Experimental Observation of Spin Defects in the van der Waals Material GeS₂

Spin defects in atomically thin two-dimensional (2D) materials are promising for quantum applications, particularly quantum sensing. The long coherence times of the spin defects enable high sensitivity in measurements of the fluctuations of the targeted physical parameters. However, the nuclear-spin bath remains a major source of decoherence. Here, we reveal the presence of optically addressable spin defects in germanium disulfide (β-GeS₂) characterized by a wide bandgap and potential nuclear-spin-free lattice. Coherent control of the spin defects has been successfully demonstrated, and the coherence time T₂ at 5 K can achieve tens of microseconds, 100 times that of a negatively charged boron vacancy (V_B^-) in hexagonal boron nitride. An optical-spin defect pair model proposed recently has been used to explain their dynamics. Finally, we use density functional theory calculations to propose possible candidate structures for the spin defects.