Propagating spinons and magnons in coupled quantum spin chains

Abstract:

In conventional magnets with magnetic long range order (LRO), low-energy excitations are carried by spin waves, represented by massless bosons called magnons with S = 1. However, in one-dimensional (1D) antiferromagnetic quantum spin systems, quantum fluctuations destroy LRO. Their low-energy excitations are spinons, a fractionalized fermion with S = 1/2, instead of magnons. In quasi-1D antiferromagnets with quantum spins, magnetic excitations are carried by either magnons or spinons in different energy regimes: they do not coexist independently, nor could they interact with each other. In this seminar, I will present our recent neutron scattering and theoretical studies of a unique quasi-1D quantum spin system, Cu₂(OH)₃Br, which consists of weakly-coupled, ferromagnetic and antiferromagnetic alternating chains. As a result, this system shows coexistence of two different magnetic quasiparticles: the ferromagnetic chains give rise to conventional magnon excitations, while the antiferromagnetic chains yield spinons. In addition, I will show that these magnetic quasiparticles interact via weak interchain interactions, leading to gap opening of magnetic excitations and asymmetric spectral weight.

Host: D. Inosov

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