Superconductivity research on boron solids and an efficient doping method

Abstract

Boron solids are, similar to diamond, strong electron-phonon coupling systems and therefore potentially have high-Tc superconductivity. For realizing high transition temperature Tc, however, careful control of the valence electrons is necessary, which requires detailed understanding of the electronic structure. By critically reviewing recent development in this field, along with the situation in heavily doped diamond and clathrates, we show a promising route for high Tc in boron system. Although both α- and β-boron become metallic and exhibit superconductivity at high pressure, the strong covalent character still remains, which significantly limits its Tc achieved by applying high pressure. Heavy doping of related compounds is desirable, as long as the basic electronic structure is retained, but it is extremely difficult at normal conditions. A promising method to achieve this is high pressure synthesis. Similar technique is useful for heavy doping of diamond. To design high-pressure experiment, the role of theory is important through predicting the phase diagram, which was not available for boron previously.