title: NMR evidence for a "Generalized spin-peierls Transition" in the high-magnetic-field phase of the spin ladder Cu2(C5H12N2)2Cl4
abstract: The magnetic-field-induced 3D ordered phase of the two-leg spin ladder Cu2(C5H12N2)2Cl4 has been probed through measurements of 1H NMR spectra and 1/T1 in the temperature range 70 mK-1.2 K. The second order transition line T(c)(H) has been determined between H(c1) = 7.52 T and H(c2) = 13.5 T and varies as (H-H(c1))(2/3) close to H(c1). From the observation of anomalous shifts and a crossover in 1/T1 above T(c), the mechanism of the 3D transition is argued to be magnetoelastic as in spin-Peierls chains, here involving a displacement of the protons along the longitudinal exchange ( J( parallel)) path.
authors.affiliation: Laboratoire de Spectrometrie Physique, Universite J. Fourier, BP 87, F-38402 St. Martin d'Heres, France.
authors.initials: H
authors.lastname: Mayaffre
authors.initials: M
authors.lastname: Horvatic
authors.initials: C
authors.lastname: Berthier
authors.initials: MH
authors.lastname: Julien
authors.initials: P
authors.lastname: Segransan
authors.initials: L
authors.lastname: Levy
authors.initials: O
authors.lastname: Piovesana