  The underlying structure of low-lying collective bands of atomic nuclei is
discussed from a novel perspective on the interplay between single-particle and
collective degrees of freedom, by utilizing state-of-the-art configuration
interaction calculations on heavy nuclei. Besides the multipole components of
the nucleon-nucleon interaction that drive collective modes forming those
bands, the monopole component is shown to control the resistance against such
modes. The calculated structure of 154Sm corresponds to coexistence between
prolate and triaxial shapes, while that of 166Er exhibits a deformed shape with
a strong triaxial instability. Both findings differ from traditional views
based on beta/gamma vibrations. The formation of collective bands is shown to
be facilitated from a self-organization mechanism.
