It is experimentally well established that the Cr(001) surface exhibits a sharp resonance around the Fermi level. However, there is no consensus about its physical origin. It is proposed to be either due to a single particle $d_{z^2}$ surface state renormalized by electron-phonon coupling or the orbital Kondo effect involving the degenerate $d_{xz}/$ $d_{yz}$ states. In this paper we examine the electron-phonon coupling of the Cr(001) surface by means of ab-initio calculations in the form of density functional perturbation theory. More precisely, the electron-phonon mass-enhancement factor of the surface layer is investigated for the 3d states. For the majority and minority spin $d_{z^2}$ surface states we find values of 0.19 and 0.16. We show that these calculated electron-phonon mass-enhancement factors are not in agreement with the experimental data even if we use realistic values for the temperature range and surface Debye frequency for the fit of the experimental data. More precisely, then experimentally an electron-phonon mass-enhancement factor of $0.70\pm 0.10$ is obtained, which is not in agreement with our calculated values of 0.19 and 0.16. Our findings suggest that the experimentally observed resonance at the Cr(001) surface is not due to electron-phonon effects but due to electron-electron correlation effects.

• Received 9 January 2018
• Revised 26 February 2018

DOI:https://doi.org/10.1103/PhysRevB.97.165438