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Double dome structure of the Bose–Einstein condensation in diluted S = 3/2 quantum magnets

Yoshito Watanabe, A. Miyake, Gen Masaki, Y. Mizukami, K. Hashimoto, T. Shibauchi, A. Ikeda, M. Tokunaga et al.

Nature Communications, 2023

6 citations

Abstract

Previous studies of magnetic Bose–Einstein condensates have been limited to magnetic materials with small spin numbers. Here the authors study the magnetic phase diagram of a S = 3/2 quantum antiferromagnet and show a double dome structure that is attributed to different types of condensates. Bose–Einstein condensation (BEC) in quantum magnets, where bosonic spin excitations condense into ordered ground states, is a realization of BEC in a thermodynamic limit. Although previous magnetic BEC studies have focused on magnets with small spins of S ≤ 1, larger spin systems potentially possess richer physics because of the multiple excitations on a single site level. Here, we show the evolution of the magnetic phase diagram of S = 3/2 quantum magnet Ba_2CoGe_2O_7 when the averaged interaction J is controlled by a dilution of magnetic sites. By partial substitution of Co with nonmagnetic Zn, the magnetic order dome transforms into a double dome structure, which can be explained by three kinds of magnetic BECs with distinct excitations. Furthermore, we show the importance of the randomness effects induced by the quenched disorder: we discuss the relevance of geometrical percolation and Bose/Mott glass physics near the BEC quantum critical point.

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