Siarhei Ihnatsenka

Conductance quantization in strongly disordered graphene ribbons

We present numerical studies of conduction in graphene nanoribbons with different types of disorder. We find that even when defect scattering depresses the conductance to values two orders of magnitude lower than

Spin polarization of edge states and the magnetosubband structure in quantum wires

2{e}^{2}/h

Spatial spin polarization and suppression of compressible edge channels in the integer quantum Hall regime

, equally spaced conductance plateaus occur at moderately low temperatures due to enhanced electron backscattering near subband edge energies if bulk vacancies are present in the ribbon. This work accounts quantitatively for the surprising conductance quantization observed by Lin et al. [Phys. Rev. B 78, 161409(R) (2008)] in ribbons with such low conductances.

Band-gap engineering and ballistic transport in edge-corrugated graphene nanoribbons

We provide a quantitative description of the structure of edge states in split-gate quantum wires in the integer quantum Hall regime. We develop an effective numerical approach based on the Greens ...

Conductance of a quantum point contact based on spin-density-functional theory

We perform systematic numerical studies of the structure of spin-resolved compressible strips in split-gate quantum wires taking into account the exchange and correlation interactions within the density functional theory in the local spin-density approximation. We find that for realistic parameters of the wire the exchange interaction can completely suppress the formation of the compressible strips. As the depletion length or magnetic field are increased, the compressible strips starts to form first for the spin-down and then for spin-up edge channels. We demonstrate that the widths of these strips plus the spatial separation between them caused by the exchange interaction are equal to the width of the compressible strip calculated in the Hartree approximation for spinless electrons. We also discuss the effect of electron density on the suppression of the compressible strips in quantum wires.

Resonant reflection at magnetic barriers in quantum wires

We calculate the band structure and the conductance of periodic edge-corrugated graphene nanoribbons within the framework of the tight-binding p-orbital model. We consider corrugated structures based on host ribbons with armchair and zigzag edges and three different types of corrugations (armchair edges, zigzag edges, as well as a rectangular corrugation). We demonstrate that for armchair host ribbons, depending on the type of corrugation, a band gap or low-velocity minibands appear near the charge neutrality point. For higher energies the allowed Bloch state bands become separated by ministopbands. By contrast, for corrugated ribbons with the zigzag host, the corrugations introduce neither band gaps nor stopbands (except for the case of the rectangular corrugations). The conductances of finite edge-corrugated ribbons are analyzed on the basis of the corresponding band structures. For a sufficiently large number of corrugations the conductance follows the number of the corresponding propagating Bloch states and shows pronounced oscillations due to the Fabry-Perot interference within the corrugated segments. Finally we demonstrate that edge disorder strongly affects the conductances of corrugated ribbons. Our results indicate that observation of miniband formation in corrugated ribbons would require clean, edge-disorder free samples, especially for the case of the armchair host lattice.

Electron interaction, charging, and screening at grain boundaries in graphene

We present full quantum mechanical conductance calculations of a quantum point contact QPC performed in the framework of the density functional theory DFT in the local spin-density approximation LDA .W e start from a lithographical layout of the device, and the whole structure, including semi-infinitive leads, is treated on the same footing i.e., the electron-electron interaction is accounted for in both the leads and the central device region. We show that the spin degeneracy of the conductance channels is lifted and the total conductance exhibits a broad plateaulike feature at 0.52e 2 / h. The lifting of the spin degeneracy is a generic feature of all studied QPC structures both very short and very long ones, with lengths in the range 40 l500 nm. The calculated conductance also shows a hysteresis for forward and backward sweeps of the gate voltage. These features in the conductance can be traced to the formation of weakly coupled quasibound states magnetic impurities inside the QPC also predicted in previous DFT-based studies. A comparison of the results obtained with the experimental data shows, however, that while the spin-DFT-based “firstprinciples” calculations exhibit spin polarization in the QPC, the calculated conductance clearly does not reproduce the 0.7 anomaly observed in almost all QPCs of various geometries. We critically examine the major features of the standard DFT-based approach to the conductance calculations and argue that its inability to reproduce the 0.7 anomaly might be related to the infamous derivative discontinuity problem of the DFT, leading to spurious self-interaction errors not corrected in the standard LDA. Our results indicate that the formation of magnetic impurities in the QPC might be an artifact of the LDA when localization of charge is expected to occur. We thus argue that an accurate description of the QPC structure would require approaches that go beyond the standard DFT+LDA schemes.

Electron-electron interactions in antidot-based Aharonov-Bohm interferometers

The conductance of a quantum wire containing a single magnetic barrier is studied numerically by means of the recursive Greens function technique. For sufficiently strong and localized barriers, F ...

Interacting electrons in the Aharonov-Bohm interferometer

Electronic, transport, and spin properties of grain boundaries (GBs) are investigated in electrostatically doped graphene at finite electron densities within the Hartree and Hubbard approximations. ...

Magnetosubband and edge state structure in cleaved-edge overgrown quantum wires in the integer quantum Hall regime

We present a microscopic picture of quantum transport in quantum antidots in the quantum Hall regime taking electron interactions into account. We discuss the edge state structure, energy-level evolution, charge quantization and linear-response conductance as the magnetic field or gate voltage is varied. Particular attention is given to the conductance oscillations due to Aharonov-Bohm interference and their unexpected periodicity. To explain the latter, we propose the mechanisms of scattering by point defects and Coulomb blockade tunneling. They are supported by self-consistent calculations in the Hartree approximation, which indicate pinning and correlation of the single-particle states at the Fermi energy as well as charge oscillation when antidot-bound states depopulate. We have also found interesting phenomena of antiresonance reflection of the Fano type.