The recent development of artificially fabricated van der Waals nanostructures makes it possible to design and control the symmetry of solids and to find novel physical properties and related functionalities. A characteristic physical property reflecting such symmetry breaking is the nonlinear response, which is typically studied as the second harmonic generation of light, although studies have recently expanded to include various transport phenomena. An important aspect of nonlinear transport for modern condensed matter physics is that it is not only a unique functionality of noncentrosymmetric systems but also an emergent property reflecting underlying physics such as spin–orbit interaction, superconductivity, magnetism, and band geometry/topology.

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