Dresden 2014 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 44: Spin Torque and Spin Excitations II
MA 44.6: Vortrag
Donnerstag, 3. April 2014, 16:15–16:30, HSZ 403
Novel spin excitations in the quasi-1D Haldane chain SrNi2V2O8 under magnetic field — •Anup K. Bera1, Bella Lake1, Nazmul Islam1, Bastian Klemke1, Joseph M. Law2, Astrid Schneidewind3, Jitae Park3, and Elisa Wheeler4 — 1Helmholtz-Zentrum Berlin, Berlin, Germany — 2Helmholtz-Zentrum Dresden Rossendorf, Dresden, Germany — 3Forschungs-Neutronenquelle Heinz Maier-Leibnitz, Garching, Germany — 4Institut Laue-Langevin, Grenoble, France
Spin-1 Heisenberg antiferromagnetic chains (Haldane chains) demonstrate novel behaviors where quantum fluctuations destroy long-range order (LRO) even at T = 0. They have spin singlet ground state and gapped magnon (S=1) excitations. Applied magnetic fields suppress zero-point fluctuations, and restore a gapless spectrum. The result is a quantum phase transition at a critical field Hc, to a magnetized state. The presence of anisotropy and interchain interactions lead to more complex behavior and a richer phase diagram.
Spin excitations have been investigated experimentally on the model compound SrNi2V2O8 having substantial interchain interactions and single-ion anisotropy. Field-induced 3D magnetic ordering has been found with two critical fields (12 T for H ⊥ c and 20.8 T H ∥ c at 4.2 K, respectively). For H ⊥ c, neutron scattering reveal (i) a unique field dependence of the gapped triplet excitations at H<Hc, (ii) gapless excitations at Hc, and (iii) the reappearance of gapped excitations at H>Hc. The dispersion at H=Hc is gapless and linear, in contrast to the gapped and quadratic dispersions at both H>Hc and H<Hc.