We performed high-field magnetization, magnetocaloric effect (MCE), and NMR measurements on the Ising triangular-lattice antiferromagnet Rb2Co(SeO3)2. The observations of the 1/3-magnetization plateau, the split NMR lines, and the thermal activation behaviors of the spin-lattice relaxation rate 1/T1 between 2 T and 15.8 T provide unambiguous evidence of a gapped up-up-down (UUD) magnetic ordered phase. For fields between 15.8 T and 18.5 T, the anomaly in the magnetic susceptibility, the slow saturation of the NMR line spectral ratio with temperature, and the power-law temperature dependence of 1/T1 suggest the ground state to be a spin supersolid with gapless spin excitations. With further increasing the field, the Gr\"{u}neisen ratio, extracted from the MCE data, reveals a continuous quantum phase transition at HC≈ 19.5 T and a universal quantum critical scaling with the exponents νz≈1. Near HC, the large high-temperature MCE signal and the broad peaks in the NMR Knight shift and 1/T1, manifest the strong spin fluctuations driven by both magnetic frustration and quantum criticality. These results establish Rb2Co(SeO3)2 as a candidate platform for cryogenic magnetocaloric cooling.
@article{arxiv.2509.26151,
title = {Spin-supersolidity induced quantum criticality and magnetocaloric effect in the triangular-lattice antiferromagnet Rb$_2$Co(SeO$_3$)$_2$},
author = {Yi Cui and Zhanlong Wu and Zhongcen Sun and Kefan Du and Jun Luo and Shuo Li and Jie Yang and Jinchen Wang and Rui Zhou and Qian Chen and Yoshimitsu Kohama and Atsuhiko Miyata and Zhuo Yang and Rong Yu and Weiqiang Yu},
journal= {arXiv preprint arXiv:2509.26151},
year = {2026}
}