Triaxiality and shape dynamics in ⁷⁰Ge

The electromagnetic properties of low-lying states in ⁷⁰Ge were investigated via multistep Coulomb excitation of a ⁷⁰Ge beam impinging on a ²⁰⁸Pb target at the ATLAS facility of the Argonne National Laboratory. A total of 27 transitional elements and six diagonal matrix elements coupling 11 low-lying states were extracted from the measured cross sections. These were used to calculate reduced transition probabilities, spectroscopic quadrupole moments, and rotational invariant shape parameters, providing enhanced precision and expanding on previous studies. The experimental data were compared within several theoretical frameworks, including the generalized triaxial rotor model, configuration-interaction shell-model calculations, and computations within the combined frameworks of relativistic density functional theory and the five-dimensional collective Hamiltonian. The results demonstrate a good agreement with the experimental data and, in conjunction with calculations using a two-state mixing model, support significant triaxiality and strong mixing between the 0⁺₁and 0⁺₂ states. This results in the magnitudes of their respective quadrupole deformations [βrms(⁺₁ ) = 0.228 (3), βrms(0⁺₂ ) = 0.273 (1)] being more similar than previously observed. The implications of these results for understanding the complex shape coexistence phenomena, the role of triaxiality, and shape evolution along the Ge isotopic chain are discussed.