Boolakee Tobias, Heide Christian, Garzón-Ramírez Antonio, Weber Heiko B, Franco Ignacio, Hommelhoff Peter
Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
Nature. 2022 May;605(7909):251-255. doi: 10.1038/s41586-022-04565-9. Epub 2022 May 11.
Light-driven electronic excitation is a cornerstone for energy and information transfer. In the interaction of intense and ultrafast light fields with solids, electrons may be excited irreversibly, or transiently during illumination only. As the transient electron population cannot be observed after the light pulse is gone, it is referred to as virtual, whereas the population that remains excited is called real. Virtual charge carriers have recently been associated with high-harmonic generation and transient absorption, but photocurrent generation may stem from real as well as virtual charge carriers. However, a link between the generation of the carrier types and their importance for observables of technological relevance is missing. Here we show that real and virtual charge carriers can be excited and disentangled in the optical generation of currents in a gold-graphene-gold heterostructure using few-cycle laser pulses. Depending on the waveform used for photoexcitation, real carriers receive net momentum and propagate to the gold electrodes, whereas virtual carriers generate a polarization response read out at the gold-graphene interfaces. On the basis of these insights, we further demonstrate a proof of concept of a logic gate for future lightwave electronics. Our results offer a direct means to monitor and excite real and virtual charge carriers. Individual control over each type of carrier will markedly increase the integrated-circuit design space and bring petahertz signal processing closer to reality.
光驱动电子激发是能量和信息传递的基石。在强超快光场与固体的相互作用中，电子可能被不可逆地激发，或者仅在光照期间被瞬态激发。由于光脉冲消失后无法观察到瞬态电子数，因此将其称为虚拟的，而持续被激发的电子数则称为真实的。虚拟电荷载流子最近与高次谐波产生和瞬态吸收相关联，但光电流的产生可能源于真实的以及虚拟的电荷载流子。然而，目前尚缺少载流子类型的产生与其对具有技术相关性的可观测物的重要性之间的联系。在这里，我们表明，使用少周期激光脉冲，可以在金-石墨烯-金异质结构的光电流产生过程中激发并区分真实和虚拟电荷载流子。根据用于光激发的波形，真实载流子获得净动量并传播到金电极，而虚拟载流子则在金-石墨烯界面产生可读出的极化响应。基于这些见解，我们进一步展示了用于未来光波电子学的逻辑门的概念验证。我们的结果提供了一种直接的方法来监测和激发真实和虚拟电荷载流子。对每种类型载流子的单独控制将显著增加集成电路的设计空间，并使太赫兹信号处理更接近现实。
