金属团簇奇异铁磁、铁电和多铁性的电子关联机制

Experimentally, two magnetic states of metal Fe, Co clusters are found with distinct magnetic moments, polarizabilities, and ionization potentials, indicating distinct valences. The unexpected ferromagnetism and ferroelectricity coexist in Rh, Nb clusters. However neither of these properties is present in the bulk. These discoveries bring both new challenges and opportunities to contemporary quantum many-body theory in finite system. Here, we proposed to carry out studying the strongly electronic correlated effects of ferromagnetism and ferroelectricity in metal clusters by using the density functional theory combined with the dynamical mean field theory (DFT+DMFT) scheme. This scheme is widely used for simulation of the weak and strong correlated effects of metal clusters, such as the spin orbit coupling, Jahn-Teller effect, electron phonon interaction, Mott transformation in a unified theoretical framework. The atomic structures and electronic properties of the cluster ground and metastable states are determined from the first principles DFT electronic structure calculations. By using the Hubbard model, accurately reveal physical nature of the novel ferromagnetism, ferroelectricity , and multiferroic behavior in metal clusters by developing realistic many-body model Hamiltonians and solving the dynamic mean field equations.

实验发现磁性金属Fe、Co等团簇呈现不同的磁矩、极化率、电离势和不同的价态的磁性双态；普通金属Rh、Nb等团簇表现出奇异的多铁性，同时拥有铁电和铁磁两种铁性序，这些性质在块体中并不存在。这些发现给现行的有限体系量子多体理论带来机遇和挑战。本项目采用密度泛函结合动力学平均场理论（DFT+DMFT）方案，研究金属团簇奇异磁性和多铁性的电子关联机制。采用第一性原理DFT计算，确定团簇基态和亚稳态的原子几何结构及基本电子性质。从Hubbard模型出发，用统一的理论框架描述金属团簇中各种可能的弱关联和强关联，包括自旋-轨道耦合、Jahn-Teller效应、电-声相互作用、Mott转变等，结合团簇尺寸和结构特点，构建微观多体模型，求解动力学平均场方程，对团簇的电子结构进行精确的理论计算，揭示团簇奇异磁性和多铁性的物理本质。

发展了一套研究金属团簇奇异铁磁、铁电和多铁性的电子关联的密度泛函结合动力学平均场理论（DFT+DMFT）的方案、技术路径，完成了相关程序编写、调试和测试。研究团簇与二维体系电子关联与量子调控，预言石墨烯（Gr）与强自旋-轨道耦合（SOC）的GaSb体系异质结Gr/GaSb的量子自旋霍尔（QSH）效应，石墨烯和蓝磷 (Gr/BPh)双层带隙和电子结构的压力调控。研究Bi团簇在Cu（111）面生长，发现单层α‑Bi烯的生长规律和多层Bi（110）薄膜的稳定性，Bi团簇和Bi烯在MoTe2表面生长，褶皱的Bi原子在MoTe2表面从小团簇到单层的生长规律和稳定性。内插Sr-Cl-layers的有机钙钛矿 CH3NH3PbI3薄膜的电荷分离与光吸附的完整相图被给出，表明该体系可大大改进可见光区域的光吸收。对Cs3+nPb nSb2I9+3n/GaN钙钛矿异质结的设计和高灵敏光电子响应的系统研究，理论最高能量转换系数可达28.5%。作为一种典型的强关联材料，我们用气相团簇束流沉积装置，成功制备各种衬底的尺寸在5nm以下的单斜晶VO2纳米团簇，通过VO2氢和氧空位共同掺杂，发现新型的金属-绝缘体相变（MIT）。合成一系列四配位Co(II)化合物，发现通过双Cl桥联两个双核化合物表现出双磁弛豫现象。研究单核、双核及多核Dy稀土分子磁体，揭示其内在的磁构效关系及磁弛豫机制，实现空气稳定性单分子磁体的能垒和弛豫时间最大化。通过光控调节一系列Er(III)的单分子磁体的各向异性磁学性质。