Abstract
High-order terahertz (THz) sideband generation in semiconductors is a phenomenon with physics similar to that of high-order harmonic generation but in a regime of much lower frequency. Our previous paper [] found that the electron–hole pair excited by a weak optical laser can accumulate a Berry phase along a cyclic trajectory under the driving of a strong elliptically polarized THz field. Furthermore, the Berry phase appears as the Faraday rotation angle of the emission signal under short-pulse excitation in monolayer MoS. In this paper, the theory of the Berry phase in THz extreme nonlinear optics is applied to biased bilayer graphene with Bernal stacking, which has similar Bloch band features and optical properties to monolayer MoS, such as the time-reversal related valleys and the valley contrasting optical selection rule. However, the biased bilayer graphene has much larger Berry curvature than monolayer MoS, which leads to a large Berry phase of the quantum trajectory and in turn a giant Faraday rotation of the optical emission (∼1 rad for a THz field with frequency 1 THz and strength 8 kV cm−1). This surprisingly big angle shows that the Faraday rotation can be induced more efficiently by the Berry curvature in momentum space than by the magnetic field in real space. It provides opportunities to use bilayer graphene and THz lasers for ultrafast electro-optical devices.
Highlights
In semiconductors irradiated by a strong terahertz (THz) laser of frequency ω, the electron-hole pairs excited by a weak optical laser of frequency Ω are driven into large amplitude oscillations
The bilayer graphene has much larger Berry curvature than monolayer MoS2, which leads to a giant Faraday rotation of the optical emission (∼ 1 rad for a THz field with frequency 1 THz and strength 8 kV/cm)
III, we will investigate the bilayer graphene. It has about 100 times larger Berry curvature at the band edges than the monolayer MoS2 does, which leads to a giant Faraday rotation of the optical emission
Summary
In semiconductors irradiated by a strong terahertz (THz) laser of frequency ω, the electron-hole pairs excited by a weak optical laser of frequency Ω are driven into large amplitude oscillations. The quantum trajectories in semiconductors, unlike those in atoms, can be triggered by lasers on demand at designed frequencies[12] or times (relative to the THz field oscillation) This excitation at will provides a great deal of controllability and flexibility for studying the quantum trajectories in extreme nonlinear optics. The Berry curvature in bilayer graphene is much (about 100 times) larger than in monolayer MoS2 This leads to a much larger Berry phase of a quantum trajectory and in turn giant Faraday rotation. The optical response under a pulsed optical excitation is studied using the quantum trajectory theory In materials with both TR symmetry and optical selection rules, the Faraday rotation angle of the optical emission delayed by multiples of the THz period is shown to be exactly equal to the Berry phase of the stationary quantum trajectory.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
