16 July 2015 Graphene electrons share the heat

An oscillating electric field with a period on the order of a picosecond leads to an increase of the common temperature of the graphene electrons, which can be described using simple thermodynamics.

Simple thermodynamics describes how fast oscillating electric fields lead to carrier heating in graphene. Graphene - a one-atom-thick sheet of carbon atoms – is known to be a very good electrical conductor. Therefore, a multitude of applications in modern nano-electronics are envisioned, ranging from highly efficient detectors for optical and wireless communications to transistors operating at very high speeds. A constantly increasing demand for telecommunication bandwidth requires even faster operation of electronic devices, pushing their response to shorter time ranges, as short as a picosecond (10-12 s, i.e. one thousandth of a billionth of a second).

A team of researchers from the Max Planck Institute for Polymer Research in collaboration with Klaas-Jan Tielrooij from ICFO, has discovered that electrical conduction in graphene on the picosecond timescale is governed by the same basic laws that describe the thermal properties of gases. For this, they applied to the graphene electrical fields oscillating at terahertz rates, i.e. one thousand billion oscillations per second.

The researchers found that the energy of ultrafast electrical currents passing through graphene is very efficiently converted into electron heat, making graphene electrons behave just like a hot gas: the heat is distributed evenly over all electrons. The rise in electronic temperature, caused by the passing currents, in turn has a strong effect on electrical conduction of graphene. The study entitled “Thermodynamic picture of ultrafast charge transport in graphene”, has recently been published in Nature Communications.

Such a simple thermodynamic approach to the ultrafast electrical conduction in graphene will allow scientists and engineers to better understand and improve the performance of graphene-based nano-electronic devices such as ultra-high-speed transistors and photo-detectors.