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 $\mu$=0 and 1 branches as the isovector giant dipole resonance where for prolate nuclei the $\mu=0$ mode is lower in energy ($\mu$ being the projection of the axial momentum of the mode). Instead, the toroidal mode exhibits an anomalous (opposite) sequence where the $\mu$=1 branch precedes the $\mu$=0 one.