MULTIPLE-QUANTUM NUCLEAR-MAGNETIC-RESONANCE IN ONE-DIMENSIONAL QUANTUM SPIN CHAINS

Multiple quantum (MQ) nuclear magnetic resonance (NMR) spin dynamics a re investigated analytically in infinite one-dimensional (1D) chains o f spins 1/2. The representation of spin 1/2 operators with fermion fie ld operators allows to calculate exactly the spin density operator, an d hence NMR observables, under a variety of different conditions for 1 D spin systems. The exact expressions are valid for all times and for a macroscopic number of coupled spins. The calculations for a ID spin system initially at thermal equilibrium, and evolving under a 2-quantu m/2-spin average dipolar Hamiltonian, in the presence of nearest-neigh bor dipolar interactions yield MQ NMR spectra with 0- and 2-quantum co herences only. For a nonequilibrium initial condition with transverse magnetization, the analogous spin dynamics calculations produce MQ NMR spectra with all possible coherences of odd orders. Calculations at t he level of perturbation theory, which include next-nearest-neighbor d ipolar interactions, generate MQ spectra with higher even order cohere nces for equilibrium initial condition and evolution under a 2-quantum /2-spin propagator. Consideration of multiple spin correlations, 0-qua ntum coherences, and rf pulse imperfections are also presented. The re levance and implications of these theoretical results for comparison w ith the recent MQ NMR experiments of Yesinowski et al. on materials wi th quasi-one-dimensional distributions of spins, and for MQ NMR of sol ids in general are discussed. (C) 1997 American Institute of Physics.