In-Medium Generator Coordinate Method with Explicit Quasiparticle Excitations

Shape co-existence is a phenomenon in which a nucleus exhibits states with different intrinsic shapes at nearly degenerate energies. The intrinsic density distributions can be spherical, prolate, oblate, or manifest as some complex combination. For the description of such states, we implement the so-called in-medium generator coordinate method (IM-GCM), which incorporates the expansion of nuclear wavefunctions in terms of deformed basis configurations with in-medium similarity renormalization group (IMSRG) techniques to capture both dynamical (i.e. few-body) and static collective correlations of open-shell nuclei in the medium- and heavy-mass region. We extend the (IM-)GCM by including few-quasiparticle excitations to enable the description of odd nuclei and general states that require unpaired degrees of freedom. We will present first results for energies and transitions in selected nuclei.