Collective magnetic excitations and backbending in fast rotating nuclei

We study in cranked Nilsson plus random phase approximation the electric monopole sE0d, quadrupole sE2d, and magnetic dipole sM1d responses in fast rotating nuclei undergoing backbending, more specifically 156Dy and 158Er. Special attention is paid at the orbital M1 excitations known as scissors mode. We find that the overall strength of the orbital M1 transitions gets enhanced by more than a factor of 4 above the critical backbending region. We show that such a strength evolves with the rotational frequency in close correspondence with the nuclear moment of inertia. This link provides the main clue for understanding the physical origin of such an enhancement, which, if experimentally confirmed, would represent a distinctive feature of nuclei exhibiting backbending.