Low-Energy Electron-Mode Couplings In The Surface Bands Of Sr2ruo4 Revealed By Laser-Based Angle-Resolved Photoemission Spectroscopy

We use angle-resolved photoemission spectroscopy with a 7-eV laser, which is capable of ultrahigh energy and momentum resolutions, and investigate bosonic mode couplings in the surface bands of Sr2RuO4. Significantly, our measurements reveal pronounced kink structures at very low binding energies (similar to 8 and similar to 15 meV), which have a strong variation in the renormalization strength among multiple bands derived from the Ru 4d orbitals. Neutron scattering has observed phonon modes with the lowest energy scale around 15 meV, which thus could be the main source for the similar to 15-meV kink In contrast, the significant coupling at the lower energy (similar to 8 meV) is attributed to magnetic excitations, which are reported to be peaked in density of states around 10 meV. The similar to 8-meV kink is found to be strongest in the two-dimensional 4d(xy)-derived band, implying its mechanism to be the electron coupling to ferromagnetic spin fluctuations.