  We report a large-scale density-matrix renormalization group study of the
lightly doped Hubbard model on 4-leg cylinders at hole doping concentration
$\delta=12.5\%$. By keeping a large number of states for long system sizes, we
are able to reveal a delicate interplay between superconductivity and charge
and spin density wave orders tunable via next-nearest neighbor hopping t'. For
finite t', the ground state is consistent with that of a Luther-Emery liquid,
having `half-filled' charge stripes with power-law superconducting and
charge-density-wave correlations of wave-length $\lambda=1/2\delta$, but
short-range spin correlations. This is in direct contrast to the case with
t'=0, where superconducting correlations fall off exponentially while charge-
and spin-density modulations are dominant. Our results indicate that a route to
robust long-range superconductivity involves destabilizing insulating charge
stripes in the doped Hubbard model.
