Pygmy dipole resonances in the calcium isotopes

We present microscopic density functional theory calculations of the total dipole absorption cross sections of the even-A calcium isotopes from ⁴⁰Ca through ⁴⁸Ca. The results reveal the onset of a collective dipole oscillation occurring at low energy and decoupled from the giant dipole resonance. The radial density fluctuations associated with this low-lying mode have the character of the pygmy dipole resonance predicted to exist in neutron rich nuclei.