Shape coexistence and electric monopole transitions in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Pt}$

Levels in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Pt}$ were studied from the decay of mass-separated ${}_{}{}^{184}{}_{}{}^{}\mathrm{Au}$ by gamma-ray and conversion-electron spectroscopy and by gamma-ray angular distributions from low-temperature nuclear orientation. In addition to coexisting ${\mathit{K}}^{\mathrm{\pi }}$=$0^{+}$ bands, coexisting ${\mathit{K}}^{\mathrm{\pi }}$=$2^{+}$ bands are observed at low energy. String interband electric monopole transitions are observed between states of the two ${\mathit{K}}^{\mathrm{\pi }}$=$0^{+}$ bands and also between states of the two ${\mathit{K}}^{\mathrm{\pi }}$=$2^{+}$ bands. The coexistence of ${\mathit{K}}^{\mathrm{\pi }}$=$2^{+}$ bands at low energy represents a new type of collective structure.