Bose–Einstein condensation of five clusters in Ne and supersolidity

S. Ohkubo; J. Takahashi; Y. Yamanaka

doi:10.1140/epjp/s13360-025-06049-x

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2024 Impact factor 2.9

EPJ PLUS - Condensed Matter and Complex Systems

Eur. Phys. J. Plus (2025) 140: 118
https://doi.org/10.1140/epjp/s13360-025-06049-x

Regular Article

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

S. Ohkubo¹^a, J. Takahashi² and Y. Yamanaka³

¹ Research Center for Nuclear Physics, Osaka University, 567-0047, Ibaraki, Japan
² Faculty of Economics, Asia University, 180-0022, Tokyo, Japan
³ Institute of Condensed-Matter Science, Waseda University, 169-8555, Tokyo, Japan

^a ohkubo@rcnp.osaka-u.ac.jp

Received: 6 December 2024
Accepted: 22 January 2025
Published online: 11 February 2025

Abstract

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

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© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2025

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.