Identifying superconducting materials with strong electron phonon coupling and high critical temperatures under ambient pressure constitutes a frontier in contemporary condensed matter physics. Here, we report a pioneering investigation of the influence of carrier concentration and phonon softening on superconductivity in the doped diamond and cubic boron nitride (c-BN) system. First-principles calculations indicate that the maximum achievable hole concentrations are $5.0\times {10}^{22}$ and $5.3\times {10}^{22}\mathrm{holes}/{\mathrm{cm}}^3$ for the diamond and c-BN structures, which induce superconducting critical temperatures of 136 and 110 K, respectively. At the maximum theoretically achievable hole concentration, the valence band maximum crosses the Fermi level, forming triply degenerate hole pockets near the $\mathrm{\Gamma }$ point. Flat bands emerge near the Fermi level along the high-symmetry L-W path, and a Van Hove singularity appears at the L point, leading to a pronounced density of states peak at the Fermi level. These carrier features promote softening of the $T_{2g}$ phonon mode at the $\mathrm{\Gamma }$ point, resulting in enhanced phonon coupling strength ${\lambda }_{qv}$ and phonon linewidth ${\gamma }_{qv}$, thereby strengthening the overall electron phonon interaction. These findings provide important theoretical insights into the correlation between carrier concentration and superconducting critical temperatures in conventional superconductors.

Close

PrevNext

View figure in article

• Charge
• Electrical properties
• Superconductivity
• 3-dimensional systems
• Clathrates
• Diamond
• BCS theory
• Band structure methods
• Density functional theory
• Free-electron model