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Register a new userDirac Fermion Quantum Hall Antidot in Graphene
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The ability to localize and manipulate individual quasiparticles in mesoscopic structures is critical in experimental studies of quantum mechanics and thermodynamics, and in potential quantum information devices, e.g., for topological schemes of quantum computation. In strong magnetic field, the quantum Hall edge modes can be confined around the circumference of a small antidot, forming discrete energy levels that have a unique ability to localize fractionally charged quasiparticles. Here, we demonstrate a Dirac fermion quantum Hall antidot in graphene in the integer quantum Hall regime, where charge transport characteristics can be adjusted through the coupling strength between the contacts and the antidot, from Coulomb blockade dominated tunneling under weak coupling to the effectively non-interacting resonant tunneling under strong coupling. Both regimes are characterized by single -flux and -charge oscillations in conductance persisting up to temperatures over 2 orders of magnitude higher than previous reports in other material systems. Such graphene quantum Hall antidots may serve as a promising platform for building and studying novel quantum circuits for quantum simulation and computation.
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We study the influences of antidot-induced bound states on transport properties of two- dimensional quantum spin Hall insulators. The bound statesare found able to induce quantum percolation in the originally insulating bulk. At some critical antidot densities, the quantum spin Hall phase can be completely destroyed due to the maximum quantum percolation. For systems with periodic boundaries, the maximum quantum percolationbetween the bound states creates intermediate extended states in the bulk which is originally gapped and insulating. The antidot in- duced bound states plays the same role as the magnetic field inthe quantum Hall effect, both makes electrons go into cyclotron motions. We also draw an analogy between the quantum percolation phenomena in this system and that in the network models of quantum Hall effect.
Three dimensionally curved graphene with a wide range of curvature radii from 25 nm to 1000 nm demonstrates that nano-scale curvature is a new degree of freedom to tune the transport properties of graphene by manipulating 2D electron kinetics on 3D curved surfaces.
Graphene samples can have a very high carrier mobility if influences from the substrate and the environment are minimized. Embedding a graphene sheet into a heterostructure with hexagonal boron nitride (hBN) on both sides was shown to be a particularly efficient way of achieving a high bulk mobility. Nanopatterning graphene can add extra damage and drastically reduce sample mobility by edge disorder. Preparing etched graphene nanostructures on top of an hBN substrate instead of SiO2 is no remedy, as transport characteristics are still dominated by edge roughness. Here we show that etching fully encapsulated graphene on the nanoscale is more gentle and the high mobility can be preserved. To this end, we prepared graphene antidot lattices where we observe magnetotransport features stemming from ballistic transport. Due to the short lattice period in our samples we can also explore the boundary between the classical and the quantum transport regime.
We numerically study the interplay of band structure, topological invariant and disorder effect in two-dimensional electron system of graphene in a magnetic field. Two emph{distinct} quantum Hall effect (QHE) regimes exist in the energy band with the unconventional half-integer QHE appearing near the band center, consistent with the experimental observation. The latter is more robust against disorder scattering than the conventional QHE states near the band edges. The phase diagram for the unconventional QHE is obtained where the destruction of the Hall plateaus at strong disorder is through the float-up of extended levels toward band center and higher plateaus always disappear first. We further predict a new insulating phase between $ u =pm 2$ QHE states at the band center, which may explain the experimentally observed resistance discontinuity near zero gate voltage.
Epitaxial graphene films have been formed on the C-face of semi-insulating 4H-SiC substrates by a high temperature sublimation process. Nano-scale square antidot arrays have been fabricated on these graphene films. At low temperatures, magneto-conductance in these films exhibits pronounced Aharonov-Bohm oscillations with the period corresponding to magnetic flux quanta added to the area of a single antidot. At low fields, weak localization is observed and its visibility is enhanced by intravalley scattering on antidot edges. At high fields, we observe two distinctive minima in magnetoconductance which can be attributed to commensurability oscillations between classical cyclotron orbits and antidot array. All mesoscopic features, surviving up to 70 K, reveal the unique electronic properties of graphene.
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