Spin polarization andg-factor enhancement in graphene nanoribbons in a magnetic field

Abstract

We provide a systematic quantitative description of spin polarization in armchair and zigzag graphene nanoribbons (GNRs) in a perpendicular magnetic field. We first address spinless electrons within the Hartree approximation, studying the evolution of the magnetoband structure and formation of the compressible strips. We discuss the potential profile and the density distribution near the edges and the difference and similarities between armchair and zigzag edges. Accounting for the Zeeman interaction and describing the spin effects via the Hubbard term, we study the spin-resolved subband structure and relate the spin polarization of the system at hand to the formation of the compressible strips for the case of spinless electrons. At high magnetic field the calculated effective g factor varies around a value of g * ≈ 2.25 for armchair GNRs and g * ≈ 3 for zigzag GNRs. An important finding is that in zigzag GNRs the zero-energy mode remains pinned to the Fermi energy and becomes fully spin polarized for all magnetic fields, which, in turn, leads to a strong spin polarization of the electron density near the zigzag edge. Because of this the effective g factor in zigzag GNRs is strongly enhanced at low fields reaching values up to g * ≈ 30. This is in contrast to armchair GNRs, where the effective g factor at low field is close to its bare value, g = 2.

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

“…This is similar to the spin polarization of compressible strips in quantum wires and graphene nanoribbons in a high magnetic field. 29,33 For the case of the (2,1) GB, the corresponding state is fully occupied even for small applied V g , and therefore the spin-up and spin-down electron densities are the same. As a result, the potential felt by different spin species is the same and the spin polarization for the (2,1) state is completely suppressed.…”

“…For the case of electrons with spin (σ = ↑,↓) we introduce spin-dependent electron densities n σ r and use the same formalism as described above with a Hubbard Hamiltonian of the form H = H ↑ + H ↓ , 29,31 …”

Gate electrostatics and quantum capacitance in ballistic graphene devices

“…Here, we probe the total effective capacitance profile ( ) tot x α across ballistic graphene nanoconstrictions ( Fig.1b) with different degrees of edge disorder in a perpendicular magnetic field via magnetoconductance measurements. It is noteworthy that the local capacitance is accessible with these measurements in graphene devices [5,6,21], similar to conventional semiconductor structures defined in 2D electron gasses [5,22]. Indeed, magnetoconductance measurements are particularly relevant for the characterization of narrow (≤ 150 nm) confined channels [22], where alternative magnetocapacitance techniques are limited due to several reasons.…”

Effect of edge reconstruction and electron-electron interactions on quantum transport in graphene nanoribbons

“…It has also been shown that electron-electron interactions modify electron conduction in GNRs substantially. 17,18 Specifically, when the electron Fermi level is not at the charge neutrality point, electrons are predicted to accumulate along the edges of the ribbon and therefore any edge imperfection may be expected to play an important role in transport. However, the interplay between this charge redistribution effect and edge reconstruction in the context of transport is yet to be examined either theoretically or experimentally.…”