Energy Dissipation on Dirac and 2D Material Surfaces

Energy dissipation at material surfaces controls the rate of chemical reactions, the efficiency of novel technology, friction and lubrication, as well as materials growth including nanostructures. The current project seeks to obtain a deeper understanding of how energy dissipates on novel material surfaces, focusing on Dirac and two-dimensional materials. The first Dirac material was graphene, a single layer of carbon atoms followed by the so-called topological insulators and later by an entire class of new two-dimensional materials and even superconductors. The discovery of these materials is so recent that many fundamental questions are still wide open, with a strong potential for the discovery of novel physical and chemical aspects in addition to the materials being promising candidates for future use in technological applications. The first aspect of the project concentrates on how energy dissipates on these novel material surfaces, and the role of the electron-phonon coupling in these complex materials: Electronic transport, i.e. the movement of electrons in a conducting material is coupled to atomic vibrations, so-called phonons. The electron-phonon (e-ph) interaction at surfaces is one of the most important mechanisms for energy dissipation in electronic transport and its understanding is therefore of huge importance for future low-power technologies. It is also at the heart of conventional superconductivity - i.e. in materials where the electrical resistance drops to zero when it is cooled below a certain temperature which corresponds to dissipationless electronic transport. In these superconducting materials, phonons mediate the required attractive interaction between electrons. As a second aspect, the project aims to quantify the role of energy dissipation in the motion and dynamics of molecules at surfaces. Molecular motion is determined by the rate of energy transfer between the molecule and the surface over which it translates. In analogy to macroscopic motion, energy dissipation can be quantified in terms of atomic-scale friction. A central question for this motion is, in what way the molecule dissipates energy to the surface during its motion, which further governs the type of molecular motion and how fast and far the molecule may travel. Following the motion of individual molecules at surfaces is deceptively difficult and direct studies of these elementary events are scarce. Within this project, studies at industrially relevant temperatures will be carried out at the Cambridge atom scattering centre. Finally, by studying example systems from different material families we will learn about general trends i.e. how values such as the e-ph coupling and the atomic-scale friction change and their influence on energy dissipation.