Graphene is a single layer of carbon atoms arranged into a honeycomb structure. Since the isolation of graphene in 2004, it has attracted much interest from fundamental and practical viewpoints. Graphene is an ideal two-dimensional system exhibiting quantum Hall effect, and has a linear band dispersion realizing massless fermion described by relativistic quantum physics. Furthermore, graphene may be a promising material for future electronics because of its high mobility, chemical stability, flexibility, high-current capacity, transparency, and low cost.

We have studied the electrostatic carrier control in graphene by use of ionic liquid gate. The electric double layer less than 1 nm formed at the interface between an ionic liquid and graphene may enable extremely high carrier density in graphene. Highly doped graphene is expected to indicate novel exotic phenomena such as conventional/chiral superconductivity, ferromagnetism, and spin/charge density wave.