The Groundbreaking Discovery of Nonlinear Magnetic Second Harmonic Generation in Monolayer CrPS4

In a groundbreaking discovery, a research team led by Professor Sheng Zhigao at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has observed strong nonlinear magnetic second harmonic generation (MSHG) induced by the ferromagnetic order in monolayer CrPS4. This discovery sheds light on the unexplored nonlinear optical properties of two-dimensional van der Waals materials, particularly the link between second harmonic generation (SHG) and magnetic order.

Second harmonic generation is a nonlinear optical effect that is sensitive to symmetry breaking in materials. While it was first observed in crystals with broken symmetry (i type), SHG also occurs in magnetic systems (c type) but is typically much weaker. This limitation has hindered the use of SHG in optical devices. The discovery of ferromagnetic order induced c type SHG effects in monolayer CrPS4 opens up new possibilities in optoelectronics.

In their study, Sheng’s team investigated the magnetic order-related SHG effects in the two-dimensional antiferromagnetic material CrPS4. They discovered that while antiferromagnetic order in bulk and even-layered CrPS4 did not produce c type SHG effects, a significant c type SHG effect was induced by monolayer ferromagnetic order in odd-layered CrPS4. This observation is the first of its kind and highlights the dual breaking of spatial and time inversion symmetries in 2D magnets.

The most significant finding of the research team is that the ferromagnetic order induced c type SHG in monolayer CrPS4 has a signal strength comparable to that of i type SHG, which arises from the breaking of crystal structural symmetry. This rarity among magnetic materials suggests a new avenue for the development of nonlinear optical devices based on 2D materials with magnetic order.

The discovery of strong nonlinear magnetic second harmonic generation induced by ferromagnetic order in monolayer CrPS4 represents a significant advancement in the field of nonlinear optics. This breakthrough not only expands our understanding of the relationship between SHG and magnetic order in two-dimensional materials but also opens up new possibilities for the design of future optoelectronic devices.