Second-Harmonic-Generation Effect and Giant Optical Birefringence in the Weyl Material CaAgAs

Area of Science:

• Materials Science
• Optics
• Solid State Physics

Background:

• Nonlinear-optical (NLO) materials are crucial for the 8-14 μm atmospheric transparent window.
• Arsenide materials show promise for NLO applications, but characterization challenges exist.
• Conventional powder second-harmonic-generation (SHG) techniques are difficult for narrow-band-gap materials.

Purpose of the Study:

• To address the need for NLO materials in the 8-14 μm atmospheric window.
• To develop a modified powder SHG measurement method for narrow-band-gap materials.
• To investigate the NLO properties of the novel arsenide Weyl material, CaAgAs.

Main Methods:

• Proposed and utilized a modified powder SHG measurement technique.
• Employed first-principles calculations to determine NLO coefficients.
• Investigated the structural and electronic properties of CaAgAs.

Main Results:

• Successfully observed the SHG signal in CaAgAs, approximately 0.7 times that of CdGeAs2.
• Calculated the largest SHG coefficient for CaAgAs to be 236 pm/V.
• Identified the crucial role of ionic bonds in the [Ca3As13] motif and distorted Kagome lattice for SHG.
• Predicted strong optical anisotropy and a giant optical birefringence of 0.52 for CaAgAs.

Conclusions:

• CaAgAs is a promising NLO material for the 8-14 μm atmospheric transparent window.
• The modified SHG method is effective for characterizing narrow-band-gap materials.
• The unique crystal structure of CaAgAs contributes significantly to its NLO properties.