Van der Waals heterostructures have emerged as a versatile platform to study correlated and topological electron physics. Spectroscopy experiments in the THz regime are crucial since the energy of THz photons matches that of relevant excitations and charge dynamics. However, their micrometer size and complex (dual-)gated structures have challenged such measurements. Here, we demonstrate on-chip THz spectroscopy on a dual-gated bilayer graphene device at liquid helium temperature. To avoid unwanted THz absorption by metallic gates, we developed a scheme of operation by combining semiconducting gates and optically controlled gating. This allows us to measure the clean THz response of graphene without being affected by the gates. We observed the THz signatures of electric-field-induced bandgap opening at the charge neutrality. We measured Drude conductivities at varied charge densities and extracted key parameters including effective masses and scattering rates. This work paves the way for studying novel emergent phenomena in dual-gated two-dimensional materials.

中文翻译：

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用于低温下双门范德华异质结构的片上太赫兹光谱


范德华异质结构已成为研究相关和拓扑电子物理学的多功能平台。太赫兹范围内的光谱实验至关重要，因为太赫兹光子的能量与相关激发和电荷动力学的能量相匹配。然而，它们的微米尺寸和复杂的（双）门控结构对此类测量提出了挑战。在这里，我们演示了在液氦温度下双门双层石墨烯器件上的片上太赫兹光谱。为了避免金属门对不必要的太赫兹吸收，我们开发了一种将半导体门和光学控制门控相结合的操作方案。这使我们能够测量石墨烯的干净太赫兹响应，而不受栅极的影响。我们观察到电场诱导带隙在电荷中性处开路的太赫兹特征。我们测量了不同电荷密度下的 Drude 电导率，并提取了包括有效质量和散射率在内的关键参数。这项工作为研究双门二维材料中的新涌现现象铺平了道路。