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Discovery of Spin-supersolidity Induced Quantum Criticality in the Triangular-Lattice Antiferromagnet Rb2Co(SeO3)2

A collaborative research team led by Atsuhiko Miyata (Associate Professor) and Zhuo Yang (Project Research Associate) from the Institute for Solid State Physics (ISSP), the University of Tokyo, in partnership with Weiqiang Yu (Professor) and Yi Cui (Associate Professor) from Renmin University of China, has identified a field-induced spin-supersolid phase in the Ising triangular-lattice antiferromagnet Rb2Co(SeO3)2. By employing high-field magnetization, Nuclear Magnetic Resonance (NMR), and magnetocaloric effect (MCE) measurements, the team successfully characterized the exotic quantum critical behavior associated with this unique state.

fig1
Figure 1. Magnetic phase diagram and quantum critical scaling of Rb2Co(SeO3)2. The H-T phase diagram illustrates the boundaries between the UUD, V-type SS, and FP phases determined by magnetization, NMR, and MCE data. The background color represents the adiabatic T(H) curves, showing a minimum at HC ≈ 19.5 T.

Spin supersolidity, a quantum state combining broken translational symmetry and superfluid-like coherence, has long been sought in frustrated quantum magnets. Although theoretical studies have predicted spin-supersolid phases in triangular-lattice antiferromagnets, their experimental identification and their interplay with quantum criticality remain largely unexplored. Here, high-field magnetization, magnetocaloric effect (MCE), and nuclear magnetic resonance (NMR) measurements on the Ising triangular-lattice antiferromagnet Rb2Co(SeO3)2 reveal a field-induced spin-supersolid phase and its associated quantum critical behavior.

Fig. 1 shows the magnetic phase diagram of Rb2Co(SeO3)2 with magnetic fields up to 36 Tesla(T), revealing a sequence of exotic field-induced quantum phases [1]. At low fields between 2 and 15.8 T, a robust 1/3-magnetization plateau together with activated behavior of the NMR spin-lattice relaxation rate 1/T1 provides clear evidence for a gaped UUD phase. Increasing the magnetic field drives the system into a V-type spin-supersolid phase between 15.8 and 18.5 T. In contrast to the UUD state, this phase exhibits gapless spin excitations characterized by a power-law temperature dependence 1/T1∝T5, consistent with theoretical expectations for a spin supersolid in frustrated Ising magnets [1,2]. Above HC≈19.5T, the system undergoes a continuous quantum phase transition into the FP phase.

Pulsed-field MCE measurements performed under adiabatic conditions at ISSP further reveal pronounced quantum critical behavior near HC. The magnetic Grüneisen ratio ΓH exhibits a diverging tendency upon cooling and collapses onto a universal scaling function with critical exponent νz≈1, consistent with (3+2)D mean-field universality [1]. Near the critical field, competing magnetic orders and quantum critical fluctuations generate strong entropy accumulation, producing an unusually large magnetocaloric response. Remarkably, the cooling effect near HCeven exceeds that at zero field, highlighting the potential of spin supersolids as platforms for high-field cryogenic cooling [3].

These results establish Rb2Co(SeO3)2 as a promising platform for exploring the interplay between supersolidity, frustration, and quantum criticality. More broadly, this work demonstrates how competing quantum orders in frustrated magnets can enhance entropy fluctuations and generate emergent thermodynamic responses with potential applications in quantum magnetic cooling.

Publication

  • Journal：npj Quantum Materials
  • Title：Spin-supersolidity Induced Quantum Criticality in the Triangular-Lattice Antiferromagnet Rb2Co(SeO3)2
  • Authors：Yi Cui, Zhanlong Wu, Zhongcen Sun, Kefan Du, Jun Luo, Shuo Li, Jie Yang, Jinchen Wang, Rui Zhou, Qian Chen, Yoshimitsu Kohama, Atsuhiko Miyata, Zhuo Yang, Rong Yu, and Weiqiang Yu
  • DOI：10.1038/s41535-026-00881

References

  1. Y. Cui et al., npj Quantum Materials 11, 881 (2026).
  2. M. Zhu et al., npj Quantum Materials 10, 74 (2025).
  3. J. Xiang et al., Nature 625, 270 (2024).

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(Published on: Wednesday May 13th, 2026)

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