Shape coexistence and the role of axial asymmetry in $^{72}$Ge

The quadrupole collectivity of low-lying states and the anomalous behavior of the 0(2)(+) and 2(3)(+) levels in Ge-72 are investigated via projectile multi-step Coulomb excitation with GRETINA and CHICO-2. Atotal of forty six E2 and M1 matrix elements connecting fourteen low-lying levels were determined using the least-squares search code, GOSIA. Evidence for triaxiality and shape coexistence, based on the model-independent shape invariants deduced from the Kumar-Cline sum rule, is presented. These are interpreted using a simple two-state mixing model as well as multi-state mixing calculations carried out within the framework of the triaxial rotor model. The results represent a significant milestone towards the understanding of the unusual structure of this nucleus. (C) 2016 The Authors. Published by Elsevier B.V.