Two-dimensional transition metal dichalcogenides are promising candidates for ultrathin light modulators due to their highly tunable excitonic resonances at visible and near-infrared wavelengths. At cryogenic temperatures, large excitonic reflectivity in monolayer molybdenum diselenide (MoSe₂) has been shown, but the permittivity and index modulation have not been studied. Here, we demonstrate large gate-tunability of complex refractive index in monolayer MoSe₂ by Fermi level modulation and study the doping dependence of the A and B excitonic resonances for temperatures between 4 and 150 K. By tuning the charge density, we observe both temperature- and carrier-dependent epsilon-near-zero response in the permittivity and transition from metallic to dielectric near the A exciton energy. We attribute the dynamic control of the refractive index to the interplay between radiative and non-radiative decay channels that are tuned upon gating. Our results suggest the potential of monolayer MoSe₂ as an active material for emerging photonics applications.

中文翻译：

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单层二硒化钼的折射率调制

二维过渡金属二硫属化物是超薄光调制器的有希望的候选者，因为它们在可见光和近红外波长下具有高度可调的激子共振。在低温下，单层二硒化钼 (MoSe ₂ ) 中的激子反射率大，但尚未研究介电常数和折射率调制。在这里，我们展示了单层 MoSe ₂中复折射率的大栅极可调性通过费米能级调制并研究 A 和 B 激子共振在 4 到 150 K 之间的温度下的掺杂依赖性。从 A 激子能量附近的金属到电介质。我们将折射率的动态控制归因于在选通时调谐的辐射和非辐射衰减通道之间的相互作用。我们的结果表明单层 MoSe ₂作为新兴光子学应用的活性材料的潜力。