Scanning tunneling spectroscopy of delafossites
Named in honour of the French crystallographer Gabriel Delafosse, the delafossites are layered materials with triangular in-plane lattices. hey can exist in many chemical combinations, and display a wide range of physical properties. Our current research focuses on the metallic delafossite oxides such as PdCoO2, PtCoO2, PdCrO2 and PdRhO2. These show some of the most spectacular properties of any known metals, with extremely high electrical conductivity which can even exceed that of noble metals, and whose origin is not yet very well understood. There is good evidence that this electrical transport may take them into a ‘hydrodynamic’ regime that has been discussed theoretically for over fifty years but not previously observed in a bulk material . Since they are layered compounds, the delafossites are well suited to study with modern surface spectroscopies such as scanning tunneling spectroscopy.
The extremely high conductivity of the delafossite metals indicates that the usual scattering mechanisms, like scattering from defects, electron-phonon and electron-electron interactions are somehow suppressed compared with those expected in standard materials. Modern spectroscopies have the resolution to investigate this issue quantitatively. The goal of this project is to understand the role of defect scattering by performing atomically-resolved imaging and spectroscopy in the vicinity of individual scattering centres. It will also be possible to to search for signatures of electron-phonon interactions. The successful applicant will work with crystals grown and characterized in the group of Andy Mackenzie at MPI Dresden, and spend some time there working on them. Atomic-scale scanning tunneling microscopy and spectroscopy experiments at low temperatures will be performed in the new ultra-low vibration facilities in the group of Peter Wahl at the University of St Andrews. Initially, the study will focus on PdCoO2, for which the electronic structure is already established from quantum oscillations , but the work will be extended to PtCoO2, PdCrO2 and PdRhO2 as appropriate.
The information obtained from these experiments will be complementary to data obtained by angle resolved photoelectron spectroscopy, and if an exceptionally well-qualified applicant were interested in a project combining the two techniques, we would be happy to discuss it.
 P.J.W. Moll, P. Kushwaha, N. Nandi, B. Schmidt, A.P. Mackenzie, Science 351, 1061 (2016)
 C.W. Hicks, A.S. Gibbs, A.P. Mackenzie, H. Takatsu, Y. Maeno and E.A. Yelland, Phys. Rev. Lett. 109, 116401 (2012)