Giant nonlinear absorption by an ensemble of metallic grains

We have investigated the nonlinear low-frequency microwave absorption of an ensemble of small metallic grains. Earlier Zhou et al. [Phys. Rev. Lett. 7 7, 1958 (1996)] have proved that linear absorption by such a system us due to a mesoscopic relaxation mechanism, for which important contribution is f rom the grains with small level spacings between the ground state and the f irst excited state. Here we have shown further that such grains are anomalo usly sensitive to the field amplitude and the distribution of level spacing s. Since such a behavior depends on external magnetic field we expect the a ppearance of a giant nonlinear magnetoresistance, as well as a very strong temperature dependence of the non-linear microwave conductivity.