excited states in the energy scale of 10 K for the cuprates. Stripe period
increases with decreasing hole doping $\delta$, which agrees with the
experiments for La-based cuprates at $\delta$ = 1/8. For lower $\delta$, we
find a phase separation. Implications of the emergent attraction for the
cuprates are discussed.
