Island of rare earth nuclei with tetrahedral and octahedral symmetries: Possible experimental evidence

Calculations using realistic mean-field methods suggest the existence of nuclear shapes with tetrahedral T(d) and/or octahedral O(h) symmetries sometimes at only a few hundreds of keV above the ground states in some rare earth nuclei around (156)Gd and (160)Yb. The underlying single-particle spectra manifest exotic fourfold rather than Kramers's twofold degeneracies. The associated shell gaps are very strong, leading to a new form of shape coexistence in many rare earth nuclei. We present possible experimental evidence of the new symmetries based on the published experimental results-although an unambiguous confirmation will require dedicated experiments.