Decay and renormalization of a longitudinal mode in a quasi-two-dimensional antiferromagnet

Abstract

An ongoing challenge in the study of quantum materials, is to reveal and explain collective quantum effects in spin systems where interactions between different modes types are important. Here we approach this problem through a combined experimental and theoretical study of interacting transverse and longitudinal modes in an easy-plane quantum magnet near a continuous quantum phase transition. Our inelastic neutron scattering measurements of Ba${}_2$FeSi${}_{2}O$_{7}$ reveal the emergence, decay, and renormalization of a longitudinal mode throughout the Brillouin zone. The decay of the longitudinal mode is particularly pronounced at the zone center. To account for the many-body effects of the interacting low-energy modes in anisotropic magnets, we generalize the standard spin-wave theory. The measured mode decay and renormalization is reproduced by including all one-loop corrections. The theoretical framework developed here is broadly applicable to quantum magnets with more than one type of low energy mode.

29 pages, 8 figures in main text

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Cited by in corpus (8)

• Geometric integration of classical spin dynamics via a mean-field Schrödinger equation
• Langevin dynamics of generalized spins as SU($N$) coherent states
• Instabilities of heavy magnons in an anisotropic magnet
• Physical properties of a quasi-two-dimensional square lattice antiferromagnet Ba${}_2$FeSi${}_2$O${}_7$
• Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet C${}_9$H${}_{18}$N${}_2$CuBr${}_4$
• Field-induced spin level crossings within a quasi-XY antiferromagnetic state in Ba${}_2$FeSi${}_2$O${}_7$
• Classical dynamics of the antiferromagnetic Heisenberg $S=1/2$ spin ladder
• $SU(N)$ spin-phonon simulations of Floquet dynamics in spin $S>1/2$ Mott insulators