Staggered Spin Susceptibility at a Two-Dimensional Antiferromagnetic Quantum Critical Point

We report on the finite temperature staggered spin susceptibility χ(Q) as a function of the mode–mode coupling constant y1 in the self-consistent renormalization theory of two-dimensional antiferromagnetic spin fluctuations with zero-point quantum fluctuations just at the quantum critical point (y0 = 0). We find that the value y1 = 0.1 is a criterion to classify the effect of the zero-point spin fluctuations on the temperature dependence of χ(Q) into a Curie law for weak y1< 0.1 and a Curie–Weiss type or a power law type for strong y1> 0.1. The absence of a Curie–Weiss temperature can serve as an identifying criterion for QCP (y0 = 0) in systems with weak mode–mode coupling (y1< 0.1). Experimental application on the y1 classification is shown to several itinerant layered antiferromagnetic systems through an analysis of nuclear spin–lattice relaxation rates.