Graphene is a novel two dimensional material with extraordinary electrical and mechanical properties. It also has promising optical and optoelectronic properties: their low energy transitions can be continuously tuned by a gate voltage and fundamentally different behaviors are expected for single- and double- layered graphene. We developed sensitive infrared spectroscopy using a microscopy setup with a femtosecond tunable light source to probe these effects.
In Fig. 1 we show such unusual gate tunable optical transitions in graphene. Fig. 1a is the gated graphene device and Fig. 1b is the change of optical reflection from graphene as a function of electrical gating. The gate-tunable optical transition opens a new dimension in graphene spectroscopy and allows for an optical determination of the graphene electronic structure (Fig. 2).