In the history of materials development, many classic materials (Si, III-Vs, organics, etc.) which can be produced reliably at large scale eventually have found critical applications after decades of intensive research, leveraging their distinctive properties. For example, silicon dominates the field-effect-transistor technology because perfect dielectric-silicon interface can be readily realized. Organic materials are currently widely used in flat-panel displays, because of their great light emitting properties and the availability of cost-effective production techniques. In this talk, I will first discuss the unique properties of graphene, the first two-dimensional material isolated about 15 years ago, including ultralow heat capacity, high mobility, and weak electron-phonon coupling strength. Leveraging these unique properties, I will then present an efficient mid-infrared photodetector based on graphene plasmons operational at room temperature. Since high-quality wafer-scale graphene can already be produced routinely, such efficient mid-infrared photodetectors may find applications in high-speed thermal imaging and free-space communications.