Ultrafast valley polarization in bilayer graphene

TL;DR

This paper theoretically investigates how ultrafast circularly polarized pulses can induce and control valley polarization in bilayer graphene, with potential applications in valleytronics.

Contribution

It introduces a method to control valley polarization in bilayer graphene using ultrafast optical pulses with adjustable parameters.

Findings

Valley polarization can be tuned by the incident angle and polarization of the optical pulse.

A sequence of circular and linear pulses allows dynamic control of valley polarization.

The proposed protocol offers a platform for valleytronic applications.

Abstract

We study theoretically interaction of a bilayer graphene with a circularly polarized ultrafast optical pulse of a single oscillation at an oblique incidence. The normal component of the pulse breaks the inversion symmetry of the system and opens up a dynamical band-gap, due to which a valley-selective population of the conduction band becomes sensitive to the angle of incident of the pulse. We show that the magnitude of the valley polarization can be controlled by the angle of incidence, the amplitude, and the angle of in-plane polarization of the chiral optical pulse. Subsequently, a sequence of a circularly polarized pulse followed by a linearly polarized femtosecond-long pulse can be used to control the valley polarization created by the preceding pulse. Generally, the linearly polarized pulse depolarizes the system. The magnitude of such a depolarization depends on the amplitude, and the in-plane polarization angle of the linearly polarized pulse. Our protocol provides a favorable platform for applications in valleytronics.