Abstract
We investigate adiabatic quantum pumping of ballistic Dirac fermions on the surface of a strong three-dimensional topological insulator. Two different geometries are studied in detail, a normal metal–ferromagnetic–normal metal (NFN) junction and a ferromagnetic–normal metal–ferromagnetic (FNF) junction. Using a scattering matrix approach, we show that each time a new resonant mode appears in the transport window the pumped current exhibits a maximum and provide a detailed analysis of the position of these maxima. We also predict a characteristic difference between the pumped current in NFN- and FNF-junctions: whereas the former vanishes for carriers at normal incidence, the latter is finite due to the different nature of wavefunction interference in the junctions. Finally, we predict an experimentally distinguishable difference between the pumped current and the conductance.
Highlights
We investigate adiabatic quantum pumping of ballistic Dirac fermions on the surface of a strong three-dimensional topological insulator
In this paper we study quantum pumping induced by periodic modulations of gate voltages or exchange fields in two topological insulator devices: a NFN and a ferromagnetic–normal metal–ferromagnetic (FNF)-junction, see figures 1 and 2
We predict a characteristic difference between the pumped currents in the NFN- and FNF-junctions: whereas the former vanishes for carriers at normal incidence, the latter is finite due to the different nature of wavefunction interference in the junctions
Summary
Before calculating the pumped current, it is useful to first analyze the resonance conditions for reflection and transmission in the junctions. The second and more interesting condition is sin(kmd) = 0 This is the case when transmission occurs via a resonant mode of the junction and can be written as (using equations (3) and (12)): kmd. The resonant modes move from the left to the right and positive angles α (i.e. q-momenta parallel to M) begin to contribute, see figures 4(e) and (f). The behavior of the resonant modes, as shown in figures 3 and 4, forms the basis for understanding the behavior of the pumped current
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