portrait portrait

The 15th International Conference on

Vibrations at Surfaces

June 22-26, 2015 ▪ Donostia-San Sebastián, Spain

Donostia Igeldotik

Invited talk

Electron phonon mediated transitions in 2D materials; towards a designer superconductor?

J. W. Wells

Norwegian University of Science and Technology (NTNU), Trondheim, Norway

Electron-phonon coupling in conductors is largely responsible for electrical resistance, and is a major cause of power dissipation. On the other hand, exceptionally strong electron-phonon coupling is a prerequisite for traditional superconductivity. Thus, adequate control of the electron-phonon interaction could facilitate the conversion of lossy conductors into lossless superconductors.

To be more specific, strong changes in the electron-phonon interaction can be created by a sudden change in the electron density of states (eDOS). Traditionally, this involves the sudden change in eDOS which is found at the Fermi level - but we have demonstrated that other eDOS changes also cause a strong modification of the electron-phonon interaction. This is especially clear in graphene-like materials, where the eDOS change at the sigma band maximum is very much stronger that that at the Fermi level. Through calculational support, we believe that sufficiently strong doping could allow such materials to support a sigma-band superconducting phase to exist.

Additionally, whilst electron scattering between orthogonal bands is forbidden, we have shown that such scattering exists in graphene-like materials when mediated by a phonon interaction (which temporarily breaks the orthogonality). The temporary lattice distortion facilitates scattering between sigma and pi bands in graphene, and also contributes to a total increase in the electron-phonon interaction. With sufficient doping, this interaction would contribute to an unusually high superconducting transition temperature.

Here, I will present our recent experimental work, alongside simulations and recent calculations. I will show that exceptionally strong electron-phonon coupling exists in the sigma-band of graphene, and that phonon mediation transitions between the pi and sigma bands are also observable. Finally, I will speculate on the possible existence of a superconducting phase in 2D graphene-like materials, and describe our ongoing efforts to realise this experimentally.