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Exotic spin dynamics in a two-dimensional quantum antiferromagnet near the quantum critical point

Tao Hong (Neutron Scattering Division, Oak Ridge National Laboratory)

Inelastic neutron scattering (INS) is a powerful tool to probe the exotic quantum phenomena in low-dimensional quantum spin systems. In this talk, I will first introduce a novel spin-1/2 two-dimensional coupled ladder antiferromagnet (dimethylammonium)(3,5-dimethylpyridinium) CuBr4 (C9,H18N2CuBr4), abbreviated as DLCB, near the quantum critical point at zero field and ambient pressure [1, 2]. After that, I will present the recent unpolarized and polarized INS studies on DLCB. In conjunction with theoretical calculations, our results show the exotic quantum effects in spin dynamics including evidences of the field-induced spontaneous (T=0 K) magnon decay in an applied transverse magnetic field [3] and observation of Higgs-like amplitude mode [4], which is characterized by amplitude fluctuation of the order parameter and roughly analogous to the Higgs boson in particle physics. Our work provides much-needed experimental insights to the understanding of these quantum many-body effects in low-dimensional antiferromagnets.

[1] F. Awwadi et al., Inorg. Chem. 47, 9327 (2008).
[2] T. Hong et al., Phys. Rev. B 89, 174432 (2014).
[3] T. Hong et al., Nat. Commun. 8, 15148 (2017).
[4] T. Hong et al., Nat. Phys. 13, 638 (2017).

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