Feedback of Superconductivity on the Magnetic Excitation Spectrum of UTe2

We investigate the spin dynamics in the superconducting phase of UTe2 by triple-axis inelastic neutron scattering on a single crystal. At the wave-vector k(1) = (0, 0.57, 0), where the normal state antiferromagnetic correlations are peaked, a modification of the excitation spectrum is evidenced, on crossing the superconducting transition, with a reduction of the relaxation rate together with the development of an inelastic peak at Omega approximate to 1 meV. The low dimensional nature and the a-axis polarization of the fluctuations, that characterise the normal state, are essentially maintained below the superconducting transition. The high ratio Omega/k(B)T(sc) approximate to 7.2 contrasts with the most common behaviour in heavy fermion superconductors.