Single-parameter quantum valley pumping in graphene with topological line defect

Abstract

Based on the Keldysh Green's function method, we report an unconventional two-parameter quantum pumping in graphene with a line defect. It is found that different from the conventional sinusoidal relation, the pumped current in this device is cosinusoid dependence on the phase difference ϕ between the two pumping potentials, which adopts its positive/nagative maximum value at ϕ = 0/π while tends to zero at ϕ = π/2. This phenomenon is related to the peculiar valley tunneling characteristics across the line defects and the exchange of valley indices on both sides of the line defect. Moreover, the pumped currents from the two valleys will flow in opposite directions along the line defect, indicating that the controllable valley current can be pumped out in the line defect without the application of strain field in graphene.

Valleytronics in two-dimensional materials with line defect

“…The latter is the opposite process. In Ren's model [96], as shown in the right panel of figure 2(c) and we will discuss later in detail, the pumped current at α ≈ −π/2 (π/2) for K ( ¢ K ) valley carriers is dominated by the photon-absorption process. However, the pumped current at smaller α is negligibly small because of the cancellation of the photon-absorption and emission processes.…”

“…The angle-dependent scattering properties of the valley states across the line defect provide possibility to separate the two valleys in the real space with the parameter electron pumping (such as the AC-field). Recently, Ren et al [96] investigated such valley separation phenomenon with singleparameter electron pumping applied across the line defect, as shown in figure 2(c). Generally, the quantum parameter pumping consists of two opposite processes, namely photon-absorption process and photon-emission process [98].…”

Robust valley filter induced by quantum constructive interference in graphene with line defect and strain

“…Liu et al [26] constructed multiple line defects to enlarge the angle range for realizing perfect valley polarization and found that the perfect valley polarization can occur even at small incident angles due to the resonant tunnelling effect. Ren et al designed the valley separation device using an AC field [27] and achieved valley polarization with a local magnetic field [28], based on the angle-dependent scattering characteristics.…”