Strongly Correlated Electron Phenomena in Rare Earth and Actinide Intermetallics

这个实验研究项目的重点是晶体固体的不寻常的电子特性，其中内壳层f电子（存在于稀土和锕系元素中）与外层传导电子处于相同的能量范围。局域电子系统和传导电子系统的杂化导致了与一些尚未完全理解的表现强烈相关的行为。本项目特别感兴趣的不寻常效应是非费米-液体行为；重费米子化合物的超导性和磁性以及小间隙半导体（近藤绝缘体）中由于杂化而形成的小能隙。这些影响将在改变成分、磁场、温度或压力的情况下进行研究。要进行的测量包括热、输运和磁性；在一些合作的情况下，额外的测量将包括中子散射、光电发射、电子隧穿、红外光谱和核磁共振。这个研究项目通过实验研究某些类型的化合物的不寻常行为，这些化合物将重元素（稀土或锕系元素）与轻元素结合，例如金属间金属铀铍13。在这种情况下，来自U的深核电子仍然定位在U位上，但与来自铍的自由电子相互作用，这种相互作用使自由电子或传导电子具有非常特殊的性质。这种效应导致“相关电子”行为和“电子”性质的异常，如导电性、导热性的电子部分、磁化率等。在许多测量中，导电电子的表现就好像它们的质量大大提高了，相对于真空或简单金属（如钠、铜或铝）中的电子质量，提高了三个数量级（因此被称为“重费米子化合物”）。对这些材料及其效应的研究是有价值的，可以作为固体电学和相关特性理论的试验场，然后可以更自信地应用于其他系统；在寻找新特性和新化合物的过程中，它们可能会在技术上找到新的应用。这个研究项目是跨学科的，涉及研究生和本科生，他们将接受良好的培训，进入工业、政府或教育部门的职位。＊＊＊

w:\awards\awards96\num.doc 9705454 Maple This experimental research project focuses on the unusual electronic properties of crystalline solids in which localized inner shell f-electrons (present in rare earth and actinide elements) lie in the same energy range as outer shell conduction electrons. Hybridization of the localized and conduction electron systems leads to strongly correlated behavior with several manifestations which remain incompletely understood. The particular unusual effects of interest in this project are non- Fermi-liquid behavior; superconductivity and magnetism in heavy fermion compounds; and the formation of small energy gaps due to hybridization in small gap semiconductors (Kondo insulators). These effects will be studied under changing composition, magnetic field, temperature or pressure. Measurements to be performed include thermal, transport and magnetic properties; additional measurements, in some cases with collaborations, will include neutron scattering, photoemission, electron tunneling, infrared spectroscopy, and nuclear magnetic resonance. %%% This research project experimentally studies the unusual behavior of certain types of compounds which combine heavy (rare earth or actinide elements) with lighter elements, as for example in the intermetallic metal Uranium Beryllium 13. In this case deep core electrons from U remain localized on the U sites but interact with free electrons from the Beryllium, an interaction that lends very peculiar properties to the free or conduction electrons. This effect leads to "correlated electron" behavior and to anomalies in "electronic" properties, such as the electrical conductivity, the electronic portion of the thermal conductivity, the magnetic susceptibility, and others. The conduction electrons behave in many measurements as if their masses were greatly enhanc ed, by up to three orders of magnitude (hence the name "heavy fermion compound"), relative to the electronic mass in vacuum or in simple metals such as sodium, copper or aluminum. The study of these materials and their effects is valuable as a testing ground for theories of electrical and related properties of solids, which can then be more confidently applied to other systems; and in the search for novel properties and new compounds which may find new application in technology. This research project is interdisciplinary in nature and involves both graduate and undergraduate students who will be excellently trained to enter positions in industry, government or education. ***