Study Of New Superconductor MgB₂: Electronic Structures And Impure Effects

Human beings first discovered the phenomenon of superconductivity in 1911.For the pursuit of higher Tc value, people conducted a lot of research work. Until 1986 the discovery of high-temperature superconductors was the most exciting milestone in modern physics during past decades. For 12 years people have been found more than 100 species of non-metallic and copper oxide high-temperature superconducting materials for the foundation, Their physical and chemical nature of these anomalies is far beyond what people had expected. Understand the phenomenon of high-temperature superconductors and the nature of such solid has become an important part of Solid scientific fields. The unusual nature of high-temperature superconductors clearly not limited to its high - Tc value, other anisotropy of the nature and structure due to the strong interaction between electron and spin, electron and electron, electron and lattice. Its superconducting properties closely related to the unusual characteristics of the normal state. January 10, 2001, the professor come from Japan Institute of the University of Castle Peak announced, they found that Magnesium diboride metal compounds with super conductivity, the superconducting transition temperatures as high as 39k .With the development of computer technology, First - principles calculations have become an important tool for molecular research .Our work based on the density functional theory, linear augmented plane-wave method, study the electronic structure of Two superconducting energy gap magnesium diboride .During the calculation of electron-doped and hole doping in MgB₂,we use aluminum atoms to replace Mg atoms, carbon atoms instead of boron atoms .At the Fermi energy Magnesium diboride formed four bands ,two of them areσband, Mainly constituted by p_x+p_y component, the other two areÏ€band, formed mainly by pz orbit.σband play a major role in superconductivity .In MgB₂ superconductors , the Mg atoms can be replaced by aluminum and scandium to form Mg_1-xAl_xB₂ and Mg_1-xSc_xB₂, Boron can be replaced by carbon to form Mg(B_1-yC_y)₂. In such cases the substitute atom contain more than one electron outside the core. For example Al:3s23p1;Sc:4s23d1;C:2s22p2. Experiment shows, whether in which substitute, Magnesium diboride Tc superconducting critical temperature will drop. We found no matter which type of doping critical temperature dropped connected with saturation of the band and interband scattering .The electron outer these substitute atoms occupyσband ,when these bands become saturation, it conducted decline of the superconductivity of the material .In addition, Full-Potential Linearized Augmented Plane Wave plus local orbital method (FPLAPW +lo) calculations were performed for Fe2VAl and Fe3Al in order to investigate magnetic and optical properties and to show the origin of various optical transitions. It was found that the lattice constant and spin magnetic moments with the GGA method differ more from the respective experimental values than those calculated with the LSDA method. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method were in overall better agreement with experiment. Our predictions agreed well with recent experimental reflectivity spectra. Meanwhile, the spectral peaks at the transitions were analyzed from the imaginary part of the dielectric function.