A recent study led by Professor Sheng Zhigao at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has uncovered a remarkable phenomenon in the field of nonlinear optics. The research team has successfully observed the strong nonlinear magnetic second harmonic generation (MSHG) induced by ferromagnetic order in monolayer CrPS4, marking a significant advancement in the understanding of optical properties in magnetic materials.
Second harmonic generation (SHG) is a well-known nonlinear optical effect that is sensitive to symmetry breaking in materials. Initially observed in crystals with broken symmetry (i type), SHG also occurs in magnetic systems (c type), albeit with weaker effects. The limitations of SHG in magnetic materials have hindered their potential use in optical devices. The unique properties of two-dimensional van der Waals materials have drawn attention, but their nonlinear optical properties, particularly the relationship between SHG and magnetic order, remain largely unexplored.
Professor Sheng’s team focused on investigating the magnetic order-related SHG effects in the two-dimensional antiferromagnetic material CrPS4. Surprisingly, they found that in bulk and even-layered CrPS4, antiferromagnetic order did not exhibit significant c type SHG effects. However, an intriguing discovery occurred in odd-layered CrPS4, where a substantial c type SHG effect induced by monolayer ferromagnetic order was observed. This groundbreaking observation represents the first instance of ferromagnetic order inducing c type SHG effects in a 2D magnet under the electric-dipole approximation. The unique nature of this phenomenon stems from the simultaneous breaking of spatial and time inversion symmetries.
The research team’s findings have far-reaching implications in the field of nonlinear optics and magnetic materials. Notably, the ferromagnetic order induced c type SHG was found to have a signal strength comparable to that of i type SHG arising from the breaking of crystal structural symmetry. This rare occurrence challenges conventional notions about the limitations of c type SHG effects in magnetic materials and opens up new possibilities for leveraging magnetic properties in optoelectronic applications.
The discovery of strong nonlinear magnetic second harmonic generation induced by ferromagnetic order in monolayer CrPS4 represents a significant breakthrough in the field of nonlinear optics. The research not only sheds light on the intricate relationship between magnetic order and optical properties in two-dimensional materials but also paves the way for future advancements in the design of novel optoelectronic devices.
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