Abstract
Discovery of new states of matter is a key objective in modern condensed matter physics, which often leads to revolutionary technological advancements such as superconductivity. Quantum spin nematic, a "hidden order"that evades conventional magnetic probes, is one such state. Na2BaNi(PO4)2 is a potential spin nematic material, suggested by the observation of a two-magnon Bose-Einstein condensation from above the saturation field. However, direct confirmation of the spin nematicity remains elusive. This Letter presents inelastic neutron scattering spectra from the putative spin nematic phases of Na2BaNi(PO4)2, revealing low-energy quadrupole waves that are absent in the neighboring conventional magnetic phases. A spin-one model quantitatively captures the full details of the spin excitation spectra across all low-temperature phases, providing direct evidence of the spin nematic orders. Additionally, we show evidence of the three-magnon continuum and two-magnon bound states in the 1/3-magnetization plateau, revealing condensation of the two-magnon bound state as the origin of the low-field spin nematic supersolid phase.
| Original language | English |
|---|---|
| Article number | 156704 |
| Journal | Physical Review Letters |
| Volume | 135 |
| Issue number | 15 |
| DOIs | |
| State | Published - Oct 10 2025 |
Funding
We thank Hai-Qing Lin, Qingming Zhang, Chao Cao, and Ziji Xiang for helpful discussions. This work was supported by the National Key Research and Development Program of China (Grants No. 2021YFA1400400, No. 2021ZD0301800, No. 2022YFA1402200, and No. 2024YFA1408303), the National Natural Science Foundation of China (Grants No. 12134020, No. 12034017, No. 12104255, No. 12322403, No. 12347107, No. 12374124, No. 12374146, No. 12374150, No. 12488201, No. 12494592, and No. 12574157), the Strategic Priority Research Program of Chinese Academy of Sciences (Grants No. XDB0500202 and No. XDB33000000), the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2021004), the Key R&D Program of Zhejiang Province, China (Grant No. 2021C01002), the Guangdong Provincial Quantum Science Strategic Initiative (Grants No. GDZX2401006 and No. GDZX2401007), and the Fundamental Research Funds for the Central Universities (Grant No. 226-2024-00068). We also acknowledge the neutron beam time awarded by Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex (J-PARC) through Proposal No. 2024A0351. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory, where the beam time was allocated to CNCS on Proposal No. IPTS-29333.