Higgs (Amplitude) mode in a two-dimensional antiferromagnet

Low-dimensional transition metal oxides show many interesting phenomena ranging from classical magnetic ordering to high-temperature superconductivity. The magnetic properties of these oxides are generally described within the framework of conventional spin only Heisenberg model, as orbital degrees of freedom are often quenched.   In this talk, I will discuss novel, excitonic magnetism in the intermediate strength regime of spin-orbit coupling in Mott insulating two-dimensional antiferromagnet Ca2RuO4.  Spin wave dispersion, measured using the inelastic neutron scattering, shows a clear deviation from conventional Heisenberg magnet.  The excitations of the ordered antiferromagnetic phase consist of two transverse (Goldstone) modes, and a third mode which corresponds to the amplitude fluctuations (Higgs mode) of the moment.  At the AFM ordering wave-vector, the Higgs mode decays into a pair of Goldstone modes.  A quantitative understanding of the decay process has been achieved through a complete mapping of the transverse modes over the entire Brillouin zone.   

A. Jain, M. Krautloher, J. Porras, G. H. Ryu, D. P. Chen, D. L. Abernathy, J. T. Park, A. Ivanov, J. Chaloupka, G. Khaliullin, B. Keimer, and B. J. Kim,  Nature Physics advance online publication, 27 March 2017 doi:10.1038/nphys4077