High-resolution angle-resolved-photoemission studies of theM¯-point surface state on Cu (001)

High-resolution angle-resolved-photoemission studies were carried out on the surface state reported by Heimann et al. at the $\overline{M}$ point of the two-dimensional surface Brillouin zone of Cu (001). The symmetry of the state is shown to be odd with respect to the (100) mirror plane, as hypothesized by Heimann et al. Experimental $E\left({\overrightarrow{k}}_{\parallel }\right)$ dispersion relations in good agreement with the earlier study are reported, and accurate determinations of peak width as a function of $k_{\parallel }$ are shown to be reasonably well fitted by a simple model. A novel temperature effect is reported and interpreted in terms of substantially enhanced vibrational amplitude of the surface layer.