过渡金属氧化物重费米子体系CaCu3Ru4O12内禀特性和非费米液体行为的研究

Heavy fermion system is an important area of strong correlation electron materials, d-electron transition metal oxides is a new branch of heavy fermion system. Compared with traditional f electron heavy fermion systems, scientists have explored small area of d electron heavy fermion systems. There are many fundamental scientific puzzles needed to be clarified, for instance, the effective mass of d electron heavy fermion systems is rather low compared with f electron heavy fermion system, and the mechanism of enhanced mass is still controversial. CaCu3Ru4O12 is a novel d-electron transition metal oxide. It's a A-site ordered perovskite compound, with simple structure, as well as stable valence state and separate occupying of elements, which is similar to f electron heavy fermion systems. So，the research on physical properties of CaCu3Ru4O12 will deepen the understanding of whole heavy fermion systems. This project plans to study the following aspects of CaCu3Ru4O12 by mean of first principle simulation and experimental measurements. First of all, we will try to discuss the intrinsic mechanism for its enhanced mass by clarifying that Cu2+ and Ru4+ ions are itinerant or localized; secondly, we will attempt to increase the enhanced mass by doping various ions based on multichannel Kondo effect theory; after that, we will study the variant law of various physical quantity, related to heavy fermion intriguing properties, versus doping, crystalline field and pressure, so that we may figure out the universal intrinsic properties of heavy fermion systems irrelevant with above factors and specific materials; finally, we will investigate the behaviors of non-Fermi-liquids and quantum critical point, and give the phase diagram and the ground state properties of relevant compounds.

重费米子HF体系是强关联电子体系的重要研究领域，过渡金属d 电子重费米子体系是HF材料的一个新的分支，人们对d 电子HF材料的认识刚刚起步，尚有有效质量相对较低、HF特征行为原因不明等许多基本的科学问题需要探讨。CaCu3Ru4O12是近年来发现的一类新型过渡金属d 电子HF体系，其结构简单、各元素价态稳定、占位分离，与大多数f电子HF体系具有多种相似性，对其物理特性的研究，将会有助于加深人们对HF体系的认识。本课题将利用第一性原理计算和实验测量相结合的方式，从澄清Cu2+与Ru4+的局域或巡游行为入手，探讨其HF奇异特性的内禀起源；根据多重 Kondo效应的思路，通过掺杂探索提高体系的有效质量；在此基础上，考察与奇异行为相关的各类物理量随掺杂、晶体场和外压力场的变化规律，探求与具体材料无关、体系HF行为普适的内禀特性；考察体系的非费米液体以及量子临界行为，给出相图及各类基态特征。

本课题主要基于重费米子体系的相关研究，重费米子体系是强关联电子体系的重要研究领域，如何控制和改变体系的有效质量、重费米行为原因不明等许多基本的科学问题需要探讨。本项目中我们主要针对d电子CaCu3Ru4O12体系开展了以下工作：成功制备了高质量大尺寸CaCu3Ru4O12单晶及系列Fe掺杂单晶，进行系列物性测试，证实CaCu3Ru4O12是一个重费米子系统；磁性元素(Fe & Co)的B位掺杂可有效提高系统的有效质量；对Fe掺杂样品的交流磁化率和直流磁性驰豫测试证明体系的基态是自旋玻璃态；对CaCu3Ru4O12进行A位非磁性元素和磁性元素掺杂研究发现，Zn掺杂对体系的有效质量基本没有影响，掺杂样品低至2K仍维持费米液体特性，未见基态改变。Ni掺杂对CaCu3Ru4O12电子有效质量的影响是非单调的。稀释A位的Cu一方面破坏了近藤晶格，另一方面减少了Cu dxy带队D（Ef）的贡献。这是影响体系重费米子特性的主要机制; 研究了强自旋轨道耦合体系钒氧化物轨道序对反铁磁二级相变和临界行为的影响; 研究了完全自旋极化磁性半导体CrO2的制备及其相关磁性；研究了氧空位浓度及分布对完全极化磁性半导体CrO2电子结构的影响；同时，我们还开展进行了几种拓扑特性热电材料的研究。