Temperature-dependent scanning tunneling spectroscopy of Cr(001): Orbital Kondo resonance versus surface state

Abstract

The temperature-dependent surface electronic structure of Cr(001) is investigated by means of scanning tunneling spectroscopy (STS) in the temperature range between 22 and $350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Consistent with earlier observations, a sharp peak is found in the tunneling spectra close to the Fermi level ${E}_{\mathrm{F}}$. While the binding energy remains unchanged, the peak broadens with increasing temperature. The experimental data are fitted within the framework of two physical models, i.e., in terms of a single-particle band theory and an orbital Kondo effect. Both models lead to a reasonable agreement between the fit and the experimental data. Using the Kondo model, a Kondo temperature ${T}_{\mathrm{K}}$ of $123\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is obtained. If interpreted in terms of a single-particle band theory, the fit results in an electron-phonon mass-enhancement factor $\ensuremath{\lambda}$, which is 5--10 times larger than the Cr bulk value.