学术报告（5月21日上午10:30-11:30）

主持人：王猛教授

中子散射系列学术报告之三

报告摘要：

The triangular-lattice antiferromagnet (TLAF) is a prototypical two-dimensional frustrated magnet. If the spin moment is small (S=1/2 or 1), the quantum fluctuation could interfere the spin, electron, lattice and orbitals, and host exotic ground states such as nematic spin-state and chiral liquid phase. A striking example of these quantum phenomena is the transition from a non-collinear 120° spin structure in zero magnetic field into a collinear up-up-down (uud) state in a finite range of applied magnetic field, and the magnetization displays a plateau at one-third of its saturation value M=Ms/3. Although there is an enormous theoretical activity on the origin of those quantum states, the experimental investigation of the spin excitations is still limited. The triple-perovskite, A₃BB’₂O₉, is a typical spin-1/2 TLAF with/without Dzyaloshinskii-Moriya. The magnetic B²⁺ layers are well separated by the non-magnetic clusters of the B’₂O₉ bioctahedra and A²⁺ ions. We have performed elastic and inelastic neutron scattering on this spatially-isotropic antiferromagnet, and observed strong quantum effects in the system. Through detailed comparisons with the linear and nonlinear spin-wave theories, we point out that the large-S approximation is inadequate to explain our experimental observation. Moreover, we have extended the work to the other TLAF of the triple- or multi-perovskite compounds, such as S=1 and 5/2.

个人简介：

  马杰，上海交通大学物理与天文学院特别研究员，博士生导师，美国衣阿华州立大学物理与天文系博士，美国橡树岭国家实验室和田纳西大学物理与天文系博士后。长期从事凝聚态物理前沿实验研究方面的工作，尤其是运用中子散射及同步辐射X光技术对强关联体系功能材料的晶体结构、声子谱和磁子谱进行研究，探讨材料中电子、磁子、声子和轨道等相互作用及其导致的诸如电荷有序、轨道晶格耦合、自旋晶格相互作用等新奇量子效应和物理现象，以及这些效应对功能材料中各种性能的影响。已在Science, Nature Materials, Nature Nanotechnology, Nature Communications, Proceedings of the National Academy, Physical Review Letters, Journal of the American Chemical Society 等国际主流杂志上发表论文46篇。