  Unravelling competing orders emergent in doped Mott insulators and their
interplay with unconventional superconductivity is one of the major challenges
in condensed matter physics. To explore possible superconductivity state in the
doped Mott insulator, we study a square-lattice $t$-$J$ model with both the
nearest and next-nearest-neighbor electron hoppings and spin Heisenberg
interactions. By using the state-of-the-art density matrix renormalization
group simulations with imposing charge $U(1)$ and spin $SU(2)$ symmetries on
the large-scale six-leg cylinders, we establish a quantum phase diagram
including three phases: a stripe charge density wave phase, a superconducting
phase without static charge order, and a superconducting phase coexistent with
a weak charge stripe order. Crucially, we demonstrate that the superconducting
phase has a power-law pairing correlation decaying much slower than the charge
density and spin correlations, which is a quasi-1D descendant of the uniform
d-wave superconductor in two dimensions. These findings reveal that enhanced
charge and spin fluctuations with optimal doping is able to produce robust
d-wave superconductivity in doped Mott insulators, providing a foundation for
connecting theories of superconductivity to models of strongly correlated
systems.
