We report the observation of a magnetic contrast of up to 20% in the scanning tunneling spectroscopy dI/dV maps obtained with Fe-coated tips on Mn(001) layers grown on an Fe(001) whisker at 370 K. These nanometer resolution microscopy results show that the layers couple antiferromagnetically. By normalizing the dI/dV curves by tunneling probability functions, we found a spin-dependent peak on the body-centered-tetragonal (bct) Mn(001) surface at +0.8 V, whose high spin polarization gives rise to the dI/dV map contrast. Band structure calculations allow one to identify the +0.8 V peak as due to two spin-polarized d(z(2)) surface states.
Low-temperature scanning tunneling microscopy and spectroscopy investigations of the atomically clean Cr(001) surface together with density functional and many-body calculations have been used to study the surface electronic structure. The Friedel oscillations near impurity atoms have been observed and explained within the Fermi surface analysis. A very narrow resonance at 26 meV above the Fermi level has been observed and the orbital character of corresponding state has been visualized. The experimental data together with many-body calculations give further evidence that the observed resonance is an orbital Kondo resonance formed by two degenerated dxz, dyz surface states. This gives evidence of strong correlation effects on transition metal surfaces.
A CT A P HY SIC A P O LO N IC A A No . 3{ 4 P r oceedi ng s o f t h e 3rd I n t ern at io n al Sy m p osi u m on Scan ni n g Pr o b e Sp ect rosc opy , SPS '0 3
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