Winkler, R.; Zulicke, U.
We develop a comprehensive quantitative theory for magnetoelectricity in magnetically ordered quasi-two-dimensional (quasi-2D) systems whereby in thermal equilibrium an electric field can induce a magnetization and a magnetic field can induce an electric polarization. This effect requires that both space-inversion and time-reversal symmetry are broken. Antiferromagnetic order plays a central role in this theory. We define a Nel operator such that a nonzero expectation value signals collin