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

• Published in: Nature communications Vol. 12; no. 1; p. 5331
• Main Authors: Do, Seung-Hwan, Zhang, Hao, Williams, Travis J., Hong, Tao, Garlea, V. Ovidiu, Rodriguez-Rivera, J. A., Jang, Tae-Hwan, Cheong, Sang-Wook, Park, Jae-Hoon, Batista, Cristian D., Christianson, Andrew D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09-09-2021; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/2795; 639/766/119/997; Anisotropy; Antiferromagnetism; Brillouin zones; Decay; Energy; Humanities and Social Sciences; Inelastic scattering; Magnets; multidisciplinary; Neutron scattering; Neutrons; Phase transitions; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-25591-7

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.
Anisotropic spin
S
>1/2 quantum magnets can have multiple low energy modes. In this manuscript, the authors study the interaction of such low energy modes in the
S
 = 1 antiferromagnet Ba
2
FeSi
2
O
7
by combining neutron scattering measurements with an SU(3) generalization of the 1/
S
expansion.