We provide insights into the backbending phenomenon within the symmetry-adapted framework which naturally describes the intrinsic deformation of atomic nuclei. For ${}^{20}\mathrm{Ne}$, the canonical example of backbending in light nuclei, the ab initio symmetry-adapted no-core shell model shows that while the energy spectrum replicates the backbending from experimental energies under the rotor-model assumption, there is no change in the intrinsic deformation or intrinsic spin of the yrast band around the backbend. For the traditional example of ${}^{48}\mathrm{Cr}$, computed in the valence shell with empirical interactions, we confirm a high-spin nucleus that is effectively near-spherical, in agreement with previous models. However, we find that this spherical distribution results, on average, from an almost equal mixing of deformed prolate shapes with deformed oblate shapes. Microscopic calculations confirm the importance of spin alignment and configuration mixing, but surprisingly unveil no anomalous increase in moment of inertia. This finding opens the path toward further understanding the rotational behavior and moment of inertia of medium-mass nuclei.

• Received 17 May 2022
• Revised 6 June 2023
• Accepted 20 June 2023

DOI:https://doi.org/10.1103/PhysRevC.108.024304