Resonant exchange interaction in semiconductors

We present a nonperturbative calculation of indirect exchange interaction between two paramagnetic impurities via two-dimensional (2D) free carriers gas separated by a tunnel barrier. The method takes into account the impurity attractive potential which can form a bound state. The calculations show that if the bound impurity state energy lies within the energy range occupied by the free 2D carriers the indirect exchange interaction is strongly enhanced due to resonant tunneling and exceeds by a few orders of magnitude what one would expect from the conventional Ruderman-Kittel-Kasuya-Yosida approach.