Systematic Features Indicative of Shape Coexistence in the Doubly-Even N=90 Isotones

The $N=90$ nuclei near stability ($^{150}$Nd, $^{152}$Sm, $^{154}$Gd, and $^{156}$Dy) are at the onset of stable nuclear deformation and have often been labeled as ``soft'' nuclei. Results from recent experimental and theoretical studies of these nuclei challenge this interpretation, however, and indicate instead strong mixing of near-degenerate coexisting quasi-rotational bands with different deformations. Details of these studies and data from recent experiments focused on $^{156}$Dy, $^{158}$Er, and $^{160}$Yb using the $8\pi$ Spectrometer at TRIUMF/ISAC will be presented.