Floquet theory in solid-state nuclear magnetic resonance

The application of Floquet theory in solid-state nuclear magnetic resonance is discussed. The Floquet approach has been used in the study of various effects related to quadrupolar nuclei varying from the basic magic-angle spinning (MAS) Hamiltonian, rotational resonance, and rotary-resonance conditions to the effect of quadrupole nuclei on spin 1/2 coupled to them. An extension of Floquet theory, multimode-multipole Floquet theory (MMFT), in which a multipole operator basis has been used is applied to the analysis of heteronuclear decoupling, the calculation of the R² condition width, and depolarization effects in double-quantum recoupling experiments. Cross polarization (CP) is one of the most important techniques for the detection of rare spins in solid-state nuclear magnetic resonance (NMR). MAS leads to improvement in the spectral resolution making the various sites distinguishable and improving the signal to noise ratio but it complicates the analysis of the spectra resulting from dynamic processes.