Staggered spin susceptibility at a two-dimensional antiferromagnetic quantum critical point

We report on the finite temperature staggered spin susceptibility $\chi (Q)$ as a function of the mode-mode coupling constant $y_1$ in the self-consistent renormalization theory of two-dimensional antiferromagnetic spin fluctuations with zero-point quantum fluctuations just at the quantum critical point ($y_0$ = 0). We find that the value $y_1$ = 0.1 is a criterion to classify the effect of the zero-point spin fluctuations on the temperature dependence of $\chi (Q)$ into a Curie law for weak $y_1<$ 0.1 and a Curie-Weiss type or a power law type for strong $y_1>$ 0.1. The absence of a Curie-Weiss temperature can serve as an identifying criterion for QCP ($y_0$ = 0) in systems with weak mode-mode coupling ($y_1<$ 0.1). Experimental application on the $y_1$ classification is shown to several itinerant layered antiferromagnetic systems through an analysis of nuclear spin-lattice relaxation rates.