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Bruognolo, Benedikt; Weichselbaum, Andreas; Delft, Jan von and Garst, Markus (2016): Dynamic structure factor of the spin-1/2 XXZ chain in a transverse field. In: Physical Review B, Vol. 94, No. 8, 85136

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The spin-1/2 XXZ chain with easy-plane anisotropy in a transverse field describes well the thermodynamic properties of the material Cs2CoCl4 in a wide range of temperatures and fields including the region close to the spin-flop Ising quantum phase transition. For a comparison with prospective inelastic neutron scattering experiments on this compound, we present results of an extensive numerical study of its dynamic structure factor S-alpha beta (k, omega) using matrix-product-state (MPS) techniques. Close to criticality, the dynamic part of the correlator S-xx longitudinal to the applied field is incoherent and possesses a small total weight as the ground state is already close to saturation. The transverse correlator S-zz, on the other hand, is dominated by a coherent single-particle excitation with additional spectral weight at higher energies that we tentatively attribute to a repulsively bound pair of particles. With increasing temperature, the latter quickly fades and spectral weight instead accumulates close to zero wave vector just above the single-particle energy. On a technical level, we compare the numerical efficiency of real-time evolution to an MPS-based Chebyshev expansion in the present context, finding that both methods yield results of similar quality at comparable numerical costs.

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