Persistent currents, deformation and collectivity in the many-boson yrast problem on the circle

Properties of the yrast states of a system of $N$ bosons confined to a one-dimensional ring and interacting via contact forces is examined both variationally and by numerical diagonalizations. The latter allow for obtaining numerical correlated many-body wave functions explicitly. The study of correlation functions involving different yrast states indicates that a quantum phase transition previously detected in the properties of the ground state in the case of attractive two-body interactions is an yrast phenomenon involving the onset of `deformation', in the sense given to this term by Bohr and Mottelson in connection with the description of nuclear spectra, including enhanced transition operators and emergence of a shared intrinsic correlation structure. In this case the moment of inertia of the deformed state is essentially the rigid moment of inertia, `intrinsic' states being essentially degenerate.