Tunneling Spectroscopy of bcc (001) Surface States

We have discovered an intense, sharp feature in tunneling spectra of the Fe(001) and Cr(001) surfaces that derives from a bcc surface state near the Fermi level. Band-structure calculations show that this state is a general feature of bcc (001) surfaces, and that it originates from a nearly unperturbed $d$ orbital extending out into the vacuum region. This general feature should permit chemical identification with atomic spatial resolution on bcc (001) surfaces. The surface state is in the minority spin band for Fe and Cr, so it should be useful for future spin-polarized tunneling experiments.