Bose-Einstein condensation of five $\alpha$ clusters in $^{20}$Ne and supersolidity

Abstract

We show that the five $\alpha$ cluster states recently observed in $^{20}$Ne, slightly above the five $\alpha$ threshold energy, are Bose-Einstein condensates of five $\alpha$ clusters. The states are described well using a superfluid cluster model, where the order parameter is defined. We suggest that the the five $\alpha$ states are fragmented. Theory predicts the emergence of a five $\alpha$ rotational roton band characterized by a large moment of inertia. This band is formed through roton excitations of the five $\alpha$ BEC vacuum and possesses dual properties of superfluidity and crystallinity, a property of supersolidity. The persistent existence of such a roton bandis discussed and confirmed for the four $\alpha$ condensate above the four $\alpha$ threshold in $^{16}$O and the three $\alpha$ condensate above the three $\alpha$ threshold in $^{12}$C.