Deformation effects in toroidal and compression dipole excitations of 170Yb: Skyrme RPA analysis

The effect of nuclear deformation on the isoscalar toroidal and compression dipole modes in prolate 170 Yb ?> is studied in the framework of the random-phase-approximation method with a representative set of Skyrme forces (SV-bas, SLy6, SkM * ?> and SkI3). It is shown that the deformation crucially redistributes the strength of both modes. The compression mode has the same sequence of &mgr; = 0 ?> and 1 branches as the isovector giant dipole resonance where for prolate nuclei the &mgr; = 0 ?> mode is lower in energy (μ being the projection of the axial momentum of the mode). Instead, the toroidal mode exhibits an unexpected (opposite) sequence where the &mgr; = 1 ?> branch precedes the &mgr; = 0 ?> one.