Quantum spin liquids (QSLs) represent a novel state of matter  in which no spontaneous symmetry is broken and the spins remain in the  liquid-like state even at absolute zero temperature. They hold great potentials  in quantum computation and communication. Furthermore, it is believed that the  understanding of QSLs may help solve the long-term puzzle of high-temperature  superconductivity. For these reasons, QSLs have been studied extensively in the  past 45 years, but so far there still appear to be no ideal QSL  materials.

In this talk, I will  present our results on two types of QSL candidates, geometrically-frustrated  compounds YbMgGaO4 and YbZnGaO4 with the triangular lattice, and a Kitaev  material alpha-RuCl3 with the honeycomb lattice. For both YbMgGaO4 and YbZnGaO4,  we find that their true ground states to be spin glasses, and disorder is mainly  responsible for the spin-liquid-like observations [1]. For alpha-RuCl3, we show  that there is a dominant Kitaev interaction in the zigzag order state [2], and a  magnetic field can drive the system from an ordered state into a possible QSL  state [3,4].

In the end, I will also  briefly discuss our recent discovery of topological magnons in a  three-dimensional antiferromagnet Cu3TeO6 [5].

References:

1, Phys. Rev. Lett. 120,  087201 (2018).

2, Phys. Rev. Lett. 118,  107203 (2017).

3, Phys. Rev. Lett. 119,  227208 (2017).

4, Phys. Rev. Lett. 120,  067202 (2018).

5, Nature Commun. 9, 2591  (2018). 

报告人简介：

南京大学物理学院教授、博导，国家优秀青年基金、江苏杰出青年基金获得者。2005年清华大学本科毕业；2010年纽约州立大学石溪分校博士毕业；2010年至2012年加州大学伯克利分校博士后；2013年被聘为南京大学教授、博导。长期从事电子强关联材料，特别是铜、铁基等高温超导材料、量子自旋液体与拓扑量子材料的单晶生长及中子散射研究。已在Science、Nature及其子刊、PRL等学术期刊发表论文100多篇，总引用次数3000多次。