Quasi-Two-Dimensional Antiferromagnetic Spin Fluctuations in the Spin-Triplet Superconductor Candidate CeRh2As2

The tetragonal heavy-fermion superconductor CeRh2As2 (Tc=0.3 K) exhibits an exceptionally high critical field of 14 T for B∥c. It undergoes a field-driven first-order phase transition between superconducting states, potentially transitioning from spin-singlet to spin-triplet superconductivity. To further understand these superconducting states and the role of magnetism, we probe spin fluctuations in CeRh2As2 using neutron scattering. We find dynamic (π,π) antiferromagnetic (AFM) spin correlations with an anisotropic quasi-two-dimensional correlation volume. Our data place an upper limit of 0.31 μB on the staggered magnetization of corresponding Néel orders at T=0.08 K. Density functional theory calculations, treating Ce 4f electrons as core states, show that the AFM wave vector connects significant areas of the Fermi surface. Our findings indicate that the dominant excitations in CeRh2As2 for ℏω<1.2 meV are magnetic and suggest that superconductivity in CeRh2As2 is mediated by AFM spin fluctuations associated with a proximate quantum critical point.