Strongly Correlated Electron Phenomena in Rare Earth and Actinide Intermetallics

w:\awards\awards96\num.doc 小行星9705454 这 实验研究项目的重点是结晶固体的不寻常的电子特性，其中局部内壳层f电子（存在于稀土和锕系元素中）与外壳层传导电子处于相同的能量范围。 本地化和 传导电子系统导致强烈相关的行为，具有几种表现形式，这些表现形式仍然不完全理解。 在这个项目中，特别令人感兴趣的不寻常的效应是非费米液体行为;重费米子化合物的超导性和磁性;以及由于小间隙半导体（近藤绝缘体）中的杂化而形成的小能隙。 这些 将研究在改变成分、磁场、温度或压力下的影响。 要进行的测量包括热，输运和磁特性;在某些情况下，与合作，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。 本研究项目通过实验研究了某些类型的化合物的异常行为，这些化合物将重元素（稀土或锕系元素）与较轻的元素结合在一起，例如金属间化合物铀铍13。在这种情况下，来自U的深核电子仍然局限在U位置上，但与来自Berg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“关联电子”行为和“电子”性质的异常，例如电导率、热导率的电子部分、磁化率等。在许多测量中，传导电子的行为就好像它们的质量大大增加了艾德，相对于真空或简单金属（如钠、铜或铝）中的电子质量，增加了三个数量级（因此得名“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性质理论的试验场，然后可以更有信心地应用于其他系统;并在寻找新的性质和新的化合物，可能会发现新的技术应用。 这个研究项目是跨学科的性质，涉及研究生和本科生谁将得到良好的培训，进入行业，政府或教育职位。 ***

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. ***