Two classes of superconductors discovered in our material research: Iron-based high temperature superconductor and electride superconductor

Abstract

We discovered two new classes of superconductors in the course of material exploration for electronic-active oxides. One is 12CaO · 7Al 2O 3 crystal in which electrons accomodate in the crystallographic sub-nanometer-sized cavities. This material exhibiting metal–superconductor transition at 0.2 K is the first electride superconductor. The other is iron oxypnicitides with a layered structure. This superconductor is rather different from high T c cuprates in several respects. The high T c is emerged by doping carriers to the metallic parent phases which undergo crystallographic transition (tetra to ortho) and Pauli para to antiferromagnetic transition at ∼150 K. The T c is robust to impurity doping to the Fe sites or is induced by partial substitution of the Fe 2+ sites with Co 2+ or Ni 2+. This article gives a brief summary of these discoveries and recent advances.