High-sensitivity gas sensor by reflective spin splitting from antiferromagnetic film with inserted nematic liquid-crystal arrays

With the spread of environmental pollution around the world, the development of high-sensitivity gas sensors for monitoring human health has become crucial. A magnetic hyperbolic metamaterial (MM) structure is designed, where an antiferromagnetic film (AF) contains periodic arrays of nematic liquid crystals (NLCs). The orientation of NLCs situated within the incident plane can be precisely controlled by static electric fields, enabling them to align parallel or perpendicular to the surface, respectively. Dual control of in-plane spin-splitting is investigated, leveraging the magnetically tunable hyperbolic properties and the electrically controllable orientation of NLC molecules. A pronounced asymmetric spin splitting is observed, moreover, precise adjustment for the filling ratio between the NLC and AF enables switching between hyperbolic and elliptical phases. The contribution to the maximum spin-splitting of the AF and NLCs, respectively, is analyzed in depth. A NLC/AF MM-based gas sensor utilizing the in-plane spin-splitting of the left-handed circularly polarized component is proposed, with the capability to detect refractive indices from $\text{1.00027281}$ to $\text{1.0036}$. Taking sulfur dioxide (SO₂) and carbon dioxide (CO₂) as examples, the refractive index sensitivity of $\text{2.76}\times {\text{10}}^{\text{6}}{\lambda }_{\text{0}}$ and $\text{6.88}\times {\text{10}}^{\text{7}}{\lambda }_{\text{0}}$ can be achieved, respectively. It opens up a new way for the development of high-performance gas sensors in THz.