Static and magneto-optical Kerr effect measurements are used to investigate a host of kagome lattice helimagnets and topological magnetic materials. These measurements are performed at extremely high magnetic fields and as a function of temperature enabling us to investigate their full phase diagram.

Unlike these conventional excitons formed from extended Bloch states, excitonic bound states from intrinsically many body localized states are rare and peculiar. Such a spin–orbit-entangled exciton state appears below the Néel temperature of 150 K in NiPS3, an antiferromagnetic van der Waals material. This exciton is thought to arise intrinsically from the many-body states of the Zhang–Rice state. The excitonic transition shows an extremely narrow linewidth and was attributed to a transition from a Zhang–Rice triplet to a Zhang–Rice singlet.

These excitons are thought to be coupled to zigzag antiferromagnetic order in this layered antiferromagnetic insulator. The exciton exhibits a narrow photoluminescence linewidth of roughly ~350 μeV with near-unity linear polarization. Furthermore, this excitonic transition shows strong linear dichroism over a broad spectral range. In addition, over ten exciton-A1g-phonon bound states on the high-energy side of the exciton resonance were observed and were assigned to a strong modulation of the ligand-to-metal charge-transfer energy by electron–lattice interactions. By applying an in-plane magnetic field, manipulation of the photoluminescence polarization can be achieved. We combine different spectroscopic tools such as linear and time-resolved spectroscopy in magnetic fields up to 25 Tesla to understand the coherent properties of this exitonic transition. Magnetic field and temperature dependent four-wave mixing, and multidimensional spectroscopy measurements will be discussed.