Optical Control of Ultrafast Photocurrent in Graphene

TL;DR

This study demonstrates how tailored ultrafast laser pulses can control photocurrent and valley polarization in graphene, revealing mechanisms for potential applications in ultrafast photonics and quantum technologies.

Contribution

It provides a comprehensive analysis of laser-controlled photocurrent and valley polarization in graphene, highlighting the effects of laser polarization and strain engineering.

Findings

Corotating pulses generate photocurrent without valley polarization.

Counterrotating pulses induce valley polarization without photocurrent.

Strain engineering can triple photocurrent amplitude.

Abstract

The ability to manipulate electrons with the intense laser pulse enables an unprecedented control over the electronic motion on its intrinsic timescale. Present work explores the desired control of photocurrent generation in monolayer graphene on ultrafast timescale. The origin of photocurrent is attributed to the asymmetric residual electronic population in the conduction band after the end of the laser pulse, which also facilitates valley polarization. Present study offers a comprehensive analysis of the differences between these two observables, namely photocurrent and valley polarization. It is found that the corotating circularly polarized $\omega-2\omega$ laser pulses allow the generation of photocurrent but no valley polarization, whereas counterrotating circularly polarized $\omega-2\omega$ laser pulses yield significant valley polarization without any photocurrent in graphene. Different laser parameters, such as subcycle phase, wavelength, and intensity provide different knobs to control the generation of the photocurrent. In addition, threefold increase in the photocurrent's amplitude can be achieved by altering electronic properties of graphene via strain engineering. Our findings reveal intriguing underlying mechanisms into the interplay between the symmetries of the graphene's electronic structure and the driving laser pulses, shedding light on the potential for harnessing graphene's properties for novel applications in ultrafast photonics, optoelectronic devices, and quantum technologies.