  The respective unique merit of antiferromagnets and two-dimensional (2D)
materials in spintronic applications inspire us to exploit 2D antiferromagnetic
spintronics. However, the detection of the N\'eel vector in 2D antiferromagnets
remains a great challenge because the measured signals usually decrease
significantly in the 2D limit. Here we propose that the N\'eel vector of 2D
antiferromagnets can be efficiently detected by the intrinsic nonlinear Hall
(INH) effect which exhibits unexpected significant signals. As a specific
example, we show that the INH conductivity of the monolayer manganese
chalcogenides Mn$X$ ($X$=S, Se, Te) can reach the order of nm$\cdot$mA/V$^2$,
which is orders of magnitude larger than experimental values of paradigmatic
antiferromagnetic spintronic materials. The INH effect can be accurately
controlled by shifting the chemical potential around the band edge, which is
experimentally feasible via electric gating or charge doping. Moreover, we
explicitly demonstrate its $2\pi$-periodic dependence on the N\'eel vector
orientation based on an effective $k.p$ model. Our findings enable flexible
design schemes and promising material platforms for spintronic memory device
applications based on 2D antiferromagnets.
