Metal-insulator transition in ammoniatedK3C60

Magnetic susceptibility, electron spin resonance, and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ nuclear-magnetic-resonance data on N${\mathrm{H}}_3$ ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ reveal that N${\mathrm{H}}_3$ ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$ is a narrow-band metal with a transition to an insulating ground state at 40 K. This transition suppresses the superconductivity that is expected to occur at around 30 K according to a simple empirical relation between $T_c$ and the cell volume in alkali-metal-doped ${\mathrm{C}}_{60}$ superconductors.