Electronic structure of the superconducting oxide spinel LiTi2O4

We examine the electronic band structure of Li${\mathrm{Ti}}_2$ ${\mathrm{O}}_4$ in the cubic spinel structure by performing a local-density calculation using the linear muffin-tin orbitals method. The Fermi energy lies in the Ti $3d$ bands with only one-half of an electron per Ti atom occupying this band. The next-lower O $2p$ bands occur about 2.4 eV below the Ti $3d$ bands in good agreement with the photo-electron spectra. However, enhanced specific heat and differences with photoemission spectra near $E_f$ suggest effects beyond the band results. If the specific-heat enhancement is assumed to arise from phonons, we find $\lambda \sim 1.8$ indicating a strong electron-phonon coupling. The nature of electron states is also consistent with the possibility of resonating-valence-bond superconductivity.