Kondo effect versus indirect exchange in the two-impurity Anderson model: A Monte Carlo study

The magnetic properties of two Anderson impurities in an electron gas are studied by use of a numerical simulation technique. It is found that magnetic correlations between impurities build up as the temperature is lowered up to roughly the Kondo temperature (${T}_{K}$) and stay constant below ${T}_{K}$. The magnetic susceptibility is quenched on a temperature scale that depends sensitively on the relative size of ${T}_{K}$ and the indirect exchange interaction. When the indirect exchange interaction is much smaller than the Kondo temperature all thermodynamic properties at low temperatures are indistinguishable from the ones obtained for a single-impurity model. The relation of these findings to other work on this problem is discussed.