Marcin Raczkowski, University of Würzburg
Recent scanning tunneling microscopy on two different cuprate families Ca_{2-x}Na_xCuO_2Cl_2 and Bi_2Sr_2Dy_{0.2}Ca_{0.8}Cu_2O_{8+\delta} has revealed unidirectional bond-centered modulation in local electronic density of states. Motivated by this result we investigate the emergence of spontaneous modulations in the d-wave superconducting resonating valence bond phase using the t-J model at x=1/8 doping. Half-filled charge domains separated by four lattice spacings are found to form along one of the crystal axes leading to modulated superconductivity with either {\it inphase} or {\it antiphase} d-wave order parameters in neighboring domains. Both renormalized mean-field theory and variational Monte Carlo calculations yield that the energy of the modulated solutions (especially of the inphase one) approaches the energy of the uniform d-wave RVB superconductor and the energy difference can be further reduced by the tetragonal lattice distortion that often appears in high-T_c compounds. Moreover, we have also found closely related stripe phase originating from the staggered flux phase, a candidate for the pseudogap normal phase of lightly doped cuprates.