Time reversal invariance and the nuclear quadrupole spin-lattice relaxation tensor

Abstract

A theoretical study is made of the nuclear electric quadrupole spin-lattice relaxation in solids, for the case where the quadrupole interaction is small compared with the Zeeman interaction. It is shown that, provided the external magnetic field H0 has no effect on the lattice motions which cause the relaxation, the principle of time reversal invariance implies that the nuclear quadrupole spin-lattice relaxation tensor is real and the relaxation probabilities W1 and W2 are invariant with respect to reversal of H0. If the magnetic field does influence the 'lattice', it is found that W1 and W2 are still invariant with respect to reversal of H0 even though the relaxation tensor is not necessarily real. A simple, classical model is presented to illustrate the results obtained quantum mechanically. Finally, it is shown that the anomalous orientation dependence of W2/W1 recently observed for 23Na in NaNO3 cannot be attributed to failure of the principle of time reversal invariance.