Study of Multiband Effects in MgB2 by Controlling Intraband and Interband Scattering in Epitaxial Films

最近发现的镁-二硼化物(MgB_2)超导体不仅具有常规超导体中最高的超导转变温度39K，而且具有区别于传统BCS超导体的独特的多带行为。带内和带间耦合与散射之间的相互作用已被提出，以导致许多丰富和不寻常的性质。宾夕法尼亚州立大学的一个合作小组开发了一种混合物理-化学气相沉积(HPCVD)技术，该技术已生产出迄今报道的最清洁的MgB_2薄膜。它还提供了系统地改变样品中的带内和带间散射的可能性。这一个人研究人员奖支持对具有不同程度耦合和散射率的硼化镁薄膜的各种超导和正常态输运特性的研究。通过集体测量，该项目最终可以揭示当带内和带间的散射率系统地变化时，两个带的存在如何改变不同温度、电流和磁场中的超导和正常态行为。该项目将对理解多带对物理性质的影响，特别是对超导性质的影响产生重大影响。这也可能导致一条通向大临界场和临界电流的优化路径，这对于在高场磁体和电力领域的潜在应用具有非常重要的意义。该项目为研究生和本科生提供了广泛的教育和培训机会，特别是没有实质性研究基础设施的大学本科生和高中科学教师通过暑期研究项目。最近发现了一种新的超导体--二硼化镁(MgB2)，它是金属中超导转变温度(材料的电阻变为零的温度)最高的，为39K。物质中的电子将自己分组成带。在大多数导体和超导体中，只有一个能带中的电子对材料的导电和超导性质有贡献。然而，MgB2具有独特的电子能带结构，其中来自多个能带的电子对这些性质有贡献。电子散射在带内和带间的相互作用已被提出导致许多丰富和不同寻常的性质。宾夕法尼亚州立大学的一个合作小组已经开发出一种技术，该技术已经生产出了迄今为止报道的最干净的MgB2薄膜。这项技术还提供了系统地改变样品中带内和带间电子相互作用的可能性。该奖项支持对不同的硼化镁薄膜的各种超导和正常态特性的研究。通过各种测量，该项目最终可以揭示两个带的存在如何改变超导和正常态行为。这项研究还可能找到一种优化的途径，以获得在大磁场中保持超导并能够携带大电流的材料，这对于在高场磁体和电力领域的潜在应用具有非常重要的意义。该项目为研究生和本科生提供了广泛的教育和培训机会，特别是没有实质性研究基础设施的大学本科生和高中科学教师通过暑期研究项目。

The recently discovered superconductivity in magnesium-diboride (MgB2) not only shows the highest superconducting transition temperature of 39 K among the conventional superconductors, but also unique multiband behaviors which distinguish it from conventional BCS superconductors. The interplay between intra- and inter-band coupling and scattering has been proposed to result in many rich and unusual properties. A collaborative group at Penn State has developed a Hybrid Physical-Chemical Vapor Deposition (HPCVD) technique that has produced the cleanest MgB2 thin films reported so far. It also provides a possibility to systematically change intra and interband scattering in the samples. This individual investigator award supports studies of a variety of superconducting and normal state transport properties of MgB2 based thin films with various degrees of coupling and scattering rates. Through collective measurements, the project can ultimately reveal how the presence of two bands changes the superconducting and normal state behaviors in different temperatures, currents, and magnetic fields when the intra and interband scattering rates are systematically varied. This project will have significant impact on understanding the effect of multi-band on physical properties, especially on superconducting properties. It may also lead to an optimized path to large critical field and critical current, which are very significant for potential applications in high field magnet and electric power. The project provides a broad education and training opportunities for graduate students and undergraduate students, especially for undergraduate students from colleges without substantial research infrastructures and high school science teachers through summer research programs. Recently, a new superconductor, magnesium-diboride (MgB2), has been discovered which has the highest superconducting transition temperature (the temperature where the electrical resistance of a material becomes zero) of 39 K among metals. Electrons in a material group themselves into bands. In most conductors and superconductors only the electrons in one band contribute to the conducting and superconducting properties of the material. However, MgB2 has a unique electron band structure in which electrons from multiple bands contribute to these properties. The interplay of electrons scattering within and between bands has been proposed to result in many rich and unusual properties. A collaborative group at Penn State has developed a technique that has produced the cleanest MgB2 thin films reported so far. This technique also provides the possibility of systematically changing the interactions of electrons within and between the bands in the samples. This award supports studies of a variety of superconducting and normal state properties of different MgB2 based thin films. Through various measurements, the project can ultimately reveal how the presence of two bands changes the superconducting and normal state behaviors. The research may also lead to finding an optimized path to obtain materials that remain superconducting in large magnetic fields and capable of carrying a large current, which are very significant for potential applications in high field magnet and electric power. The project provides a broad education and training opportunities for graduate students and undergraduate students, especially for undergraduate students from colleges without substantial research infrastructures and high school science teachers through summer research programs.