【报告题目】Determining the range of magnetic interactions from the relations between magnon eigenvalues at high-symmetry k points
【报 告 人】万贤刚教授，南京大学
【报告时间】11月12日（周五），14:00-15:30
【腾讯会议ID】548318572
【报告摘要】Magnetic exchange interactions (MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results. But how many MEIs need to be included in the fitting process for a material is not clear a priori, which limits the quality of results obtained by these conventional methods. In this paper, based on linear spin-wave theory but without performing matrix diagonalization, we show that for a general quadratic spin Hamiltonian, there is a simple relation between the Fourier transform of MEIs and the sum of square of magnon energies (SSME). We further show that according to the real-space distance range within which MEIs are considered relevant, one can obtain the corresponding relationships between SSME in momentum space. We also develop a theoretical tool for tabulating the rule about SSME. By directly utilizing these characteristics and the experimental magnon energies at only a few high-symmetry k points in the Brillouin zone, one can obtain strong constraints about the range of exchange path beyond which MEIs can be safely neglected.
【报告人简介】万贤纲，南京大学物理系教授，近年来关于5d过渡金属氧化物奇异物理研究的一系列原创性工作受到了同行的广泛关注，特别是在实际材料中发现Weyl半金属和Axion绝缘体以及在掺杂拓扑绝缘体中实现电声子耦合导致的非常规超导；关于Weyl半金属的工作被Science的前瞻文章评价为“(凝聚态领域)一个新的前沿”。相关论文发表在Nature, Nature Communications, Phys. Rev. Lett., Phys. Rev. B等国际著名期刊上。获2014年度香港大学Daniel Tsui (崔琦) Fellowship，2019年“科学探索奖”，2020年第二届全国创新争先奖，基于其研究成果的报导：《最新研究表明自然界中约 24% 的材料可能具有拓扑结构》入选 2019 年度中国十大科技进展新闻。
【邀请人】高先龙 教授
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