VIRTUAL BOUND-STATES IN DILUTE NOBLE-METAL BASED DISORDERED ALLOYS ACCORDING TO THE RESONANT MODEL POTENTIAL THEORY

The virtual bound state (VBS) d density of states arising from small concentration of a transitional impurity in noble metals based disordered alloys is calculated from the resonant model potential theory. A simple formula is derived for the impurity density of states. The effect of the noble metal d bands is taken into account by a perturbative method valid for energies outside the host metal d band. The VBS parameters are expressed in terms of the resonant potential parameters and of the number of resonant d electrons Zd (which controls the VBS position with respect to the Fermi level and is assumed to be a constant for each impurity). The theory is applied to NiCu, NiAg, NiAu, TiAu, PdAg and PdAu. The resonant potential parameters are determined from the corresponding perfect metal bandstructures and Zd determined from the observed gold-based alloys resonance position.