  In a PN junction, the separation between positive and negative charges leads
to diode transport. In the past few years, the intrinsic diode transport in
noncentrosymmetric polar conductors has attracted great interest, because it
suggests novel nonlinear applications and provides a symmetry-sensitive probe
of Fermi surface. Recently, such studies have been extended to
noncentrosymmetric superconductors, realizing the superconducting diode effect.
Here, we show that, even in a centrosymmetric crystal without directional
charge separation, the spins of an antiferromagnet (AFM) can generate a spatial
directionality, leading to an AFM diode effect. We observe large
second-harmonic transport in a nonlinear electronic device enabled by the
compensated AFM state of even-layered MnBi2Te4. We also report a novel
electrical sum-frequency generation (SFG), which has been rarely explored in
contrast to the well-known optical SFG in wide-gap insulators. We demonstrate
that the AFM enables an in-plane field-effect transistor and harvesting of
wireless electromagnetic energy. The electrical SFG establishes a powerful
method to study nonlinear electronics built by quantum materials. The AFM diode
effect paves the way for potential device concepts including AFM logic
circuits, self-powered AFM spintronics, and other applications that potentially
bridge nonlinear electronics with AFM spintronics.
