Speaker: Professor Xiaoxing Xi (Temple Univ)

Host: Chunhui Chen

Abstract: Magnesium diboride, a compound known since the 1950s, was discovered to be a superconductor with a transition temperature of 39 K in 2001. The surprise discovery created an explosion of excitement in the superconductivity field, resulting in a relatively quick understanding of its basic properties. Magnesium diboride is a conventional BCS superconductor with a twist – while the Cooper pairs are formed via electron-phonon interactions, its electronic structure has two weekly coupled bands with different symmetries, leading to two separate energy gaps. The two-band nature has led to interesting physics such as the Leggett mode. MgB₂ has also found a broad range of applications in high-field conductors, superconducting electronics, and superconducting radio frequency cavities. Two decades after the discovery of its superconductivity, magnesium diboride continues to appear in conversation on contemporary physics topics, for example the topological superconductor and hydrogen-induced high temperature superconductivity. The materials science and applications of MgB₂ also continue to make significant progresses. As an example, I will present our recent results on ultrathin MgB₂ films. Growing on carbon terminated SiC substrate surface, a MgB₂ film of nominally 2 nm in thickness shows a T_c of 27.2 K and a self-field critical current density J_c(3K,0T) of 2 ×10⁷ A/cm², desirable properties for various superconducting device applications.