Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

Tao Hong, Masashige Matsumoto, Yiming Qiu, Wangchun Chen, Thomas R. Gentile, Shannon Watson, Firas F. Awwadi, Mark M. Turnbull, Sachith E. Dissanayake, Harish Agrawal, Rasmus Toft-Petersen, Bastian Klemke, Kris Coester, Kai P. Schmidt, David A. Tennant

Research output: Contribution to journalLetterpeer-review


Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed-matter physics1-3. The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu-Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics4,5, is prone to decay into a pair of low-energy Nambu-Goldstone modes in low dimensions2,6,7. Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using inelastic neutron scattering and applying the bondoperator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S = 1/2 quantum antiferromagnet C9H18N2CuBr4 near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.
Original languageEnglish
JournalNature Physics
Issue number7
Pages (from-to)638-642
Publication statusPublished - 2017
Externally publishedYes


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