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위상양자물성 연구실에서 Materials Science and Technology Division, Oak Ridge National Laboratory의 도승환 박사님을 초청하여 아래와 같이 세미나를 개최합니다.

학과 구성원 여러분의 많은 참여를 부탁 드립니다.


○ Topic: Longitudinal magnon decay in the quasi-two-dimensional antiferromagnet in Ba2FeSi2O7


○ Speaker: 도  승  환  박사님 (Materials Science and Technology Division, Oak Ridge National Laboratory)


○ Date/time: 2022. 5. 10. (Tue.) 4:00 PM


○ Place: Natural Science 1,  Room No. 31317


○ 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 mode types are important. This talk will focus on this problem through a combined experimental and theoretical study of interacting transverse and longitudinal modes in an S=1 easy-planar quantum magnet, Ba2FeSi2O7 [1,2]. Our inelastic neutron scattering measurements show that Ba2FeSi2O7 is a quasi-two-dimensional antiferromagnet with large single-ion anisotropy (D>5J), and the extended spin wave theory analysis demonstrates its close proximity to a quantum critical point. The measured spectrum reveals 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 where the decay channels to the transverse modes are most active. A generalization of the standard spin-wave theory is used to account for the many-body effects of the interacting transverse and longitudinal modes in Ba2FeSi2O7. The measured mode decay and renormalization are reproduced by including one-loop corrections, where the kinematic conditions for the interactions are satisfied. Finally, the kinematic condition becomes violated in magnetic field. Our field inelastic neutron scattering measurement reveals that the longitudinal mode evolves into a long-lived quasi-particle in magnetic fields, demonstrating that this quantum many-body effect is tunable [3].

[1] S.-H. Do, H. Zhang, et al., Nat. Commun. 12 5331 (2021)
[2] T.-H. Jang, S.-H. Do et al., PRB 104 214434 (2021)
[3] S.-H. Do et al., (in preparation)

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