An over‐coupled, thermally tunable metasurface reflect‐array that employs the phase change material Ge₂Sb₂Te₅ (GST) is presented. The metasurface is constructed from gap plasmon cavities in which GST is incorporated as the active switching medium. Upon annealing at 200 °C for 10 min, the GST layer undergoes a transition from the amorphous state to the crystalline state, and this leads to a unity‐order increase of the refractive index. This is accompanied by a spectral shift of 1.6 µm in the resonance wavelength of the plasmonic cavities, larger than their resonance linewidth of 1.2 µm. It is shown that the low material absorption of the GST layer enables operation of the metasurface in the desirable over‐coupled regime. The numerical analysis indicates that this facilitates large changes in the reflection phase (up to 270°) and amplitude. The work opens the possibility of creating efficient reconfigurable metasurfaces for various applications, including holographic displays and image sensors.

中文翻译：

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过度耦合的相变超颖表面，实现有效的反射相位调制

采用相变材料Ge ₂ Sb ₂ Te ₅的超耦合热可调超表面反射阵列（GST）。超表面由间隙等离激元腔构成，GST被并入其中作为有效的交换介质。在200°C下退火10分钟后，GST层经历了从非晶态到结晶态的转变，这导致了折射率的单位数量级增加。这伴随着等离子腔共振波长的1.6 µm光谱偏移，大于其共振线宽1.2 µm。结果表明，GST层的低材料吸收能力使超颖表面在理想的过度耦合状态下运行。数值分析表明，这有助于反射相位（最大270°）和振幅的大变化。这项工作开辟了为各种应用创建有效的可重构超颖表面的可能性，