Sign-resolved nanoscale readout and control of hidden antiferromagnetic spin order
Antiferromagnetic memories promise ultrafast, stray-field-free information storage. Yet perfect magnetic compensation conceals the information carrier itself: the sign of the Néel vector distinguishing two time-reversed states. Moreover, in future dense memories, the local polarity of Néel domains would need to be read out on the nanoscale. We make this hidden polarity visible in a fully-compensated, high-Néel-temperature, PT-symmetric antiferromagnet by driving interband electric-dipole transitions by mid-infrared near-fields confined at a scanning probe. The excitation generates a Néel-order-dependent quantum-metric photocurrent, a Hall-like signal reversing with Néel order, which we term the optical nonlinear anomalous Hall effect. This optically induced electrical readout maps opposite Néel polarities with sub-100-nm resolution at room temperature and, combined with spin-orbit-torque writing, reveals Néel-texture polarization and reversible domain-wall motion, establishing electrical-write/optoelectronic-read antiferromagnetic functionality.