Diverse unconventional density wave states in high-<i>T</i>_c cuprates and other unconventional superconductors

We discuss the mechanism of diverse nematic orders in various strongly correlated electron systems, by considering the interference among different fluctuations given by vertex corrections (VCs). We mainly focus on the ferro- and stripe-bond orders in cuprate superconductors and organic superconductor κ-(BEDT-TTF)₂X. The bond order formation is closely related to the pseudogap phenomena in these systems. We also discuss important effects on bond-order fluctuations on the superconductivity and other electronic properties. We also discuss possible time-reversal-symmetry breaking nematic order based on the Hubbard model.