Understanding the different rotational behaviors of 252 No and 254 No

Total Routhian surface calculations have been performed to investigate rapidly rotating transfermium nuclei, the heaviest nuclei accessible by detailed spectroscopy experiments. The observed fast alignment in No and slow alignment in No are well reproduced by the calculations incorporating high-order deformations. The different rotational behaviors of No and No can be understood for the first time in terms of β6 deformation that decreases the energies of the νj15/2 intruder orbitals below the N = 152 gap. Our investigations reveal the importance of high-order deformation in describing not only the multi-quasiparticle states but also the rotational spectra, both providing probes of the single-particle structure concerning the expected doubly-magic superheavy nuclei.