报告题目 (Title)：New Materials Exploration in Quantum Spin Liquid and Topological Semimetals（量子自旋液体和拓扑半金属的新材料探索）

报告人 (Speaker)：冯子力（日本东京大学）

报告时间 (Time)：2023年7月3日(周一) 14:00

报告地点 (Place)：校本部 E106

邀请人 (Inviter)：任伟 教授

主办部门：理学院物理系

摘要 (Abstract)：

New material exploration is essential for searching for exotic phenomena and extending our understanding of fundamental physics. In this talk, I will mainly talk about our new materials exploration in quantum spin liquid (QSL) and topological semimetals (TSM).

In the first part, by introducing the NMR-friendly element fluorine, we synthesized a new QSL candidate Cu3Zn(OH)6FBr and observed the spin-1/2 spinon excitation providing firm evidence for spin fractionalization in a topologically ordered spin system. Then we built a phase diagram between magnetic ordered Cu4(OH)6FBr and topological order Cu3Zn(OH)6FBr[1-2]. In the second part, since the type of high-energy fermion is limited by Poincare symmetry, new types of fermions without any high-energy counterpart may exist in solid-sate materials. Collaborating with the ARPES group, we observed three fermions in MoP grown by the flux method for the first time, and multiple fermions coexisting in PdBiSe [3-4]. Finally, as a typical transport character in topological magnets, the large anomalous Nernst effect (ANE) was studied. We obtained a recorded ANE signal in polycrystalline topological ferromagnet Fe3Ga alloy by tuning the position of the nodal web. This compound provides a promising candidate for waste heat harvest using ANE [5].

Reference:

[1] Z.L. Feng, W. Yi, et. al. Chin. Phys. Lett. 36, 017502, (2018).

[2] Z.L. Feng, Y. Wei, et. al., Phys. Rev. B 98, 155127, (2018).

[3] B.Q. Lv, Z.L. Feng, Q.N. Xu, et. al. Nature 546, 627-631, (2017).

[4] B.Q. Lv, Z.F. Feng, J.Z. Zhao, et. al., Phys. Rev. B 99, 241104(R) (2019).

[5] Z.L. Feng, S. Minami, et. al., Adv. Funct. Mater. 2206519. (2022)

新材料探索对于寻找奇异现象和扩展我们对基础物理学的理解至关重要。本次报告将主要介绍我们在量子自旋液体（QSL）和拓扑半金属（TSM）方面的新材料探索。在第一部分，我们通过引入核磁共振友好的氟元素，合成了新的QSL候选材料Cu3Zn(OH)6FBr，观察到自旋1/2自旋子激发，为拓扑序自旋系统中的自旋分数化激发提供了可靠证据。然后我们建立了磁性有序Cu4(OH)6FBr和拓扑有序Cu3Zn(OH)6FBr之间的相图。在第二部分，由于高能费米子的类型受限于Poincare对称性，在固态材料中可能存在没有任何高能对应物的新类型费米子。通过与ARPES课题组合作，我们首次在用通量法生长的MoP中观察到三重简并费米子，在PdBiSe中观察到多中新型费米子共存。最后，作为拓扑磁体中的一个典型的输运特征，我们研究了拓扑磁体中的反常Nernst效应。我们通过调整Nodal web的位置，在多晶拓扑铁磁体Fe3Ga合金中获得了记录的ANE信号。这为利用ANE进行废热收集提供了一个有希望的候选材料。