Quantum coherence of excitons strongly bound to the magnetic order

We explore the 2D van der Waals antiferromagnetic semiconductor, NiPS₃, which has been inferred to possess a long excitonic coherence, but has never been measured directly. In addition, its excitons have shown strong coupling to the antiferromagnetic order. The material's exciton possesses a very narrow photoluminescence (PL) linewidth of about 350 μeV, indicating a narrow homogeneous linewidth and long excitonic coherence. Therefore, we employ ultrafast spectroscopy to measure the dephasing time, and its relation to the radiative recombination time. We utilized magnetic field-dependent polarization absorption measurements to conclude the system possesses subcomponents of the excitonic transition originating from three equivalent orientations of Néel vectors. Four-wave mixing experiments were performed to determine the relation between the excitonic coherence and radiative lifetime for various polarizations.