A new class of high Tc superconductors having a dense carbon framework structures is predicted using first-principles calculations.
The current search for high-temperature superconductivity is now focused on materials containing low-Z elements due to the large phonon contribution necessary for BCS-type behavior. An additional strategy for isolating appropriate compositions and pressure conditions is suggested by the prediction that high temperature superconductivity is likely to be found in high-density materials with strong sp3 bonding and high lattice symmetry.
Sodalite carbon frameworks doped with simple metals such as Li, Na, and Al appear to meet this set of criteria very well. Although such materials share some common features with doped diamond, their doping level is not limited and the density of states at the Fermi level can be as high as that in MgB2. Now computational work (Fig. 1) shows that these factors can boost the superconducting temperature (Tc) in these materials to values higher than that of doped diamond.
For example, the superconducting Tc of sodalite-like NaC6 is predicted to be above 100 K. This phase and a series of other sodalite-based superconductors are predicted to be metastable phases but dynamically stable. Owing to the rigid carbon framework of these and related dense carbon materials, doped sodalite-based structures could be recoverable as potentially useful superconductors [Lu et al., Phys. Rev. B 93, 104509 (2016)].