Giant Physical Response in Multi-scale Inhomogeneous Oxides

这项建议着重于在功能氧化物中发现的微观电子/磁性/结构不均匀性，以及它在这些材料的宏观物理响应中所起的相应作用，如磁阻、磁导率、压电常数以及线性和/或非线性光学特性。了解和控制非均匀性和物理响应之间的相互关系对于开发新的先进的电子和磁性设备是至关重要的。热力学或量子临界性、软模、无序效应和电子相分离等概念对于理解相空间中相邻相的共存或涨落具有重要意义。该计划设想的活动包括几类重要的复合氧化物材料。第一个主题是磁阻材料领域(如CuIr2S4-CuCr2S4和(Bi，Sr)MnO_3-(La，Sr)MnO_3)，显示出电荷有序绝缘相和铁磁-金属相之间的竞争和共存。其他主题包括铁电弛豫体(PMN-PT)在MPB附近的增强压电响应和几何受阻反铁磁体(如ZnCr2O4)中的化学压力效应。我们还将研究多晶薄膜中的隧道磁阻以及双钙钛矿结构(Ca，Sr，Ba)Fe0.5Mo0.503的三层结构。该项目的成功将关键取决于对功能性复合氧化物(或硫化物)的全面表征以及高质量多晶材料和单晶的制造。材料合成和经典表征，包括磁输运、磁化率和热力学测量，将在罗格斯大学的PI实验室进行。此外，X射线散射、中子散射、透射电子显微镜、微波、拉曼和低温扫描隧道显微镜实验将通过机构间合作进行。这项研究将在学生的帮助下进行，学生将因此为进入工业、政府或学术界的科学/技术职业做好准备。当材料暴露在诸如磁场或电场、压力或光照射等外部参数下时，现代电子和磁性设备通常利用材料的物理响应。最近的研究表明，在具有微观电/磁/结构不均匀的材料中，磁阻、压电性或线性和/或非线性光学响应等大尺度物理响应可以显著增强。因此，在微观上不均匀的材料中这种增强的响应可以为未来的技术提供科学基础。在这个项目中，我们专注于理解和控制微观非均质性和宏观物理响应之间的相互关系。这种不均匀性可能与不同的电荷/自旋/轨道自由度有关，并且除了静态空间涨落外，还可能伴随动态涨落。我们将主要研究功能复杂的氧化物和其他硫族化合物，显示出各种竞争或相互拮抗的基态。这一项目的成功将关键取决于对材料的全面表征以及高质量多晶材料和单晶的制造。材料的制作和基本表征将在罗格斯大学首席研究员的实验室中进行，而其他更复杂的表征将通过机构间的有效合作进行。这项研究将在学生中进行。他们将获得凝聚态物理和材料科学前沿领域的高级培训，从而为进入科学/技术劳动大军做好准备。

This proposal focuses on the microscopic electronic/magnetic/structural inhomogeneity found in functional oxides, and its corresponding roles in the macroscopic physical response of these materials, such as magnetoresistance, magnetic permeability, piezoelectric constants, and linear and/or non-linear optical characteristics. Understanding and controlling the inter-relationship between the inhomogeneity and physical response are of paramount importance for the development of new advanced electronic and magnetic devices. The concepts of thermodynamic or quantum criticality, soft modes, disorder effects and electronic phase separation will be important to understand the coexistence or fluctuations of neighboring phases in phase space. The activities envisioned in this program include a few important classes of complex oxide materials. The first topic is the area of magnetoresistive materials (such as CuIr2S4-CuCr2S4 and also (Bi,Sr)MnO3-(La,Sr)MnO3), showing a competition between, as well as a coexistence of, charge-ordered-insulating and ferromagnetic-metallic phases. Other topics include the enhanced piezoelectric response near MPB of ferroelectric relaxors (PMN-PT) and chemical pressure effects in geometrically frustrated antiferromagnets such as ZnCr2O4. We will also study tunneling magnetoresistance in polycrystalline films as well as a trilayer structure of double perovskite (Ca,Sr,Ba)Fe0.5Mo0.5O3. The success of this project will critically depend on a comprehensive characterization of the functional, complex oxides (or chalcogenides) as well as the fabrication of high-quality polycrystalline materials and single crystals. Materials synthesis and classical characterization including magneto-transport, susceptibility, and thermodynamic measurements will be done in the PI's lab at Rutgers University. In addition, x-ray scattering, neutron scattering, TEM, microwave, Raman, and low-temperature STM experiments will be performed through inter-institutional collaborations. This research will be conducted with the assistance of students who will thereby be prepared for entry into scientific/technological careers in industry, government or academia. %%%Modern electronic and magnetic devices often utilize physical responses of materials when the materials are exposed under external parameters such as magnetic or electric fields, pressure, or optical irradiation. Recent investigation has suggested that the large-scale physical response such as magnetoresistance, piezoelectricity, or linear and/or non-linear optical response can be drastically enhanced in materials with microscopic electronic/magnetic/structural inhomogeneity. Thus, this enhanced response in microscopically inhomogeneous materials can provide the scientific underpinning for future technologies. In this project we focus on understanding as well as controlling the inter-relationship between the microscopic inhomogeneity and macroscopic physical response. The inhomogeneity can be associated with various charge/spin/orbital degrees of freedom, and may accompany dynamic fluctuations, in addition to static spatial fluctuations. We will primarily investigate functional, complex oxides and also other chalcogenides, showing various competing or mutually antagonistic ground states. The success of this project will critically depend on a comprehensive characterization of the materials as well as the fabrication of high-quality polycrystalline materials and single crystals. Fabrication and basic characterization of the materials will be performed in the laboratory of the Principal Investigator at Rutgers University, while other more complex characterization will be performed through functioning inter-institutional collaborations. This research will be conducted with students. They will acquire advanced training in a forefront area of condensed matter physics and materials science and thus prepare them to enter the scientific/technological workforce.