Experimental Observation and Theoretical Description of the Pure Fano Effect in the Valence-Band Photoemission of Ferromagnets

The pure Fano effect in angle-integrated valence-band photoemission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photoelectrons has been avoided by an appropriate choice of the experimental parameters. The theoretical description of the resulting spectra reveals a complete analogy to the Fano effect observed before for paramagnetic transition metals. While the theoretical photocurrent and spin-difference spectra are found in good quantitative agreement with experiment in the case of Fe and Co, only a qualitative agreement could be achieved in the case of Ni by calculations on the basis of plain local spin-density approximation. Agreement with experimental data could be improved in this case in a very substantial way by a treatment of correlation effects on the basis of dynamical mean field theory.

Figure 1

Left: spin and angle-integrated VB-XPS spectrum of ferromagnetic Fe, Co, and Ni for a photon energy of 600 eV. Right: spin difference $\Delta I^{+}=I_{\uparrow }^{+}-I_{\downarrow }^{+}$ of the photocurrent for excitation with left circularly polarized radiation. Theory: solid line; experiment: dashed line. The same scale has been used for the intensity and corresponding spin-difference plots.

Figure 2

The spin-resolved self-energies of ferromagnetic Ni calculated within the DMFT for $U=3\mathrm{eV}$, $J=0.9\mathrm{eV}$, and $T=500\mathrm{K}$. The real parts (solid lines) and imaginary parts (dashed lines) are shown separately for the $t_{2_g}$ (thick lines) and $e_g$ (thin lines) representations of the $d$ states.

Figure 3

Left: The experimental (dashed lines), theoretical LSDA (dot dashed lines) and $\mathrm{LSDA}+\mathrm{DMFT}$ (solid line) data for spin and angle-integrated VB-XPS spectra of Ni for a photon energy of 600 eV. Right: spin difference $\Delta I^{+}=I_{\uparrow }^{+}-I_{\downarrow }^{+}$ of the photocurrent for excitation with left circularly polarized radiation.