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 describe the unusual spin dynamics in antiferromagnetic heavy-fermion metal U2Zn17, in which both two scenarios can be potentially relevant. Our inelastic neutron scattering experiments, covering three decades of energy scale, documented no signatures of magnons but only continuum of spin fluctuations in the antiferromagnetic state below TN = 9.7K. The excitation continuum persists in the paramagnetic state up to at least T = 2TN and carries a distinguished transverse nature as evidenced by its polarization-dependence. With no gap observed down to 0.1meV, the collective excitation demonstrates a correlation length of 13 Å at the low-energy limit, which is isotropic in three-dimension up to 3meV. Moving up in energy, correlation in the a-b plane gradually fades and vanishes above 5meV, while that along the c-axis persists at 20meV (~20TN) up to the second nearest-neighbor in the c-direction. The excitation continuum, collective and transverse in nature with no signatures of magnons and prevailing at energy and temperature much higher than TN, are indicative of U2Zn17 as a one-dimensional spin system whose low-energy dynamics are strongly modified by either frustrated two-dimensional interactions or the large density state of heavy fermions.
About the QSQM: The EFRC-QSQM center aims to develop and apply nontrivial quantum sensing to measure and correlate local and nonlocal quantum observables in exotic superconductors, topological crystalline insulators, and strange metals. The center is led by the University of Illinois at Urbana-Champaign in partnership with the University of Illinois at Chicago and the SLAC National Accelerator Laboratory.