  Photoabsorption cross sections of Nd and Sm isotopes from spherical to
deformed even nuclei are systematically investigated by means of the
quasiparticle-random-phase approximation based on the Hartree-Fock-Bogoliubov
ground states (HFB+QRPA) using the Skyrme energy density functional. The
gradual onset of deformation in the ground states as increasing the neutron
number leads to characteristic features of the shape phase transition. The
calculation well reproduce the isotopic dependence of broadening and emergence
of a double-peak structure in the cross sections without any adjustable
parameter. We also find that the deformation plays a significant role for
low-energy dipole strengths. The $E1$ strengths are fragmented and considerably
lowered in energy. The summed $E1$ strength up to 10 MeV is enhanced by a
factor of five or more.
