Berlin 2018 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 6: Quantum Magnets and Molecular Magnets (joint session TT/MA)
TT 6.8: Talk
Monday, March 12, 2018, 11:30–11:45, H 3010
Alternating ferro- and antiferromagnetic Heisenberg chain: from dimer to Haldane limit — •Niklas Casper and Wolfram Brenig — Institute for Theoretical Physics, Technical University Braunschweig, Braunschweig, Germany
We present results of a study of the S=1/2 Heisenberg chain with alternating ferro- and antiferromagnetic exchange, J2 and J1 respectively. This system interpolates from a dimer to a Haldane chain as j=|J2/J1| varies from 0 to ∞. Using perturbation theory (PT) and quantum Monte Carlo based on the stochastic series expansion (SSE) method, we study elementary excitations, thermodynamic properties, and the dynamic structure factor S(q,ω). For j ≪ 1 we find good agreement between PT and SSE. For arbitrary j we show that S(q,ω), obtained from SSE, scales between triplons at j ≪ 1 and a Haldane chain spectrum at j ≫ 1. Finally, we contrast our findings for the spin gap versus j against existing literature.