Covalent superconductor

The first such material was boron-doped synthetic diamond grown by the high-pressure high-temperature (HPHT) method.

[1] The discovery had no practical importance, but surprised most scientists as superconductivity had not been observed in covalent semiconductors, including diamond and silicon.

The priority of many discoveries in science is vigorously disputed (see, e.g., Nobel Prize controversies).

Similar to diamond, Si:B is type-II superconductor, but it has much smaller values of Tc = 0.4 K and Bc = 0.4 T. Superconductivity in Si:B was achieved by heavy doping (above 8 at.%), realized through a special non-equilibrium technique of gas immersion laser doping.

[20] Both the cubic (3C-SiC) and hexagonal (6H-SiC) phases are superconducting and show a very similar Tc of 1.5 K. A crucial difference is however observed for the magnetic field behavior between aluminum and boron doping: SiC:Al is type-II, same as Si:B.

By substituting a small part of sulfur with phosphorus and using even higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C (273 K) and achieve room-temperature superconductivity.

Parts of a high pressure cell after the synthesis of heavily boron doped superconducting diamond. The diamond (black ball) is located between two graphite heaters
Magnetic AC susceptibility measured as a function of temperature in diamonds enriched with 12 C, 13 C, 10 B or 11 B isotopes. The observation and magnitude of the 12 C- 13 C shift confirms the BCS mechanism of superconductivity in bulk polycrystalline boron-doped diamond.
Structure of CaC 6