Theoretical investigation of superconductivity in diamond: Effects of doping and pressure

The electronic structure, lattice dynamics, and electron–phonon coupling of pure, boron and nitrogen-doped diamond carbon were investigated using first-principle calculations within the generalized-gradient and virtual crystal approximations. To examine the influence of the impurity content and pressure on the superconductivity of these systems, the electron–phonon coupling constant (λ) and the critical temperature (Tc) were calculated as a function of concentrations from 0 to 15% and pressures from 0 to 90 GPa. Regarding the boron-doped diamond, calculations indicated that its electron–phonon coupling strongly relates to the optical phonon modes, and the estimated critical temperatures matched previous theoretical and experimental results. Regarding the nitrogen-doped case, it was observed that both λ and Tc were larger than those obtained for the hole-doped case. The most distinguishing feature of this system was its rising acoustic contribution to the electron–phonon coupling, which led to significant values for λ and Tc. The majority of the scenarios investigated here presented a decreasing critical temperature with increasing pressure. In contrast to the other cases, C0.85N0.15 exhibited a positive dependence between Tc and pressure leading to a superconducting transition temperature of about 122 K at 20 GPa.