Strong terahertz conductance of graphene nanoribbons under a magnetic field

Abstract

We demonstrate that the optical response of graphene nanoribbons in the terahertz to far-infrared regime can be significantly enhanced and tuned by an applied magnetic field. The dependence of the threshold frequency on the magnetic field is studied. The ribbons with the strongest terahertz conductance under a magnetic field are those with one-dimensional massless Dirac Fermion energy dispersion. For a given ribbon, there exists an optimal field under which the conductance resonance can occur at the lowest frequency.

Graphene nanoribbons in criss-crossed electric and magnetic fields

“…Second, and most important, the transition between the highest valence and lowest conduction bands become optically active owing to the acquired dispersion next to the boundaries (figure 3b). This effect is known as magnetic enhancement of the THz conductance (Liu et al 2008b). However, it does not extend much into the visible range, keeping the nanoribbons mostly transparent.…”

“…When the nanoribbon is illuminated by a linearly polarized light along the ribbon, the optical conductance can be calculated via the Kubo formula (Johnson & Dresselhaus 1973;Liu et al 2008b). For the purpose of studying the symmetry breaking in external fields, the optical field can be represented as two circularly polarized waves, yielding the optical conductance in the following form:…”

“…The corresponding effect for ANR with N = 51 is shown in figure 3a. To overcome this difficulty and make the GNRs good candidates for optoelectronic applications, such as sensors operating at low frequency, it was proposed to use strong magnetic fields (Liu et al 2008b). …”

Enhanced Optical Conductivity of Bilayer Graphene Nanoribbons in the Terahertz Regime

“…The optical conductivity of SLG and bilayer graphene has been calculated [15][16][17][18], as has the conductance of various GNRs [19]. All of this research has shown that the optical response of graphene and graphene nanoribbon is extremely weak.…”

Two-color terahertz response in bilayer graphene nanoribbons with spin-orbit coupling

“…1,2 For example, the prediction and observation of electron-hole symmetry and a half-integer quantum Hall effect, [3][4][5] finite conductivity at zero chargecarrier concentration, 3 the strong suppression of weak localization, [6][7][8] universal conductance, 9-11 magnetic enhancement of optical conductance in graphene nanoribbons, 12 and strong nonlinear response in the terahertz frequency regime. 13,14 Additional unique properties can be found in bilayer graphene ͑BLG͒.…”