Neutron scattering investigation of the spin density wave ground state in CeAuSb₂

CeAuSb₂ is a tetragonal heavy-fermion compound (s.g. P4/nmm) displaying exotic spin density wave (SDW) order below its Néel temperature T_N = 6 K. Magnetic field suppresses T_N toward absolute zero, but instead of reaching a quantum critical point, its SDW ground state evolves into a unique double-q magnetic order above B_c1 = 2.8 T. The magnetism may be coupled to nematic charge order induced by a structural transition just above T_N, and the coupling remains intact into the multi-q state [1]. Furthermore, earlier neutron diffraction [2] revealed a second harmonic Bragg peak below B_c1 suggesting the SDW is not a simple sinusoid. Even-order Bragg peaks have been associated with a SDW-induced lattice distortion, which can further be accompanied by a charge density wave. Its connection, if any, to a nematic state is an intriguing possibility. In this talk we will present recent zero-field magnetic neutron scattering measurements on a single crystal of CeAuSb₂. To address possible coupling of magnetic and charge orders, we performed polarized neutron diffraction in the SDW ground state. Additionally, we will present our results on magnetic critical scattering across the phase transition.

1. S. Seo et al, Phys Rev X 10, 011035 (2020)

2. G. Marcus et al, Phys Rev Lett 120, 097201 (2018)