Nuclear spin-lattice relaxation in incommensurate systems

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Abstract
The temperature and frequency dependences of the spin-lattice relaxation rates of quadrupolar nuclei in incommensurate systems have been evaluated both for direct and for Raman processes in the plane wave and the multisoliton limits. In contrast to translationally periodic systems, the spin-lattice relaxation rate varies over the incommensurate NMR line and is determined by phason and amplitudon fluctuations. The average T1 should be anomalously short and nearly independent of temperature over the whole incommensurate phase, and should sharply increase at the lock-in transition reflecting the change in the phason spectrum. The variation of T1-1 over the incommensurate NMR line allows for a separate determination of the amplitudon and phason contributions as well as a discrimination between direct and Raman processes.