General Colloquium
April 26 - 4:00pm Phys 223
(Coffee at 3:30p.m. in room 242)
Iowa State University, Ames, Iowa
April 26 - 4:00pm Phys 223
(Coffee at 3:30p.m. in room 242)
Douglas Finnemore
Distinguished Professor in Liberal Arts and Sciences - Chairman
Iowa State University, Ames, Iowa
Title:"Superconductivity at 40 K in MgB2, a Brand New Arena"
Akimitsu's discovery of superconductivity at 40 K in MgB2 is a special event because it is first superconductor with this crystal structure and because the transition temperature is uncommonly high for a p-band metal. The boron atoms are in hexagonal sheets similar to graphite with magnesium atoms above and below the center of each hexagon. The Fermi surface seems to be dominated by contributions from the boron p-bands. Early experiments show that there is a large boron isotope effect indicating that the electron-phonon interaction plays a major role in the superconductivity. The size of the Cooper pairs is about 5 nm; the magnetic field penetration depth is about 130 nm; the energy gap is about 4.5 meV; the upper critical field is about 16 Tesla, the electron-mean-free-path is about 60 nm; in short, it looks like a classical d-band superconductor. From a practical point of view, the primary factor is the ease with which supercurrents are transmitted through grain boundaries in contrast to the behavior of the cuprate superconductors. At first sight, it looks simple and low cost, but you never know until you have done it.