"Collective excitation continuum in the antiferromagnetic heavy-fermion system U2Zn17"
Our best knowledge of magnetic interactions and dynamics stems from experiments and theories on long-range ordered magnets. Protected by symmetry-breaking, magnetic excitations form spin waves with a dispersion relation that reflects the underlying interactions. This scenario, however, breaks down in at least two situations, namely, in frustrated magnets with competing exchange interactions, or in the presence of strong charge fluctuations that renormalize spin fluctuations. In this talk, I will give a brief overview of my experimental research themed around the breakdown of conventional ordering. The rest of the talk will specifically focus on the unusual spin dynamics in antiferromagnetic heavy-fermion metal U2Zn17. For U2Zn17, our inelastic neutron scattering experiments covered three decades of energy scale and documented no signatures of coherent magnons but only continuum of spin fluctuations in the antiferromagnetic state below TN = 9.7K, which persists in the paramagnetic state up to at least T = 2TN. With a dominantly transverse nature, the collective excitation demonstrates a correlation length of 13 Å at the low-energy limit with no gap observed down to 0.1meV. Spin fluctuation is isotropic in three-dimension up to 3meV, but correlation in the basal plane vanishes above 5meV, while that along the c-axis persists at 20meV (~20TN) up to the second nearest-neighbor in the c-direction. The documented excitation continuum is indicative of U2Zn17 as a spin system with dominating one-dimensional accompanied by frustrated inter-chain exchange interactions mediated by conduction electrons, which is qualitatively confirmed by a DFT+U computation.
