Rotational perturbation to the natural-parity rotational band of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Dy</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>163</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>

Reduced transition probabilities of B(M1) and B(E2) are determined up to spin (23/2 on the basis of a Coulomb excitation experiment. Strong signature-dependent staggering was observed for \ensuremath{\Delta}I=1 M1 transition probabilities. In contrast, there was no significant signature dependence observed for \ensuremath{\Delta}I=1 and \ensuremath{\Delta}I=2 E2 transition probabilities as well as for level energies. We carried out a rotating-shell-model calculation with the \ensuremath{\gamma} degree of freedom. The origin of the unexpected signature dependence of the B(M1) is shown to be due to the characteristic coherence between the orbital and the spin contributions. We also show that the coupling with the \ensuremath{\gamma}-vibrational phonons makes it possible to reproduce the absolute values of the B(M1) at high-spin states without using the phenomenological ${g}_{R}$. Both the stretched and nonstretched B(E2)'s are well reproduced in the rotating shell model without assuming triaxiality.

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