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Quasiparticle-Continuum Level Repulsion in a Quantum Magnet



K. W. Plumb, Kyusung Hwang, Yiming Qiu, Leland Harriger, G. E. Granroth, Alexander I. Kolesnikov, G. J. Shu, F. C. Chou, Ch. Ruegg, Yong Baek Kim, Young-June Kim


When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticle in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in an open quantum system where a quasiparticle can spontaneously decay into many particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our high resolution neutron spectroscopy study of magnetic quasiparticles in a frustrated quantum magnet BiCu2PO6, we observe a renormalization of quastiparticle dispersion relation due to the presence of the continuum arising from the decay of another quasiparticle. Our results have a broad implication for understanding quantum dynamics of an open quantum dynamics of an open quantum systme.
Nature Physics


frustrated quantum magnet, continuum


Plumb, K. , Hwang, K. , Qiu, Y. , Harriger, L. , Granroth, G. , Kolesnikov, A. , Shu, G. , Chou, F. , Ruegg, C. , Kim, Y. and Kim, Y. (2016), Quasiparticle-Continuum Level Repulsion in a Quantum Magnet, Nature Physics, [online], (Accessed June 10, 2023)
Created February 29, 2016, Updated October 12, 2021