Universal Magnetocaloric Effect near Quantum Critical Point of Magnon Bose-Einstein Condensation

Junsen Xiang; Enze Lv; Qinxin Shen; Cheng Su; Xuetong He; Yinghao Zhu; Yuan Gao; Xin-Yang Liu; Dai-Wei Qu; Xinlei Wang; Xi Chen; Qian Zhao; Haifeng Li; Shuo Li; Jie Yang; Jun Luo; Peijie Sun; Wentao Jin; Yang Qi; Rui Zhou; Wei Li; Gang Su

arXiv · 2508.05750

Universal Magnetocaloric Effect near Quantum Critical Point of Magnon Bose-Einstein Condensation

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Abstract

Bose-Einstein condensation (BEC), a macroscopic quantum phenomenon arising from phase coherence and bosonic statistics, has been realized in quantum magnets. Here, we report the observation of a universal magnetocaloric effect (MCE) near a BEC quantum critical point (QCP) in copper sulfate crystal ($CuSO_4 \cdot 5H_2O$). By conducting magnetocaloric and nuclear magnetic resonance measurements, we uncover a field-driven BEC QCP, evidenced by the universal scaling law $T_c \propto (B_c - B)^{2/3}$ and the perfect data collapse of the magnetic Gr\"uneisen ratio. Thermal excitation triggers a dimensional crossover to a 1D quantum-critical regime, where the MCE scaling strictly matches the universality class of 1D Fermi gases. Notably, the quantum-critical MCE enables cooling down to 12.8 mK without helium-3, with very fast thermal relaxation rate that is critical for high cooling power. This work demonstrates the universal MCE in magnon BEC systems, using a common copper sulfate compound as a paradigmatic example, and paves the way for next-generation sub-Kelvin cooling.

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Junsen Xiang, Enze Lv, Qinxin Shen, Cheng Su, Xuetong He, Yinghao Zhu, Yuan Gao, Xin-Yang Liu, Dai-Wei Qu, Xinlei Wang, Xi Chen, Qian Zhao, Haifeng Li, Shuo Li, Jie Yang, Jun Luo, Peijie Sun, Wentao Jin, Yang Qi, Rui Zhou, Wei Li, Gang Su. 2025-08-07. Universal Magnetocaloric Effect near Quantum Critical Point of Magnon Bose-Einstein Condensation. https://arxiv.org/abs/2508.05750

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