Effects of phonon-phonon coupling on properties of pygmy resonance in   $^{124-132}$Sn
  Starting from an effective Skyrme interaction we study effects of phonon-phonon coupling on the low-energy electric dipole response in $^{124-132}$Sn. The QRPA calculations are performed within a finite rank separable approximation. The inclusion of two-phonon configurations gives a considerable contribution to low-lying strength. Comparison with available experimental data shows a reasonable agreement for the low-energy $E1$ strength distribution. 
N.N. Arsenyev, A.P. Severyukhin, V.V. Voronov, Nguyen Van Giai
nucl-th