Cyclotron resonance of the magnetic ratchet effect and second harmonic generation in bilayer graphene

TL;DR

This paper models the magnetic ratchet effect and second harmonic generation in bilayer graphene, revealing tunable valley currents and cyclotron resonance effects influenced by magnetic fields and inversion symmetry breaking.

Contribution

It introduces a detailed model of the magnetic ratchet effect in bilayer graphene, highlighting the role of magnetic fields and symmetry breaking in controlling current and harmonic generation.

Findings

Cyclotron resonance enhances second harmonic generation.

Valley current is large but total charge current remains zero.

Resonances at ω_c = ω and 2ω significantly boost current.

Abstract

We model the magnetic ratchet effect in bilayer graphene in which a dc electric current is produced by an ac electric field of frequency $\omega$ in the presence of a steady in-plane magnetic field and inversion-symmetry breaking. In bilayer graphene, the ratchet effect is tunable by an external metallic gate which breaks inversion symmetry. For zero in-plane magnetic field, we show that trigonal warping and inversion-symmetry breaking are able to produce a large dc valley current, but not a non-zero total dc charge current. For the magnetic ratchet in a tilted magnetic field, the perpendicular field component induces cyclotron motion with frequency $\omega_c$ and we find that the dc current displays cyclotron resonance at $\omega_c = \omega$, although this peak in the current is actually smaller than its value at $\omega_c = 0$. Second harmonic generation, however, is greatly enhanced by resonances at $\omega_c = \omega$ and $\omega_c = 2\omega$ for which the current is generally much larger than at $\omega_c = 0$.