学术报告（ 2026年3月13日10:10）：Spin Supersolid on a Triangular Lattice: Spin Dynamics, Magnetic Cooling, and Spin Seebeck Effect

主 持 人：姚道新 教授

报告摘要：Supersolid is an exotic quantum state of matter that emerges near absolute zero temperature. The spin supersolid spontaneously breaks both the lattice translational and spin rotational symmetries, forming a quantum magnetic analog of supersolid. Recently, using tensor network approaches [1], we determined the microscopic spin Hamiltonian of a Co-based quantum antiferromagnet Na2BaCo(PO4)2. We discovered that it represents a rare and nearly perfect realization of the easy-axis triangular lattice Heisenberg model, and therefore supports the long-sought spin supersolid state [2]. Through theoretical prediction and subsequent experimental collaboration, we observed a giant magnetocaloric effect (MCE) arising from the highly fluctuating spin state - a phenomenon we term spin supersolid cooling [3]. Neutron scattering and numerical studies of the spin dynamics [4] have identified rich low-energy excitations responsible for the giant MCE. Furthermore, using thermal tensor networks, we further show that these dissipationless excitations support a spin supercurrent - measurable via the spin Seebeck effect [5] - which represents a key quantum transport characteristic of spin supersolid. Beyond insulating systems, we have recently found that the spin supersolid can also exist in metals. We establish an RKKY-dipolar theory that describes the emergence of such a state in metallic compounds [6].

References:

[1] Q. Li, Y. Gao, Y.-Y. He, Y. Qi, B.-B. Chen, WL, Tangent Space Approach for Thermal Tensor Network Simulations of the 2D Hubbard Model. Phys. Rev. Lett. 130, 226502 (2023).  

[2] Y. Gao, Y. Fan, H. Li, [...], Y. Wan, WL. Spin supersolidity in nearly ideal easy-axis triangular quantum antiferromagnet Na2BaCo(PO4)2. Npj Quantum Mater. 7, 89 (2022).

[3] J. Xiang, C. Zhang, Y. Gao, [...], W. Jin, WL, P. Sun, G. Su, Giant magnetocaloric effect in spin supersolid candidate Na2BaCo(PO4)2, Nature 625, 270 (2024).

[4] Y. Gao, C. Zhang, [...], W. Jin, G. Su, and WL, Double magnon-roton excitations in the triangular-lattice spin supersolid, Phys. Rev. B 110, 214408 (2024).

[5] Y. Gao, Y. Huang, S. Maekawa, WL, Spin Seebeck Effect of Triangular-lattice Spin Supersolid, Phys. Rev. Lett. 135, 236504 (2025).

[6] M. Shu, X. Xu, [...], WL, J. Ma, Z. Qu, Giant Magnetocaloric Effect and Spin Supersolid in a Metallic Dipolar Magnet, Nature 651, 61 (2026).

报告人简历：李伟，中国科学院理论物理研究所研究员，从事强关联多体计算与量子磁性理论研究。发表学术论文90余篇，其中包括Nature、PRL等国际重要期刊论文。近年来，在有限温度张量网络方法发展及其关联量子系统应用中取得系列进展，成果“三角晶格自旋超固态及其巨磁卡效应”先后入选“2024年中国十大科技进展新闻”和“2024年度中国科学十大进展”。获基金委青年人才项目、中科院引才计划资助；担任中科院—财政部基础研究青年团队负责人、中科院先导专项负责人。任CPL等四刊青年编委、CTP编委。2025年获中国科学院青年科学家奖。