摘要

Using density functional based LDA+U method and linear-response theory, we study the magnetic exchange interactions of the superconductor Nd1-xSrxNiO2. Our calculated nearest-neighbor exchange constant J1=82 meV is large, weakly affected by doping and is only slightly smaller than that found in the sister compound CaCuO2. We however find that the hole doping significantly enhances the inter-layer exchange coupling as it affects the magnetic moment of the Ni-3d{3z2-r2} orbital. This can be understood in terms of small hybridization of Ni-3d{3z2-r2} within the NiO2 plane which results in a flat band near the Fermi level, and its large overlap along z direction. We also demonstrate that the Nd-5d states appearing at the Fermi level, do not affect the magnetic exchange interactions, and thus may not participate in the superconductivity of this compound. Whereas many previous works emphasize the importance of the Ni-3d{x2-y2} and Nd-5d orbitals, we instead propose that the material can be described by a Ni-3d{x2-y2}/Ni-3d{3z2-r2} two-band model. Its solution is studied here on the level of Dynamical Mean Field Theory and reveals an underlying Mott insulating state which, depending on precise values of the intra-atomic Hunds coupling, produces upon doping competing S=0 and S=1 two-hole states at low energies that lead to very different quasiparticle band structures. We propose that trends upon doping in spin excitational spectrum and quasiparticle density of state can be a way to probe Ni 3d8 configuration.

报告人简介

万贤纲，南京大学物理学院教授，1990年至2000年在南京大学学习，获得学士、硕士、博士学位。2001起在南京大学历任讲师，副教授，2010年任教授。主要学术成绩为：提出了新型拓扑量子态—Weyl 半金属，引发了国际上Weyl 半金属的研究热潮；发展了一套计算磁性相互作用的方法并确定多个复杂体系的基态磁构型；基于原子绝缘体基组发展了高效判断拓扑性能的理论方法，并用其对无机材料数据库里面所有非磁材料的拓扑特性进行了分类。

获得2014年度香港大学Daniel Tsui Fellowship。2015年获得国家杰出青年科学基金；2016年被评为教育部国家高层次人才特聘教授。获中国物理学会2018-2019年度叶企孙物理奖。2019年获首届腾讯基金会“科学探索奖”。获2019年南京大学突出贡献奖。2020年获第二届全国创新争先奖。