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

最近发现的二硼化镁（MgB2）的超导性不仅表现出在常规超导体中最高的39 K超导转变温度，而且具有区别于传统BCS超导体的独特的多带行为。带内和带间耦合和散射之间的相互作用导致了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，该技术已经生产出迄今为止报道的最干净的MgB2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。该个人研究者奖支持研究具有不同程度耦合和散射率的MgB2基薄膜的各种超导和正常状态传输特性。通过集体测量，该项目最终可以揭示当带内和带间散射率系统变化时，两个带的存在如何改变超导和正常状态行为在不同温度，电流和磁场下。该项目将对理解多波段对物理性质的影响，特别是对超导性质的影响产生重大影响。它还可能导致通往大临界场和临界电流的优化路径，这对高场磁体和电力的潜在应用具有重要意义。该项目为研究生和本科生提供了广泛的教育和培训机会，特别是为来自没有大量研究基础设施的大学的本科生和高中科学教师提供了暑期研究项目。最近，一种新的超导体——二硼化镁（MgB2）被发现，它在金属中具有最高的超导转变温度（材料电阻变为零的温度），为39k。材料中的电子组成带。在大多数导体和超导体中，只有一个能带的电子对材料的导电和超导特性起作用。然而，MgB2具有独特的电子带结构，其中来自多个带的电子有助于这些性质。电子在带内和带间散射的相互作用导致了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已经开发出一种技术，可以生产出迄今为止报道的最干净的MgB2薄膜。该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MgB2基薄膜的各种超导和正常状态特性的研究。通过各种测量，该项目最终可以揭示两个能带的存在如何改变超导和正常状态行为。该研究还可能导致找到一种优化的途径，以获得在大磁场中保持超导性并能够承载大电流的材料，这对于在高场磁体和电力领域的潜在应用具有重要意义。该项目为研究生和本科生提供了广泛的教育和培训机会，特别是为来自没有大量研究基础设施的大学的本科生和高中科学教师提供了暑期研究项目。

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.