Evidence of anomalous Curie constants for nonmagnetic impurities in a critical 2-dimensional JQ₃ model on the honeycomb lattice

The Curie constants C^∗=lim_T→0Tχ_imp of a spin-1/2 and a spin-1 impurities are calculated using the quantum Monte Carlo simulations. Here the impurity susceptibility χ_imp is the difference between the uniform susceptibilities with and without the impurity and T is the temperature. The two-dimensional quantum JQ₃ model on the honeycomb lattice is considered as the host system, and Tχ_imp as a function T is investigated in great detail. Remarkably, our data indicates strongly that C^∗>0.25 and C^∗>2/3 for the spin-1/2 and the spin-1 impurities, respectively. In particular, although no definite conclusion is obtained due to finite-size effects, we find that the Curie constant associated with a spin-1/2 impurity likely converges to a value greater than the established result of 0.262(2) in the literature. The outcomes reached here provide certain evidence that fractional impurity spin is observed for the studied JQ₃ system.