We present experimental results of high frequency quantized charge pumping through a quantum dot formed by the electric field arising from applied voltages in a GaAs/AlGaAs system in the presence of a perpendicular magnetic field B. Clear changes are observed in the quantized current plateaus as a function of applied magnetic field. We report on the robustness in the length of the quantized plateaus and improvements in the quantization as a result of the applied B field.
We study the effect of perpendicular magnetic fields on a single-electron system with a strongly time-dependent electrostatic potential. Continuous improvements to the current quantization in these electron pumps are revealed by high-resolution measu
rements. Simulations show that the sensitivity of tunnel rates to the barrier potential is enhanced, stabilizing particular charge states. Nonadiabatic excitations are also suppressed due to a reduced sensitivity of the Fock-Darwin states to electrostatic potential. The combination of these effects leads to significantly more accurate current quantization.
The effects of electron interaction on the magnetoconductance of graphene nanoribbons (GNRs) are studied within the Hartree approximation. We find that a perpendicular magnetic field leads to a suppression instead of an expected improvement of the qu
antization. This suppression is traced back to interaction-induced modifications of the band structure leading to the formation of compressible strips in the middle of GNRs. It is also shown that the hard wall confinement combined with electron interaction generates overlaps between forward and backward propagating states, which may significantly enhance backscattering in realistic GNRs. The relation to available experiments is discussed.
We report on a study of an ultrathin topological insulator film with hybridization between the top and bottom surfaces, placed in a quantizing perpendicular magnetic field. We calculate the full Landau level spectrum of the film as a function of the
applied magnetic field and the magnitude of the hybridization matrix element, taking into account both the orbital and the Zeeman spin splitting effects of the field. For an undoped film, we find a quantum phase transition between a state with a zero Hall conductivity and a state with a quantized Hall conductivity equal to $e^2/h$, as a function of the magnitude of the applied field. The transition is driven by the competition between the Zeeman and the hybridization energies.
In a recent comment (arXiv:1607.06081), Falaye et al. claim that there are certain flaws in our publication (Phys. Rev. B, 78, 195427 (2008)). We point out that our results, in particular the analytic derivation of the energy spectrum of a circular g
raphene quantum dot exposed to a perpendicular magnetic field, are correct and equivalent to the result of Falaye et al. A misleading notation error is corrected.
We present transport measurements on a strongly coupled graphene quantum dot in a perpendicular magnetic field. The device consists of an etched single-layer graphene flake with two narrow constrictions separating a 140 nm diameter island from source
and drain graphene contacts. Lateral graphene gates are used to electrostatically tune the device. Measurements of Coulomb resonances, including constriction resonances and Coulomb diamonds prove the functionality of the graphene quantum dot with a charging energy of around 4.5 meV. We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level. Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.
S. J. Wright
,M. D. Blumenthal
,Godfrey Gumbs
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(2008)
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"Enhanced current quantization in high frequency electron pumps in a perpendicular magnetic field"
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Samuel Wright
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