Pogrebnyakov et al., PRL 93, 147006 (2004)

1. Hybrid Physical-Chemical Vapor Deposition of MgB2 Thin FilmsXiaoxing Xi and Joan Redwing, Penn State UniversityDMR-0306746 Since the discovery of superconductivity in MgB2 near 40 K, many techniques have been used to further increase Tc without success. In our epitaxial MgB2 thin films grown by HPCVD, we have achieved Tc as high as 41.8 K, higher than in MgB2 produced by any other technique. This is due to biaxial tensile strain in the films caused by the coalescence of initially nucleated discrete islands. First-principles calculations and Raman scattering measurement both revealed that the underlying mechanism for the Tc increase is the softening of the bond-stretching E2g phonon mode. (SEM image of an MgB2 film at the initial growth stage, showing nano-scale growth islands . These islands would coalesce when the film is thicker, generating coalesce tensile strain.) Pogrebnyakov et al., PRL 93, 147006 (2004)

2. Hybrid Physical-Chemical Vapor Deposition of MgB2 Thin FilmsXiaoxing Xi and Joan Redwing, Penn State UniversityDMR-0306746 Education: Three undergraduates (David M. Lishego, Eric Maertz, and William Edson) and two graduate students (Yi Cui and Daniel Lamborn) contributed to this work. The undergraduate students were supported by NSF through the REU program. Societal Impact: Our work may lead to MgB2 magnets for applications in MRI operating at over 20K, replacing liquid helium cooling by efficient cryocoolers. Such MRI systems will be lighter, of lower operation cost, more reliable, and more accessible to populations in remote locations or in developing countries. The PI looked on as high school students from Philadelphia were engaged in hand-on activities on superconducting levitation. It was part of the “Windows on The Microscopic World of Materials” on October 29, 2004, at Penn State University.