LOW-FREQUENCY EXCITATIONS IN SR14CU24O41 FROM CU-63 ZEEMAN PERTURBED NQR

The authors report on (CU)-C-63 Zeeman-perturbed nuclear quadrupole re sonance (NQR) spin-lattice relaxation measurements in Sr14CU24O41 The measurements were performed for field intensities varying from 40 G up to 9.4 T, allowing a careful study of the low-frequency excitations i n the S=1/2 two-leg-ladder and chains present in this compound. The re laxation of Cu-63(2) nuclei in the ladder is dominated at low temperat ures by a very-low-frequency dynamic, possibly related to the slowing down of the spin fluctuations around a localized hole. At high tempera tures, where this contribution is negligible, one observes 1/T-1 diver ging logarithmically with decreasing field intensity. These observatio ns are discussed within the framework of recent theoretical models and a comparison with the corresponding results for the chain (CU)-C-63(1 ) nuclei is presented.