Anisotropic mass renormalization in Sr2RuO4

The layered perovskite Sr$_{2}$RuO$_{4}$ continues to attract interest as a model system of a multiband Fermi liquid. Previous dHvA and ARPES studies successfully determined its Fermi surface [1, 2] and reported a large and sheet dependent renormalization of the Fermi velocity due to electron-electron interactions with v$_{band}$/v$_{F}$ ranging from $\approx$ 3 for the d$_{xz/yz}$ derived $\alpha$ and $\beta$ sheets to $\approx$ 5.5 for the $\gamma$ sheet with dominant dxy orbital character [1, 3]. Here, we report new high-resolution ARPES data revealing an additional strong momentum dependence of the renormalization within a single Fermi surface sheet. This effect is most pronounced in the $\gamma$ band and is larger than expected from the mixing of the orbital composition along individual Fermi surface sheets induced by spin-orbit coupling [4,5]. Our observations therefore provide evidence for a genuinely momentum dependent self-energy in the vicinity of a van Hove singularity. \\[0pt] [1] C. Bergemann et al., Advances in Physics 52, 639 (2003) \\[0pt] [2] A. Damascelli et al., Physical Review Letters 85, 5194 (2000). \\[0pt] [3] K.M. Shen et al., Physical Review Letters 99, 187001 (2007). \\[0pt] [4] M.W. Haverkort et al., Phys Rev Lett. 101, 026406 (2008) \\[0pt] [5] J. Mravlje et al., arXiv:1010.5910v1(2010)