Quantum Criticallity and Magnetic Semiconductors

量子临界性和磁性半导体

• 批准号: 0406140
• 负责人: John DiTusa
• 金额: $ 34.5万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2007-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0406140&HistoricalAwards=false
• 关键词: Quantum; Criticallity; Magnetic; Semiconductors

This condensed matter physics project will investigate metallic materials that exhibit "non-Fermi-liquid" properties. The defining behavior in terms of conductivity et al., is frequently found near zero temperature magnetic phase transitions and quantum critical points. However, little is known about the effect of disorder and low carrier density associated with a nearby metal-to-insulator (MI) transition. Of interest is the incipient metallic state that is correlated with itinerant magnetism. This will be probed via experiments in silicides, germanides, and sulfides in proximity to magnetic and/or MI transitions. Transport, magnetic, optical, and thermodynamic properties will be determined in these materials, which have been chosen so that variations in carrier densities and disorder will allow access to interesting quantum critical points. The experiments address three questions: (A) Is the non-Fermi-liquid behavior discovered in strongly fluctuating metals a crossover effect, or does this behavior signal the formation of a novel ground state? (B) What effect does the disorder and low carrier concentration associated with a nearby MI transition have on the properties of materials near quantum critical points? and, (C) Are there room temperature semiconducting and ferromagnetic phases among the solid solutions of transition metal silicides or Kondo insulators that may have technological uses? Undergraduate, graduate and postdoctoral students, as well as Teach for America participants will be take part in cutting edge research and training that will prepare them for careers in academe, industry and government..Many recent experiments have shown that the temperature for which a transition to a magnetically ordered state occurs can be varied with either a change in chemical composition of the material or the application of external pressure. For a variety of magnetic systems this transition temperature can be driven downward until it is essentially at the absolute zero of temperature. The key discovery is that when the transition temperature is close to zero, the physical properties, such as the response to electric and magnetic fields and thermal energy, change such that they differ from any found in a century of research in solids. Although progress has been made toward understanding these "quantum critical" phenomena, many mysteries remain, including the range of temperatures and chemical compositions where these physics dominates the behavior of materials. This project focuses on a particular category of magnetic systems, magnetic semiconductors, where the physics of quantum criticality can be investigated. This is of particular importance since, for example, new technologies based on magnetic semiconductors have been under development, yet their physical properties have not been fully explored. This proposal contributes to the development and training of undergraduate, graduate and post-doctoral students. Teach for America participants will be recruited to take part in the research, which involves collaborations with faculty at Southern University, an HCBU, and with faculty in Europe and Southern Africa.

这个凝聚态物理项目将研究具有“非费米液体”性质的金属材料。电导率等方面的定义行为经常出现在零温磁相变和量子临界点附近。然而，人们对附近金属到绝缘体(MI)转变的无序和低载流子密度的影响知之甚少。令人感兴趣的是与巡回磁性相关的初始金属状态。这将通过在靠近磁性和/或MI转变的硅化物、锗化物和硫化物中进行实验来探索。这些材料的输运、磁性、光学和热力学性质将被确定，这些材料的选择使得载流子密度和无序的变化将允许访问有趣的量子临界点。这些实验解决了三个问题：(A)在强烈波动的金属中发现的非费米液体行为是一种交叉效应，还是这种行为标志着一种新的基态的形成？(B)与附近的MI跃迁相关的无序和低载流子浓度对量子临界点附近的材料的性质有什么影响？以及，(C)过渡金属硅化物或近藤绝缘体的固溶体中是否存在可能具有技术用途的室温半导体和铁磁性相？本科生、研究生和博士后，以及为美国而教的学生将参加尖端研究和培训，为他们在学术界、工业界和政府的职业生涯做准备。最近的许多实验表明，发生向磁性有序状态转变的温度可以随着材料化学成分的变化或外部压力的作用而变化。对于各种磁性系统，这一转变温度可以被降低，直到它基本上处于绝对零度。关键的发现是，当转变温度接近零时，物理性质，如对电场、磁场和热能的响应，会发生变化，以至于它们与一个世纪以来对固体的研究中发现的任何东西都不同。尽管在理解这些“量子临界”现象方面已经取得了进展，但仍然有许多谜团，包括温度范围和化学成分，在这些温度和化学成分中，这些物理因素主导着材料的行为。这个项目专注于一类特殊的磁性系统，磁性半导体，在那里可以研究量子临界性的物理。这一点特别重要，因为例如，基于磁性半导体的新技术正在开发中，但其物理特性尚未得到充分探索。这一建议有助于本科生、研究生和博士后的发展和培养。为美国而教的参与者将被招募参加这项研究，该研究涉及与南方大学、哥伦比亚大学和非洲南部的教师合作。