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

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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.