Zirconium Dodecaboride as the First Superconductor with the Improved Near-Surface Characteristics

Abstract

An overview of experimental results and theoretical calculations for zirconium dodecaboride single-crystal electronic characteristics is given. As shown, the ZrB12 belongs to a class of partially covalent compounds of transition metals with light elements where the presence of boron directional covalent bonds is responsible for high mechanical hardness whereas metallic, and, hence, superconducting properties are formed by d-states of zirconium hybridized with 2p-orbitals of boron. Analysis of experimental data obtained for ZrB12 and YB6 in different laboratories and with different techniques shows that, in contrast to yttrium hexaboride, zirconium dodecaboride is the first known superconductor with an enhanced near-surface order parameter. Qualitative explanation of the effect is presented and based on the Phillips theory of percolative superconductivity.

Keywords