Collective excitation continuum in the antiferromagnetic heavy-fermion system U₂Zn₁₇

We report the observation of a continuum of collective excitation in heavy-fermion antiferromagnet U₂Zn₁₇ from inelastic neutron scattering experiments, with no signatures of spin waves. The 13 Å near isotropic correlation length of these fluctuations implies they account for just 1% of the low-T Sommerfeld constant γ₀ = 200mJ/mol/ K² associated with heavy fermions. The magnetic excitations persist in the paramagnetic state up to 2T_N and the spectrum extends beyond an energy scale of 10T_N. These collective quantum fluctuations both within and beyond the ordered state of U2Zn17 are indicative of a strongly frustrated spin system ostensibly mediated by heavy fermions.