Low-dimensional antiferromagnetic fluctuations in the superconductor UTe2

We present inelastic-neutron-scattering measurements performed on a large single crystal (mass of 241 mg) of the new heavy-fermion superconductor UTe2 above [1] and below [2] its superconducting temperature. We confirm the presence of antiferromagnetic fluctuations with the incommensurate wavevector k1 = (0 0.57 0). We emphasize the low-dimensionality of the magnetic fluctuations, consequence of the ladder structure of the U atoms, which is indicated by weak correlations along the direction c. The absence or weakness of ferromagnetic fluctuations in our data is discussed. A phenomenological magnetic-exchange scheme, with intra-ladder ferromagnetic coupling and inter-ladder antiferromagnetic coupling along b, is proposed. A gap-opening of the antiferromagnetic fluctuations is observed in the superconducting phase. Our neutron-scattering data obtained from a unique single crystal are compared with data obtained using large assemblies of co-aligned single crystals [3,4]. A discussion about the possible signatures of the observed antiferromagnetic fluctuations in bulk electronic-transport and thermodynamic measurements, but also from NMR spectroscopy, is also proposed. These new data may stimulate the elaboration of new models based on magnetically-mediated pairing to describe superconductivity in UTe2.