Correlated excitonic signatures of individual van der Waals NiPS3 antiferromagnet nanoflakes

Composite quasi-particles with emergent functionalities in spintronic and quantum information science can be realized in correlated materials due to entangled charge, spin, orbital, and lattice degrees of freedom. Here we show that by reducing the lateral dimension of correlated antiferromagnet NiPS3 flakes to tens of nanometers and thickness to less than ten nanometers, we can switch-off the bulk spin-orbit entangled exciton in the near-infrared (1.47 eV) and activate visible-range (1.8-2.2 eV) transitions. These ultra-sharp lines (<120 mu eV at 4.2 K) share the spin-correlated nature of the bulk exciton by displaying a strong linear polarization below Neel temperature. Furthermore, exciton photoluminescence lineshape analysis indicates a polaronic character via coupling with at-least 3 phonon modes and a comb-like Stark effect through discretization of charges in each layer. These findings augment the knowledge on the many-body nature of excitonic quasi-particles in correlated antiferromagnets and also establish the nanoscale correlated antiferromagnets as a promising platform for integrated magneto-optic devices.