DELTA-IOTA=4 STRUCTURE IN SUPERDEFORMED ROTATIONAL BAND - DEFORMATION WITH C-4V SYMMETRY

The recent observation of ''Delta I = 4 structure'' (or, alternatively, we call it ''Delta I = 2 staggering'') in the rotational spectra of superdeformed nuclei suggests the occurrence of Y-44 deformations in the nuclear shape with associated C-4v point-symmetry for the rotational Hamiltonian. Requiring the axially symmetric terms to favour rotation about an axis that is perpendicular to the long axis of nuclear shape, we have studied the general class of Hamiltonians with such symmetry. The Delta I = 4 structure can indeed result from the tunnelling between the four equivalent minima that occur in the plane perpendicular to the superdeformation symmetry axis, but the occurrence of this effect is a subtle matter depending sensitively on the axially symmetric terms in the Hamiltonian. We also discuss the dependence of the phase and the amplitude of the Delta I = 2 staggering on parameters.