Electronic structures of potassium-doped C$_{60}$ encapsulated in BN nanotubes

Boron-nitride nanotubes have large band gap independent of chirality and are promising candidates for nanostructure control. Here, we investigate the electronic structure of potassium-doped C$_{60}$ encapsulated in boron-nitride nanotubes using first-principles methods based on the density functional theory. We demonstrate that the material is one-dimensional metal where conducting electrons are only in the C$_{60}$ chain. Interestingly, the material can have a large Fermi-level density of states, which indicates the possibility of various phase transitions including superconductivity as in the case of fcc K$_3$C$_{60}$. We therefore discuss the electron-phonon couplings as well as the pressure dependence of the electronic structures of this material.