Jun Kondo applied third-order perturbation theory to the Kondo model and showed that the resistivity of the model diverges logarithmically as the temperature goes to zero.
[2] This explained why metal samples containing magnetic impurities have a resistance minimum (see Kondo effect).
A number of methods were used to attempt to solve the Kondo problem.
Phillip Anderson devised a perturbative renormalization group method, known as Poor Man's Scaling, which involves perturbatively eliminating excitations to the edges of the noninteracting band.
[3] This method indicated that, as temperature is decreased, the effective coupling between the spin and the band,
The Kondo problem was finally solved when Kenneth Wilson applied the numerical renormalization group to the Kondo model and showed that the resistivity goes to a constant as temperature goes to zero.