Overview
This study investigates giant nonlinear optical magnetochirality in a centrosymmetric two-dimensional (2D) ferrotoroid, specifically bilayer (2L) CrSBr. The research focuses on the emergence of magnetically switchable chiral light emission, addressing challenges in achieving dynamic tunability and polarization contrast in conventional opto-spintronics strategies. The findings indicate that a field-induced spin-canting state breaks the parity-time (PT) symmetry of the unperturbed antiferromagnetic (AFM) ground state in 2L CrSBr, leading to the activation of a spin-chirality-driven i-type susceptibility. The coherent interference between this emergent i-type susceptibility and intrinsic c-type second-harmonic generation (SHG) susceptibilities produces a macroscopic circularly polarized SHG signal with magnetically switchable helicity.
Research Context
Achieving magnetically switchable chiral light emission is identified as an important objective for 2D opto-spintronics. Traditional approaches for this goal reportedly face a fundamental trade-off between dynamic tunability and polarization contrast. Nonlinear optics, particularly through the mechanism of chiral SHG, is proposed as a distinct strategy to bypass this restriction. However, the experimental realization of this strategy has been described as elusive due to stringent symmetry requirements.
Approach
The study utilized bilayer (2L) CrSBr, characterized as a centrosymmetric 2D ferrotoroid. The approach involved inducing a spin-canting state through the application of an external field. This field-induced state was observed to break the PT symmetry of the unperturbed AFM ground state. The consequences of this symmetry breaking were then evaluated in the context of nonlinear optical responses, specifically focusing on second-harmonic generation (SHG). The research analyzed the interplay between the emergent spin-chirality-driven i-type susceptibility and intrinsic c-type SHG susceptibilities. Furthermore, the sensitive nature of the observed mechanism was leveraged to investigate remanent magnetic states after field saturation, which were reportedly undetectable by conventional linear probes. The non-volatility of these identified states was then exploited to demonstrate magneto-optical memory and logic operations.
Findings
- Giant nonlinear optical magnetochirality was observed in bilayer (2L) CrSBr, a centrosymmetric 2D ferrotoroid.
- A field-induced spin-canting state in 2L CrSBr was found to break the parity-time (PT) symmetry of its unperturbed antiferromagnetic (AFM) ground state.
- This symmetry breaking activated a spin-chirality-driven i-type susceptibility.
- The coherent interference between this emergent i-type and intrinsic c-type SHG susceptibilities generated a macroscopic circularly polarized SHG signal.
- The helicity of this circularly polarized SHG signal was demonstrated to be magnetically switchable.
- The mechanism enabled the uncovering of remanent magnetic states after field saturation, which evaded conventional linear probes.
- The non-volatility of these remanent magnetic states allowed for the demonstration of magneto-optical memory and logic operations.
Why This Matters
This work establishes a general symmetry-driven strategy for tailoring nonlinear magnetochirality. It also provides a sensitive optical probe for subtle spin textures within the 2D limit. The ability to achieve magnetically switchable chiral light emission bypasses previous limitations related to dynamic tunability and polarization contrast. The demonstration of magneto-optical memory and logic operations leveraging the non-volatility of remanent magnetic states suggests potential for device applications.