金属Ce的电子结构与γ-α相变机制:理论模型的发展及借助角分辨光电子能谱的实验研究进展  

Electronic Structure and γ-α Phase Transition Mechanism of Cerium: a Review of Theoretical Models and Experimental Researches Using Angle-resolved Photoemission Spectroscopy

作　　者：段煜 罗学兵 张云[1] 张文[1] 冯卫[1] 郝群庆 罗丽珠[1] 刘琴[1] 陈秋云[1] 谭世勇[1] 朱燮刚 赖新春[1] DUAN Yu;LUO Xuebing;ZHANG Yun;ZHANG Wen;FENG Wei;HAO Qunqing;LUO Lizhu;LIU Qin;CHEN Qiuyun;TAN Shiyong;ZHU Xiegang;LAI Xinchun(Institute of Materials,China Academy of Engineering Physics,Mianyang 621908)

机构地区：[1]中国工程物理研究院材料研究所

出　　处：《材料导报》2019年第19期3313-3321,共9页Materials Reports

基　　金：科学挑战计划专题(TZ2016004);国家重点基础研究发展计划项目(2015CB921303);中物院院长基金(201501040)~~

摘　　要：含f电子的镧系和锕系元素是元素周期表中最复杂的成员,他们常常表现出奇异的物理特性。其中最简单而具代表性的就是金属Ce的γ-α相变,该相变不仅晶体结构保持面心立方(fcc)不变,而且伴随有约15%的体积塌缩和磁性变化(γ-Ce为遵循Curie-Weiss定理的顺磁体,而α-Ce具有Pauli顺磁性)。多年来,大量理论和实验研究都致力于理解这一奇特相变的微观机制,理论上曾提出了三种解释该相变的模型,包括跃迁模型(Promotional model)、类Mott转变模型和Kondo模型。其中跃迁模型已因与实验结果不符而被摈弃,而类Mott转变模型主要强调f-f电子的相互作用在相变过程中的变化,Kondo模型则强调相变过程中4f电子与传导电子间相互作用的变化,此二者都在不断发展,至今仍无定论。目前学界基本认同Ce的γ-α相变的奇特性与其特殊电子结构有关。Ce的外层电子结构为4f 15d 16s 2,其中4f电子在实空间是局域,但其能级与价带的5d和6s电子能级的能量接近,造就了4f电子的局域-巡游双重特性,故外界环境的微小变化可能会大大改变Ce的电子结构,进而影响其宏观物理性质。如今,分子束外延技术(MBE)的应用实现了高质量Ce单晶薄膜的制备,结合先进的角分辨光电子能谱(ARPES)可以对Ce的电子结构进行直接观察,便于探究Ce的γ-α相变过程中4f电子的行为,并以此进一步探讨其相变微观机制。此外,Kondo模型具有光电子能谱(PES)可见的特征,且在单杂质安德森模型(SIAM)框架下采用相关计算方法(GS、LDA+U、DMFT等)对Ce的PES特征的理论解释也已较成功地实现,因此Kondo模型逐渐成为目前较为流行的Ce的γ-α相变机制。本文首先简要回顾了Ce的γ-α同构相变的三个主要理论模型,即跃迁模型(Promotional model)、类Mott转变模型和Kondo模型的物理图像及部分实验证据;然后介绍了高质量Ce单晶薄膜的制备方法,并重点分析总�Lanthanides and actinides containing f-electrons are the most complex members of the periodic table,and tend to exhibit peculiar macroscopic physical properties,among which the γ-α phase transition in cerium is one of the most typical representatives.This iso-structual phase transition involves both a volume collapse of more than 15% and the magnetic properties transition from Curie-Weiss like to Pauli-like paramagnetism.Over the years,a variety of theoretical and experimental researches have been dedicated to understand the microscopic mechanism of the γ-α phase transition in cerium,and three main theoretical models were proposed to interpret this phase transition,i.e.promotional model,Mott-like transition model and Kondo model.Among them,the promotional model has faded out for discrepancies with experimental results.On the other hand,both Mott-like model which emphasizes the f-f electrons interaction during the phase transition and Kondo model which values the interaction between 4f electrons and conduction electrons have acquired intensive research efforts,and their validities are still unsettled. However,there has been a consensus that the peculiarity of γ-α phase transition in cerium is related to its unusual 4f electronic structure.The outer electronic configuration of cerium is 4f 15d 16s 2,in which the 4f electrons are localized but are similar in energy level with the 5d and 6s electrons,resulting in the dual characteristics (localization and itinerancy) of the 4f electrons.Therefore,a slight change of the chemical environment can lead to significant change in electronic structure of cerium and alter its macroscopic physical properties. Nowadays,researchers have successfully prepared high-quality cerium single crystal films by applying the technology of molecular beam epitaxy (MBE).Moreover,the electronic structure of Ce can be directly observed by angle-resolved photoemission spectroscopy (ARPES),enabling us to easily study the behavior of 4f electrons during γ-α phase transition.It's worth noti

关 键 词：金属Ce 单晶薄膜 电子结构 γ-α相变 理论模型 Kondo模型 f电子 角分辨光电子能谱(ARPES) 

分 类 号：O469[理学—凝聚态物理]