  The ground state of the t-t'-J ladder with four legs favors a striped charge
distribution for the parameters corresponding to hole-doped cuprate
superconductors. We investigate the dynamical spin and charge structure factors
of the model by using the dynamical density matrix renormalization group (DMRG)
and clarify the influence of the stripe on the structure factors. The dynamical
charge structure factor along the momentum direction from q=(0,0) to (pi,0)
clearly shows low-energy excitations corresponding to the stripe order in hole
doping. On the other hand, the stripe order weakens in electron doping,
resulting in fewer low-energy excitations in the charge channel. In the spin
channel, we find incommensurate spin excitations near q=(pi,pi) forming an
hourglass behavior in hole doping, while in electron doping we find clearly
spin-wave-like dispersions starting from q=(pi,pi). Along the (0,0)-(pi,0)
direction, the spin excitations are strongly influenced by the stripes in hole
doping, resulting in two branches that form a discontinuous behavior in the
dispersion. In contrast, the electron-doped systems show a downward shift in
energy toward (pi,0). These behaviors along the (0,0)-(pi,0) direction are
qualitatively similar to momentum-dependent spin excitations recently observed
by resonant inelastic x-ray scattering experiments in hole- and electron-doped
cuprate superconductors.
