The recently discovered two-dimensional materials can be used to fabricate multilayer heterostructures. Interlayer charge transfer is a key process in such heterostructures as it can enable emergent optoelectronic properties. Efficient interlayer charge transfer in van der Waals heterostructures has been observed by femtosecond transient absorption and steady-state optical spectroscopy measurements, based on measuring the interlayer carrier distribution. Here, we show that a second harmonic generation process allows direct probing of the electric field induced by the charge transfer. An ultrashort laser pulse was used to excite electrons and holes in a MoS2/WS2 heterostructure. The separation of the electrons and holes from the two monolayers generates an electric field, which enables the generation of the second harmonic of an incident fundamental pulse. We further studied the time evolution of this electric field by measuring the second harmonic signal as a function of the time delay between the pump and the fundamental pulses. The result agrees well with the dynamics revealed by a transient absorption measurement. These results provide direct evidence of interlayer charge transfer and demonstrate an all-optical method of studying charge transfer and induced electric fields in two-dimensional materials. Furthermore, this effect, if large enough, could be utilized in optical devices based on 2D heterostructures with nonlinear optical responses controllable by interlayer charge transfer.The recently discovered two-dimensional materials can be used to fabricate multilayer heterostructures. Interlayer charge transfer is a key process in such heterostructures as it can enable emergent optoelectronic properties. Efficient interlayer charge transfer in van der Waals heterostructures has been observed by femtosecond transient absorption and steady-state optical spectroscopy measurements, based on measuring the interlayer carrier distribution. Here, we show that a second harmonic generation process allows direct probing of the electric field induced by the charge transfer. An ultrashort laser pulse was used to excite electrons and holes in a MoS2/WS2 heterostructure. The separation of the electrons and holes from the two monolayers generates an electric field, which enables the generation of the second harmonic of an incident fundamental pulse. We further studied the time evolution of this electric field by measuring the second harmonic signal as a function of the time delay between the pump an...

中文翻译：

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范德华异质结构中层间电荷转移的非线性光学效应

最近发现的二维材料可用于制造多层异质结构。层间电荷转移是这种异质结构中的关键过程，因为它可以实现新兴的光电特性。基于测量层间载流子分布，通过飞秒瞬态吸收和稳态光谱测量观察到范德华异质结构中的有效层间电荷转移。在这里，我们展示了二次谐波产生过程允许直接探测由电荷转移引起的电场。超短激光脉冲用于激发 MoS2/WS2 异质结构中的电子和空穴。电子和空穴从两个单层分离产生电场，这使得能够产生入射基波脉冲的二次谐波。我们通过测量二次谐波信号作为泵浦和基本脉冲之间的时间延迟的函数，进一步研究了该电场的时间演变。结果与瞬态吸收测量揭示的动力学非常吻合。这些结果提供了层间电荷转移的直接证据，并展示了一种研究二维材料中电荷转移和感应电场的全光学方法。此外，如果这种效应足够大，可用于基于二维异质结构的光学器件中，该二维异质结构具有可通过层间电荷转移控制的非线性光学响应。最近发现的二维材料可用于制造多层异质结构。层间电荷转移是这种异质结构中的关键过程，因为它可以实现新兴的光电特性。基于测量层间载流子分布，通过飞秒瞬态吸收和稳态光谱测量观察到范德华异质结构中的有效层间电荷转移。在这里，我们展示了二次谐波产生过程允许直接探测由电荷转移引起的电场。超短激光脉冲用于激发 MoS2/WS2 异质结构中的电子和空穴。电子和空穴与两个单层的分离会产生电场，从而能够产生入射基波脉冲的二次谐波。