DYNAMICS OF IMPURITY SPIN ABOVE KONDO TEMPERATURE .I. CALCULATION OF SPIN PROPAGATOR AND STATIC SUSCEPTIBILITY

The dynamics of impurity spin contained by nonmagnetic host metal is investigated theoretically. The pseudofermion representation proposed by Abrikosov is applied to impurity spin. The calculations are carried out keeping only the leading logarithmic terms in any order of the perturbation theory. This approximation is adequate only above the Kondo temperature. Abrikosov's method is slightly modified to treat the spin dynamics. The real and the imaginary part of the pseudofermion self-energy is calculated. The imaginary part of the self-energy satisfies a simple relation which holds between the electron and pseudofermion self-energies. The decrease in the effective gyromagnetic factor is determined, which shows how the spin compensated state begins to form at low temperature. The first terms of the power series of the static susceptibility calculated from the pseudofermion Green function are in agreement with the results of the previous perturbative calculations given by e.g. Yosida and Okiji. The spectral function of the pseudofermion propagator is discussed in details. It has a long tail at large positive energies and satisfies the sum rule {Mathematical expression}. The dynamic susceptibility and other physical quantities will be presented in the second part of this paper. © 1969 Springer-Verlag.