Spin gap in a quasi-one-dimensionalS=12antiferromagnet:Cu

Abstract

Cu 2 ͑1,4-diazacycloheptane͒ 2 Cl 4 contains double chains of spin-1 2 Cu 2ϩ ions. We report ac susceptibility, specific heat, and inelastic neutron-scattering measurements on this material. The magnetic susceptibility (T) shows a rounded maximum at Tϭ8 K indicative of a low-dimensional antiferromagnet with no zero-field magnetic phase transition. We compare the (T) data with exact diagonalization results for various onedimensional spin Hamiltonians and find excellent agreement for a spin ladder with intrarung coupling J 1 ϭ1.143(3) meV and two mutually frustrating interrung interactions J 2 ϭ0.21(3) meV and J 3 ϭ0.09(5) meV. The specific heat in zero field is exponentially activated with an activation energy ⌬ϭ0.87(1) meV. A spin gap is also found through inelastic neutron scattering on powder samples that identify a band of magnetic excitations for 0.8ϽបϽ1.5 meV. Using sum rules we derive an expression for the dynamic spin-correlation function associated with noninteracting propagating triplets in a spin ladder. The Van Hove singularities of such a model are not observed in our scattering data, indicating that magnetic excitations in Cu 2 ͑1,4-diazacycloheptane͒ 2 Cl 4 are more complicated. For magnetic fields above H c1 Ӎ7.2 T specific-heat data versus temperature show anomalies indicating a phase transition to an ordered state below Tϭ1 K. ͓S0163-1829͑98͒05810-X͔ SPIN GAP IN A QUASI-ONE-DIMENSIONAL Sϭ 1 2 . . .

Weak spin interactions in Mott insulating La2O2Fe2OSe2McCabe1, Stock2, Rodriguez3 et al. 2014Phys. Rev. B4527630View full textAdd to dashboardCite

“…The intensity distribution at the gap edge is sensitive to the dimensionality of the interactions and can be quantified through use of the first moment sum rule. Figure 3(d) shows a comparison of the momentum-integrated intensity with calculations based on the single-mode approximation for an isotropic dispersion in a one-dimensional (1D) chain, 2D plane, or 3D structure [36][37][38]. The 2D model gives the best description consistent with the 2D-Ising critical properties discussed above.…”

Quantum phases and phase transitions of Mott insulators

“…While a quantitative synthesis of theory and experiment in the superconducting materials remains elusive, much progress has been made in describing a number of antiferromagnetic Mott insulators. A number of such insulators have been studied extensively in the past decade, with a few prominent examples being CaV 4 O 9 [1], (C 5 H 12 N 2 ) 2 Cu 2 Cl 4 [2,3,4], SrCu 2 (BO 3 ) 2 [5,6], TlCuCl 3 [7,8,9,10], and Cs 2 CuCl 4 [11,12]. In some cases, it has even been possible to tune these insulators across quantum phase transitions by applied pressure [8] or by an applied magnetic field [3,4,7,9].…”

Observation of Field-Induced Transverse Néel Ordering in the Spin Gap System TlCuCl3

“…Field-induced 3D ordering has been observed in several quasi-one-dimensional spin gap systems. [2][3][4][5][6] This paper is concerned with field-induced magnetic ordering in TlCuCl 3 . This compound has a monoclinic structure (space group P 2 1 /c).…”

“…In order to confirm the transverse spin ordering corresponding to the off-diagonal long-range order of the BEC, and to investigate the temperature and field dependence of the transverse magnetization m ⊥ corresponding to the condensate density n c , we performed neutron elastic scattering experiments on TlCuCl 3 .…”