The triaxial nature of low-lying rotational bands of ${}^{166}\mathrm{Er}$ is presented from the viewpoint of the Bohr Hamiltonian and from that of many-fermion calculations by the Monte Carlo shell model and the constrained Hartree-Fock method with projections. A recently proposed novel picture of those bands suggests definite triaxial shapes of those bands, in contrast to the traditional view with the prolate ground-state band and the $\gamma$-vibrational excited band. Excitation level energies and $E2$ transitions can be described well by the Bohr Hamiltonian and by the many-fermion approaches, where rather rigid triaxiality plays vital roles, although certain fluctuations occur in shell-model wave functions. Based on the potential energy surfaces with the projections, we show how the triaxial rigidity appears and what the softness of the triaxiality implies. The excitation to the so-called double $\gamma$-phonon state is discussed briefly.

中文翻译：

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Er166的三轴刚度及其Bohr模型的实现

地下低层旋转带的三轴性质。 ${}^{166}尔$从玻尔·汉密尔顿主义的观点以及蒙特卡罗壳模型和带投影的约束Hartree-Fock方法的多次费米子计算的观点出发，提出了这种方法。最近提出的有关这些带的新颖图片表明，这些带具有确定的三轴形状，这与传统的带有扁平基态带和$\gamma$-振动激发带。激发能级和$Ë2$玻尔哈密顿量和多费米子方法可以很好地描述这种转变，尽管壳模型的波函数会发生某些波动，但刚性三轴性起着至关重要的作用。基于带有投影的势能面，我们显示了三轴刚度如何出现以及三轴刚度的柔软性意味着什么。所谓的双重激励$\gamma$简要讨论了声子状态。