Achieving switchable and diversified functionalities in a single metasurface has garnered great research interest for potential terahertz applications. Here, we propose and demonstrate a phase-change metasurface that simultaneously supports broadband electromagnetically induced transparency (EIT) and broadband nearly perfect absorption, depending on the phase state of a phase change material-vanadium dioxide (VO2). The phase-change metasurface is composed of a VO2 nanofilm, a quartz spacer and gold split-square-ring resonators with VO2 nanopads embedded into the splits. When VO2 is in its insulating phase at room temperature, a broadband EIT window (maximum transmittance reaching 83%) with a bandwidth of 0.27 THz (relative bandwidth 30%) can be observed. Alternatively, when VO2 transforms into its fully metallic phase, the EIT functionality will be switched off and instead, the metasurface operates as a broadband absorber with the total absorption exceeding 93% and a bandwidth of 0.5 THz (relative bandwidth 74%). The electric and magnetic field distributions indicate that the broadband EIT stems from the bright-bright mode coupling and the broadband absorption arises from the excitation and superposition of two resonances within a metal-insulator-metal cavity. The design scheme is scalable from terahertz to infrared and optical frequencies, enabling new avenues towards switchable and multifunctional meta-devices.

中文翻译：

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使用相变材料实现可切换和多功能的太赫兹超表面

在单个超表面中实现可切换和多样化的功能已经引起了潜在太赫兹应用的极大研究兴趣。在这里，我们提出并展示了一种相变超表面，它同时支持宽带电磁感应透明 (EIT) 和宽带近乎完美的吸收，这取决于相变材料二氧化钒 (VO2) 的相态。相变超表面由 VO2 纳米膜、石英垫片和金分裂方形环谐振器组成，其中 VO2 纳米垫嵌入到分裂中。当 VO2 在室温下处于绝缘相时，可以观察到带宽为 0.27 THz（相对带宽 30%）的宽带 EIT 窗口（最大透射率达到 83%）。或者，当 VO2 转变为完全金属相时，EIT 功能将被关闭，取而代之的是，超表面作为宽带吸收器运行，总吸收超过 93%，带宽为 0.5 THz（相对带宽 74%）。电场和磁场分布表明宽带 EIT 源于亮-亮模式耦合，宽带吸收源于金属-绝缘体-金属腔内两个共振的激发和叠加。该设计方案可从太赫兹扩展到红外和光学频率，为实现可切换和多功能元设备提供了新途径。电场和磁场分布表明宽带 EIT 源于亮-亮模式耦合，宽带吸收源于金属-绝缘体-金属腔内两个共振的激发和叠加。该设计方案可从太赫兹扩展到红外和光学频率，为实现可切换和多功能元设备提供了新途径。电场和磁场分布表明宽带 EIT 源于亮-亮模式耦合，宽带吸收源于金属-绝缘体-金属腔内两个共振的激发和叠加。该设计方案可从太赫兹扩展到红外和光学频率，为实现可切换和多功能元设备提供了新途径。