title: Distribution of NMR relaxations in a random Heisenberg chain.
abstract: NMR measurements of the (29)Si spin-lattice relaxation time T(1) were used to probe the spin-1/2 random Heisenberg chain compound BaCu(2)(Si(1-x)Ge(x))(2)O(7). Remarkable differences between the pure (x=0) and the fully random (x=0.5) cases 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.
authors.affiliation: Laboratorium für Festkörperphysik, ETH Hönggerberg, CH-8093 Zürich, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Shiroka
authors.forename: F
authors.initials: F
authors.lastname: Casola
authors.forename: V
authors.initials: V
authors.lastname: Glazkov
authors.forename: A
authors.initials: A
authors.lastname: Zheludev
authors.forename: K
authors.initials: K
authors.lastname: Prša
authors.forename: H-R
authors.initials: HR
authors.lastname: Ott
authors.forename: J
authors.initials: J
authors.lastname: Mesot