4月24日德国著名科学家Khomskii教授学术报告：Orbital-selective effects in transition metal compounds: “molecules” in solids against magnetism

报告时间： 2017年4月24日（周一）上午10：00

报告地点：唐仲英楼A313

报告题目：

Orbital-selective effects in transition metal compounds: “molecules” in solids against magnetism

Abstract：Close to Mott transition several novel states can appear. In particular, “molecular clusters” can be formed in the solid, such as dimers, trimers, etc. In my talk I will illustrate such phenomena, especially dimer formation, on many examples (pyroxenes; La4Ru2O10; Li2RuO3; M1 and M2 phases of VO2; V and Cr hollandites). The concept of orbital-selective Peierls transitions will be proposed and justified. In systems containing structural metal dimers there may exist in the presence of different orbitals a special state with partial formation of singlets by electrons on one orbital, while others are effectively decoupled and may give e.g. long-range magnetic order or stay paramagnetic. Similar situation can be realized in dimers spontaneously formed at structural phase transitions, which can be called orbital-selective Peierls transition. This can occur in case of strongly nonuniform hopping integrals for different orbitals and small intra-atomic Hund's rule coupling JH . Yet another consequence of this picture is that for odd number of electrons per dimer there exist competition between double exchange mechanism of ferromagnetism, and the formation of singlet dimer by electron on one orbital, with remaining electrons giving a net spin of a dimer. The first case is realized for strong Hund's rule coupling, typical for 3d compounds, whereas the second is more plausible for 4d-5d compounds. We discuss some implications of these phenomena, and consider examples of real systems, in which orbital-selective phase seems to be realized.

Khomskii教授在关联电子系统、金属绝缘体转变、磁性、轨道序、超导等多个领域做出了杰出的工作。他和合作者提出的Kugel-Khmoskii模型在轨道序方面产生了重大的影响。Khomskii教授共发表论文200余篇（含PRL40多篇），被他人引用10000多次。

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