ΔI=2 Bifurcation as a Characteristic Feature of Scissors Rotational Bands

We report microscopic many-body calculations indicating that rotational bands based on nuclear scissors vibrations exhibit systematic splitting between neighboring spin states ($\mathrm{\ensuremath{\Delta}}I=2$ bifurcation) in which the magnitude of the moment of inertia oscillates between states having even and odd spins. We show that this unexpected result is caused by self-organization of the deformed proton and neutron bodies in the scissors motion, which is further amplified by the ${K}^{\ensuremath{\pi}}={1}^{+}$ two-quasiparticle configurations near the scissors states. We propose that the puzzling excited state found above the ${1}^{+}$ scissors state in $^{156}\mathrm{Gd}$ [Phys. Rev. Lett. 118, 212502 (2017)] is the first evidence of this effect, and predict that bifurcation may generally appear in all other scissors rotational bands of deformed nuclei, and possibly in other systems exhibiting collective scissors vibrations.