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Register a new userFine structure of the lowest Landau level in suspended trilayer graphene
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Magneto-transport experiments on ABC-stacked suspended trilayer graphene reveal a complete splitting of the twelve-fold degenerated lowest Landau level, and, in particular, the opening of an exchange-driven gap at the charge neutrality point. A quantitative analysis of distinctness of the quantum Hall plateaus as a function of field yields a hierarchy of the filling factors: u=6, 4, and 0 are the most pronounced, followed by u=3, and finally u=1, 2 and 5. Apart from the appearance of a u=4 state, which is probably caused by a layer asymmetry, this sequence is in agreement with Hunds rules for ABC-stacked trilayer graphene.
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We study the effect of electron-electron interaction and spin on electronic and transport properties of gated graphene nanoribbons (GNRs) in a perpendicular magnetic field in the regime of the lowest Landau level (LL). The electron-electron interaction is taken into account using the Hartree and Hubbard approximations, and the conductance of GNRs is calculated on the basis of the recursive Greens function technique within the Landauer formalism. We demonstrate that, in comparison to the one-electron picture, electron-electron interaction leads to the drastic changes in the dispersion relation and structure of propagating states in the regime of the lowest LL showing a formation of the compressible strip and opening of additional conductive channels in the middle of the ribbon. We show that the latter are very sensitive to disorder and get scattered even if the concentration of disorder is moderate. In contrast, the edge states transport is very robust and can not be suppressed even in the presence of a strong spin-flipping.
The sequence of the zeroth Landau levels (LLs) between filling factors $ u$=-6 to 6 in ABA-stacked trilayer graphene (TLG) is unknown because it depends sensitively on the non-uniform charge distribution on the three layers of ABA-stacked TLG. Using the sensitivity of quantum Hall data on the electric field and magnetic field, in an ultraclean ABA-stacked TLG sample, we quantitatively estimate the non-uniformity of the electric field and determine the sequence of the zeroth LLs. We also observe anticrossings between some LLs differing by 3 in LL index, which result from the breaking of the continuous rotational to textit{C}$_3$ symmetry by the trigonal warping.
Using transport measurements, we investigate multicomponent quantum Hall (QH) ferromagnetism in dual-gated rhombohedral trilayer graphene (r-TLG), in which the real spin, orbital pseudospin and layer pseudospins of the lowest Landau level form spontaneous ordering. We observe intermediate quantum Hall plateaus, indicating a complete lifting of the degeneracy of the zeroth Landau level (LL) in the hole-doped regime. In charge neutral r-TLG, the orbital degeneracy is broken first, and the layer degeneracy is broken last and only the in presence of an interlayer potential U. In the phase space of U and filling factor, we observe an intriguing hexagon pattern, which is accounted for by a model based on crossings between symmetry-broken LLs.
We present a fabrication process for high quality suspended and double gated trilayer graphene devices. The electrical transport measurements in these transistors reveal a high charge carrier mobility (higher than 20000 cm^2/Vs) and ballistic electric transport on a scale larger than 200nm. We report a particularly large on/off ratio of the current in ABC-stacked trilayers, up to 250 for an average electric displacement of -0.08 V/nm, compatible with an electric field induced energy gap. The high quality of these devices is also demonstrated by the appearance of quantum Hall plateaus at magnetic fields as low as 500mT.
We construct an action for the composite Dirac fermion consistent with symmetries of electrons projected to the lowest Landau level. First we construct a generalization of the $g=2$ electron that gives a smooth massless limit on any curved background. Using the symmetries of the microscopic electron theory in this massless limit we find a number of constraints on any low-energy effective theory. We find that any low-energy description must couple to a geometry which exhibits nontrivial curvature even on flat space-times. Any composite fermion must have an electric dipole moment proportional and orthogonal to the composite fermions wavevector. We construct the effective action for the composite Dirac fermion and calculate the physical stress tensor and current operators for this theory.
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