title: Competition between helimagnetism and commensurate quantum spin correlations in LiCu2O2.
abstract: Neutron diffraction and bulk measurements are used to determine the nature of the low-temperature ordered state in LiCu2O2, a S=1/2 spin-chain compound with competing interactions. The spin structure is found to be helimagnetic, with a propagation vector (0.5,zeta,0), zeta=0.174. The nearest-neighbor exchange constant and frustration ratio are estimated to be J(1)=5.8 meV and J(2)/J(1)=0.29, respectively. For idealized quantum spin chains, these parameter values would signify a gapped spin-liquid ground state with commensurate spin correlations. The observed temperature dependence of the magnetic propagation vector in LiCu2O2 is attributed to a competition between incommensurate helimagnetism in the classical spin model and commensurability in the quantum case. It is also proposed that long-range ordering in LiCu2O2 is facilitated by intrinsic nonstoichiometry.
authors.affiliation: Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6393, USA.
authors.forename: T
authors.initials: T
authors.lastname: Masuda
authors.forename: A
authors.initials: A
authors.lastname: Zheludev
authors.forename: A
authors.initials: A
authors.lastname: Bush
authors.forename: M
authors.initials: M
authors.lastname: Markina
authors.forename: A
authors.initials: A
authors.lastname: Vasiliev