Researchers from the University of Groningen and the University of Manchester have directly detected the Peltier effect in graphene that is either one or two atoms thick. The Peltier effect is an example of Thermoelectrics: the field of study that deals with situations in which a temperature difference creates an electric potential, or vice versa. In this effect, a temperature difference appears when a voltage is applied between two electrodes connected to a semiconductor material. The team unambiguously showed that the effect can be switched from heating to cooling by tuning the type and density of the charge carriers inside the material.

The researchers used graphene because of its 2D nature, and graphene is a wonderful candidate for demonstrating a fully tuneable Peltier effect. The electrical contacts to graphene allowed to electrically control the cooling and heating via the Peltier effect, and to detect this cooling and heating, the researchers constructed sensitive nanoscale thermometers that directly measured the temperature of electrons in graphene. This practical approach is said to be the first of its kind for 2D materials, and its sensitivity is a thousand times better than that of its predecessors, down to 0.1 milliKelvin.

Thermoelectrics can play a significant role in heat managing and in generating electrical energy from wasted heat. The emerging family of 2D materials, like graphene, offers exciting opportunities because it's relatively easy to tune their thermoelectric properties. Therefore, the scientific interest on the interaction between charge and heat in such materials opens the door to both novel fundamental studies, and can help realize more sustainable electronics.