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arXiv · 1012.0731

Distribution of NMR relaxations in a random Heisenberg chain

T. Shiroka·F. Casola·V. Glazkov·A. Zheludev·K. Prsa·H. -R. Ott·J. Mesot
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Abstract

Nuclear magnetic resonance (NMR) measurements of the 29Si spin-lattice relaxation time T1 were used to probe the spin-1/2 random Heisenberg chain compound BaCu2(Si(1-x)Gex)2O7. Remarkable differences between the pure (x = 0) and the fully random (x = 0.5) case are observed, indicating that randomness generates a distribution of local magnetic relaxations. This distribution, which is reflected in a stretched exponential NMR relaxation, exhibits a progressive broadening with decreasing temperature, caused by a growing inequivalence of magnetic sites. Compelling independent evidence for the influence of randomness is also obtained from magnetization data and Monte Carlo calculations. These results suggest the formation of random-singlet states in this class of materials, as previously predicted by theory.

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T. Shiroka, F. Casola, V. Glazkov, A. Zheludev, K. Prsa, H. -R. Ott, J. Mesot. 2011-04-06. Distribution of NMR relaxations in a random Heisenberg chain. https://doi.org/10.1103/physrevlett.106.137202

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