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arXiv · 2504.08570

NMR study of supersolid phases in the triangular-lattice antiferromagnet Na2BaCo(PO4)2

Xiaoyu Xu·Zhanlong Wu·Ying Chen·Qing Huang·Ze Hu·Xinyu Shi·Kefan Du·Shuo Li·Rui Bian·Rong Yu·Yi Cui·Haidong Zhou·Weiqiang Yu
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Abstract

We report ultra-low-temperature $^{23}$Na NMR measurements on the Ising triangular lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$, which precisely resolve the phase diagram under magnetic field applied along the crystalline $c$ axis. With increasing field, the NMR spectra resolve three ordered phases with distinct spin configurations: the Y, up-up-down (UUD), and V phases. The spin-lattice relaxation rate $1/T_1$ data demonstrate gapless excitations in the Y and V phases, strongly supporting their supersolid nature. However, the phase transitions from the UUD phase to the two supersolid phases exhibit dramatically different behaviors upon cooling. Prior to entering the Y phase, $1/T_1$ identifies a gapless regime within the UUD phase, suggesting a Berezinskii-Kosterlitz-Thouless phase above a second-order phase transition. In contrast, the coexistence of the UUD and V phases observed in our experiments provides direct evidence of a first-order phase transition between these phases.

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Xiaoyu Xu, Zhanlong Wu, Ying Chen, Qing Huang, Ze Hu, Xinyu Shi, Kefan Du, Shuo Li, Rui Bian, Rong Yu, Yi Cui, Haidong Zhou, Weiqiang Yu. 2025-04-11. NMR study of supersolid phases in the triangular-lattice antiferromagnet Na2BaCo(PO4)2. https://doi.org/10.1103/gsk8-1k9q

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