Dipolar broadening of nuclear spin resonance under dynamical pumping

摘要

We study the polarization dependence of the homogeneously broadened nuclear spin resonance in a crystal. We employ a combinatorial method to restrict the nuclear states to a fixed polarization and show that the center of the resonance is shifted linearly with the nuclear polarization by up to the zero polarization line width. The width shrinks from its maximum value at zero polarization to zero at full polarization. This suggests to use the line shape as a direct measure of nuclear polarization reached under dynamical pumping. In the limit of single quantum of excitation above the fully ferromagnetic state, we provide an explicit solution to the problem of nuclear spin dynamics which links a bound on the fastest decay rate to the observable width of the resonance line.