Electronic structures and superconductivity of endohedrally doped C28 solids from first principles

Abstract

We present ab initio calculations of the crystalline phases of C28: hyperdiamond and hyperlonsdaleite, in their pristine and endohedrally doped forms. These are hard materials with strong covalent bonds between the C28 molecules, and yet their electronic properties have remarkable similarities to the weakly bonded C28H4 molecular solids previously investigated [Phys. Rev. B 70, 140504(R) (2004)]. Our calculations show that they exhibit very narrow bands near the Fermi energy with an electron-phonon coupling that is well described by a molecular model and is larger than in C60. Our study focuses on C28 solids endohedrally doped with Zr, a group-IVB tetravalent atom. Solid Zr@C28 is a small-gap insulator with Jahn-Teller distortions. Since the two structures considered are degenerate in energy, the actual material is expected to have disorder affecting the states at the Fermi energy and leading to a nonvanishing density of states. We conclude that the small density of states at the Fermi energy for Zr@C28 will lead to a superconducting transition temperature Tc lower than that found in K3C60; however, our results suggest that a higher Tc may be obtained using group-IIIB trivalent atoms.

Source-reported materials — not catalogue approval

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