  Over the past 20 years, fullerides have been studied as the source of
high-transition-temperature (Tc) superconductivity except for copper oxides.
The recent finding of the Mott insulating state right beside superconductivity
in Cs3C60 has suggested that magnetism helps raise Tc even in fullerides as in
heavy-fermion compounds, high-Tc copper oxides, two-dimensional organic
conductors, and iron pnictides. Namely, one tends to think that the link
between Mott insulator and superconductivity takes place in fullerides, which
can give rise to the mechanism beyond the Bardeen-Cooper-Schrieffer framework.
However, the relationship between the Mott state and the superconductivity in
Cs3C60 is still under debate. By nuclear magnetic resonance measurements under
pressure, we find that the magnetism and superconductivity in Cs3C60 are
competing orders. Different from previous reports, the phase separation of
Cs3C60 crystals into the Mott and metallic states allows us to systematically
study the evolution of the ground state under pressure. Our careful experiments
have found that the prevention of a magnetic order is rather essential for the
superconductivity in face-centred cubic Cs3C60, which presents a basic strategy
for finding still higher Tc in this system.
