Theory of relativistic photoemission for correlated magnetic alloys: $\text{LSDA}+\text{DMFT}$ study of the electronic structure of ${\text{Ni}}_x{\text{Pd}}_{1-x}$

Electronic correlations play an important role in determining the properties of solid state systems, in particular, in the presence of narrow bands. In intermetallic alloys the strength of correlation effects and, thus, the details of the electronic structure depend on the concentration of the constituents, their interactions, and the degree of chemical order. Although the electronic structure of such a system can be conveniently studied by photoelectron spectroscopy, the interpretation of the spectra is nontrivial. To enable a quantitative analysis of chemically disordered systems showing correlation effects in photoemission spectroscopy we therefore incorporate dynamical mean-field theory in the fully relativistic version of layer-Korringa-Kohn-Rostoker theory and treat the results within the relativistic one-step model of photoemission generalized to the magnetic alloy case. Our ansatz allows the study of complex layered structures like thin films and multilayers and an almost naturally incorporation of a realistic surface barrier potential. We apply our theory to photoemission data of the magnetic alloy system ${\text{Ni}}_x{\text{Pd}}_{1-x}\left(001\right)$ and demonstrating that state-of-the-art photoemission theory is required to deal with this complex system. The comparison over a large alloy concentration range provides us with a means to disentangle the influence of alloying and correlation effects.

Figure 1

(Color online) Spin (left panel) and orbital (right panel) magnetic moments of ${\text{Ni}}_x{\text{Pd}}_{1-x}$ as a function of the concentration $x$ calculated within LSDA and $\text{LSDA}+\text{DMFT}$, respectively. (DMFT parameters: $U_{\text{Ni}}=2.3\text{eV}$, $U_{\text{Pd}}=0.5\text{eV}$, and $J_{\text{Ni},\text{Pd}}=0.9\text{eV}$)

Figure 2

(Color online) Spin- and element-resolved ${\text{Ni}}_x{\text{Pd}}_{1-x}$ DOS’s as a function of the concentration $x$ calculated within $\text{LSDA}+\text{DMFT}$. Upper panel left side shows the paramagnetic Pd DOS. Lower panel right side shows the ferromagnetic Ni DOS. (DMFT parameters: $U_{\text{Ni}}=2.3\text{eV}$, $U_{\text{Pd}}=0.5\text{eV}$, and $J_{\text{Ni},\text{Pd}}=0.9\text{eV}$)

Figure 3

Spin-polarized ${\text{Ni}}_x{\text{Pd}}_{1-x}$ bare Bloch spectral functions for different concentrations $x$. We show the LSDA (first and third row) and $\text{LSDA}+\text{DMFT}$ (second and fourth row) based calculations starting from pure Pd (upper panel, left side) to pure Ni (lower panel, right side)

Figure 4

ARUPS spectra of the ${\text{Ni}}_{0.30}{\text{Pd}}_{0.70}\left(001\right)$ alloy surface for different photon energies in the range from $h\nu =18\text{eV}$ to $h\nu =40\text{eV}$ along $\Gamma \text{X}$ in normal emission. The left panel presents calculated photoemission spectra based on a LSDA electronic structure calculation. The experimental spectra are presented in the middle panel and the theoretical $\text{LSDA}+\text{DMFT}$ based spectra are shown in the right panel. Due to the high concentration of Pd the spectral distribution is more pronounced for higher binding energies.

Figure 5

Same as Fig. 4 but spectra measured and calculated for the ${\text{Ni}}_{0.50}{\text{Pd}}_{0.50}$ alloy system. As expected, Ni- and Pd-generated peak structures are visible with an intermediate energy range between 2 and 4 eV binding energy.

Figure 6

Same as Fig. 4 but spectra measured and calculated for the ${\text{Ni}}_{0.70}{\text{Pd}}_{0.30}$ alloy system. Due to the high concentration of Ni the spectral distributions show the highest intensities for energies near Fermi level.

Figure 7

ARUPS spectra taken from the ${\text{Ni}}_x{\text{Pd}}_{1-x}\left(001\right)$ alloy surfaces as a function of the concentration x for a fixed photon energy of $h\nu =40.0\text{eV}$ along $\Gamma \text{X}$ in normal emission. Experimental data shown at the top panel calculated spectra presented below. Depending on the concentration $x$ a pronounced shift in spectral weight toward the Fermi level is visible.