  The discovery of the charge-density-wave formation in the high-$T_c$ cuprate
superconductors has activated intensive theoretical studies for the pseudogap
states. However, the microscopic origin of the charge-density-wave state has
been unknown so far since the many-body effects beyond the mean-field-level
approximations, called the vertex corrections, are essential. Toward solving
this problem, we employ the recently developed functional renormalization-group
method, by which we can calculate the higher-order vertex corrections in a
systematic and unbiased way with high numerical accuracy. We discover the
critical development of the $p$-orbital-density-wave ($p$-ODW) instability in
the strong-spin-fluctuation region. The obtained $p$-ODW state possesses the
key characteristics of the charge ordering pattern in Bi- and Y-based
superconductors, such as the wave vector parallel to the nearest Cu-Cu
direction, and the $d$-symmetry form factor with the antiphase correlation
between $p_x$ and $p_y$ orbitals in the same unit cell. In addition, from the
observation of the beautiful scaling relation between the spin susceptibility
and the $p$-ODW susceptibility, we conclude that the main driving force of the
density wave is the Aslamazov-Larkin vertex correction that becomes very
singular near the magnetic quantum-critical point.
