重费米子体系中磁性与近藤效应及相图的理论研究

The heavy-fermion compounds possess a variety of phases, and the issue concerning the properties and the parameter regions of these phases, particularly the phase transitions among them continuously focuses attention. In this project, by the application of a optimized mean-field approach on the Kondo lattice model, we plan to give a detailed description of the phases caused by the interplay of magnetism and Kondo screening effect in heavy-fermion systems, and corresponding phase transitions among them, to derive the zero-temperature and finite-temperature phase diagrams. The parameter regions and characteristics of the ferromagnetic phase, the antiferromagnetic phase, the Kondo paramagnetic phase, the ferromagnetic heavy-fermion phase, and the antiferromagnetic heavy-fermion phase in heavy-fermion systems are studied as functions of the Kondo coupling, conduction electron filling factor, and conduction electron hopping strength, then the global zero-temperature and finite-temperature phase diagrams are determined. We also calculate the neutron-scattering distributions of these phases, which are expected to help distinguishing the phases through future neutron-scattering experiments. This project is expected to improve the theoretical understanding of the phases and corresponding phase transitions in heavy-fermion systems, and may provide further support in studying other phases, e.g., superconducting phase.

重费米子化合物呈现出多种物相，而各物相的存在条件和性质、物相之间的相变特征成为理论研究的重要问题。本项目基于近藤晶格模型，利用优化的平均场理论，研究重费米子化合物中因磁性和近藤效应的相互竞争而导致的各种物相的存在区域及各物相间的相变，得到体系的零温及非零温相图。拟研究随传导电子填充数、近藤耦合强度、传导电子最近邻和次近邻跃迁系数的变化，重费米子化合物中铁磁相、反铁磁相、近藤顺磁相、铁磁重费米子相、反铁磁重费米子相的存在区域及其性质，分析物相之间的相变特征，从而给出重费米子化合物在填充数和近藤耦合强度连续变化时的全空间基态相图及有限温相图；研究各物相的中子散射强度分布，对利用中子散射实验来分辨各物相的实验方法提供理论依据。本研究预期将丰富对重费米子化合物中各种物相及其转化关系的认识，并可能对重费米子化合物中其他物相（例如超导相等）的研究提供有力的理论支持。

重费米子体系中磁性关联与近藤效应的相互作用将产生丰富的物相和相变过程。本项目基于近藤晶格模型、Anderson晶格模型，采用平均场近似、量子蒙特卡洛模拟、动力学平均场等方法，首先研究了重费米子体系中磁有序与近藤屏蔽效应的竞争和共存，得到了近藤顺磁相、磁有序相、磁有序-近藤屏蔽共存相的存在参数区域，得到了体系的零温与非零温相图；发现在磁性阻挫的影响下，体系将出现更丰富的物相与量子相变过程。特别地，在拓扑型重费米子体系---拓扑性近藤绝缘体中，磁性关联与近藤屏蔽效应的竞争将产生反铁磁相变，导致奇异物相---时间反演对称破缺的反铁磁拓扑绝缘相的出现，并且它可与常规反铁磁相之间发生相变；而在近藤顺磁相中，发现了四种强拓扑绝缘相和两种弱拓扑绝缘相，并得到了包含这些物相的拓扑相图。本项目的系列研究成果将加深对重费米子体系中磁性关联与近藤效应的相互作用过程、以及物相与相变的理论理解。