Babicheva Viktoriia E, Rumi Mariacristina
Department of Electrical and Computer Engineering, University of New Mexico Albuquerque New Mexico 87131 USA
Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB Ohio 45433 USA.
RSC Adv. 2024 Oct 25;14(46):33906-33918. doi: 10.1039/d4ra05149a. eCollection 2024 Oct 23.
We computationally analyze the electro-optic response of metasurfaces consisting of interconnected nanoantennas with multipolar resonances using a chalcophosphate, SnPS, as the active material. SnPS has large electro-optic coefficients and relatively low Curie temperature (<70 °C), allowing for strong changes in the refractive index of the material under moderate electric fields if the temperature can be finely controlled in proximity of the Curie point. Through numerical simulations, we show that metasurfaces designed with this nanostructured material demonstrate a significant shift of multipolar resonances upon biasing, despite moderate refractive-index values of the chalcophosphate and reduced mode localization due to this. The magnetic octupolar resonance of a dense array provides the strongest shift of spectral features upon changes in the refractive index, and we attribute it to the high mode localization of this higher-order multipole. We numerically demonstrate that narrow lattice resonances of collective nature do not provide an advantage in shifting the spectral features because of the nonlocal and delocalized nature of the modes, which are spread in the nanoantenna surrounding rather than confined inside nanoantennas. Both in-plane and out-of-plane biasing of the chalcophosphate crystals are similarly efficient with suitable electrode design, choice of electrode material, and crystal orientation within the nanoantennas. These designs exhibit optical properties similar to those of metasurfaces with isolated nanoantennas in the dense array.
我们使用硫代磷酸锡（SnPS）作为活性材料，通过计算分析了由具有多极共振的互连纳米天线组成的超表面的电光响应。SnPS具有较大的电光系数和相对较低的居里温度（<70°C），如果能在居里点附近精确控制温度，那么在中等电场下材料的折射率会发生显著变化。通过数值模拟，我们表明，尽管硫代磷酸盐的折射率适中且由此导致模式局域化降低，但用这种纳米结构材料设计的超表面在偏置时仍表现出多极共振的显著偏移。密集阵列的磁八极共振在折射率变化时提供了最强的光谱特征偏移，我们将其归因于这种高阶多极的高模式局域化。我们通过数值证明，由于模式的非局域和离域性质，其在纳米天线周围传播而非局限于纳米天线内部，因此集体性质的窄晶格共振在光谱特征偏移方面没有优势。通过合适的电极设计、电极材料选择以及纳米天线内的晶体取向，硫代磷酸锡晶体的面内和面外偏置同样有效。这些设计展现出与密集阵列中具有孤立纳米天线的超表面相似的光学特性。
