Electron hybridization phenomena in Yb- and Eu-based heavy-fermion systems

Yb 和 Eu 基重费米子系统中的电子杂化现象

• 批准号: 115998015
• 负责人: Privatdozent Dr. Christoph Geibel
• 金额: --
• 依托单位: Max-Planck-Institut für Chemische Physik fester Stoffe (MPI CPfS)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2009
• 资助国家: 德国
• 起止时间: 2008-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/115998015?language=en
• 关键词: Electron; hybridization; phenomena; Yb; Eu

The main driving force of electron-correlation phenomena in rare-earth (RE) intermetalliccompounds are interactions of localized 4f and delocalized valence electrons. Uponincreasing the interaction strength, the ground state of these systems evolves from magneticorder via spin polarisation of the itinerant electrons (RKKY interaction) over screening of the 4fmagnetic moments (Kondo effect) to mixed-valent behavior (MV). Thereby a periodicarrangement of the 4f Kondo impurities (Kondo lattice) causes heavy-fermion (HF) propertiescharacterized by narrow hybrid bands with effective masses that are 1000 times larger thanthe free electron mass, me. Such systems attract a very vivid interest, since they are in aregime where electronic and magnetic subsystems are strongly coupled with each otherleading to a variety of fascinating quasi-particle phenomena. The possibility to tune thehybridization strength allows to explore quantum-phase transitions in detail.Subject of this project is a detailed investigation of the interactions of 4f and conductionelectrons in Yb- and Eu-based systems in the vicinity of quantum-phase transitions frommagnetically ordered to non-ordered ground states. Final goal is the understanding of therelation between electron spectroscopic results and the thermodynamic and transportproperties observed in these systems. Since the correlation properties depend crucially onhybridization of 4f and valence-band states, tuning is achieved by changing the relativeenergy positions of the bands with respect to those of the 4f states by means of alloying andoverlayer deposition. The project comprises the preparation and structural characterization ofrespective single crystalline samples, the determination of their low-energy excitationproperties like specific heat, magnetization and electrical conductivity and the electronspectroscopic investigation by means of ultra-high energy (down to 1 meV) and momentum(better than 0.01 1/Å) resolution photoemission. The obtained data will be analysed in theframework of a recently developed approach to the periodic Anderson model (PAM).

稀土金属间化合物中电子关联现象的主要驱动力是定域4f和离域价电子的相互作用。随着相互作用强度的增加，系统的基态由巡游电子的自旋极化（RKKY相互作用）、4f磁矩的屏蔽（Kondo效应）的磁有序演化为混合价态（MV）。因此，4f近藤杂质（近藤晶格）的无序排列导致重费米子（HF）性质，其特征在于具有有效质量比自由电子质量me大1000倍的窄混合带。这样的系统吸引了非常生动的兴趣，因为它们处于电子和磁子系统相互强烈耦合的区域，导致各种迷人的准粒子现象。本项目的主要内容是详细研究Yb和Eu基系统中4f和导电电子在从磁有序到无序基态的量子相变附近的相互作用。最终的目标是理解电子光谱结果和在这些系统中观察到的热力学和输运性质之间的关系。由于相关性质在很大程度上取决于4f和价带态的杂交，因此可以通过合金化和层间沉积改变能带相对于4f态的相对能量位置来实现调谐。该项目包括各个单晶样品的制备和结构表征，确定它们的低能激发特性，如比热、磁化强度和电导率，以及通过超高能量（低至1 meV）和动量（优于0.01 1/m3）分辨率光电发射进行电子光谱研究。所获得的数据将在最近开发的周期性安德森模型（PAM）的框架内进行分析。