In the 1H monolayer transition metal dichalcogenide, the inversion symmetry is broken, while the reflection symmetry is maintained. On the other hand, in the bilayer, the inversion symmetry is restored, but the reflection symmetry is broken. As a consequence of these contrasting symmetries, here we show that bilayer WS₂ exhibits a quantum confined Stark effect (QCSE) that is linear with the applied out-of-plane electric field, in contrast to a quadratic one for a monolayer. The interplay between the unique layer degree of freedom in the bilayer and the field driven partial interconversion between intralayer and interlayer excitons generates a giant tunability of the exciton oscillator strength. This makes bilayer WS₂ a promising candidate for an atomically thin, tunable electro-absorption modulator at the exciton resonance, particularly when stacked on top of a graphene layer that provides an ultrafast nonradiative relaxation channel. By tweaking the biasing configuration, we further show that the excitonic response can be largely tuned through electrostatic doping, by efficiently transferring the oscillator strength from neutral to charged exciton. The findings are prospective toward highly tunable, atomically thin, compact, and light, on chip, reconfigurable components for next generation optoelectronics.

中文翻译：

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双层WS _2中高度可调的层状激子：线性量子局限斯塔克效应与静电掺杂

在1H单层过渡金属二硫化二氢中，反转对称性破裂，同时保持了反射对称性。另一方面，在双层中，恢复了反演对称性，但是破坏了反射对称性。由于这些相反的对称性，在这里我们显示双层WS ₂表现出量子限制的斯塔克效应（QCSE），该效应与所施加的平面外电场呈线性关系，与单层的二次电场相反。双层中独特的层自由度与层内和层间激子之间的场驱动部分互转换之间的相互作用产生了激子振荡器强度的巨大可调性。这使得双层WS ₂激子共振时原子薄，可调谐电吸收调制器的一种有希望的候选者，特别是当堆叠在提供超快非辐射弛豫通道的石墨烯层上时。通过调整偏置结构，我们进一步表明，通过将振荡器的强度从中性激子转移到带电激子，可以通过静电掺杂对激子响应进行很大的调整。这些发现对于面向下一代光电子学的高度可调谐，原子薄，紧凑和轻巧的可重构组件具有前瞻性。