Seminars Archive

Ultra-low temperature ARPES on strontium ruthenates

Abstract
As the early photoemission and scanning tunneling microscopy experiments were confronted with a problem of surface reconstruction, surface ageing was proposed as a solution to access the bulk states. We demonstrate that, in the case of Sr2RuO4, circularly polarized light can be used to distinguish between signals from the bulk and surface layers, thus opening the possibility to investigate many-body interactions both in bulk and surface bands. The proposed procedure enabled us to detect an unexpected splitting of the surface β band and a notable difference in the renormalization of the bulk and surface α band. We argue that Rashba effect at the surface might be responsible for the splitting of the surface β band, while enhanced electron-phonon coupling at the surface may explain stronger renormalization of the surface α band. Further, combining our experimental data with tight-binding (TB) approach, we produce a maximally precise description of low energy band structure of Sr2RuO4. The resulting model can be used to obtain band velocity and orbital character for any arbitrary momentum point. In particular, the density of states, and hence Sommerfeld coefficient γ~40mJ/
molRu
K2, which is in perfect agreement with direct bulk sensitive measurements. The developed model is meant to be used as more realistic input for various calculations aimed at understanding of unconventional superconductivity in Sr2RuO4.