18 research outputs found
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
A tunable topological insulator in the spin helical Dirac transport regime
Helical Dirac fermions—charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum—are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose– Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently
been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators—materials with a bulk insulating gap of spin–orbit origin and surface states protected against scattering by time-reversal symmetry—and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuthbased class of material by combining spin-imaging and
momentum-resolved spectroscopies, bulk charge compensation,
Hall transport measurements and surface quantum control. Our
results reveal a spin-momentum locked Dirac cone carrying a nontrivial
Berry’s phase that is nearly 100 per cent spin-polarized,
which exhibits a tunable topological fermion density in the vicinity
of the Kramers point and can be driven to the long-sought
topological spin transport regime. The observed topological nodal
state is shown to be protected even up to 300 K. Our demonstration
of room-temperature topological order and non-trivial spintexture
in stoichiometric Bi_2Se_3.M_x (M_x indicates surface doping
or gating control) paves the way for future graphene-like studies of
topological insulators, and applications of the observed spinpolarized
edge channels in spintronic and computing technologies
possibly at room temperature
A new myxosporean species Myxobolus sclerii sp. nov. and one known species M. stomum Ali et al. 2003 from two Indian major carp fishes
The present communication deals with description of one new species of Myxobolus (Myxozoa: Myxosporea: Bivalvulida), M. sclerii sp. nov. infecting eye ball of Catla catla (Hamilton) and redescription of M. stomum infecting scales of Labeo rohita (Hamilton), two major carps of Kanjali and Ropar Wetlands respectively. Spores of M. sclerii sp. nov. measure 7.9–9.5(8.7 ± 1.13) × 4.3–5.7(5 ± 0.98) μm in size. Parietal folds absent. Polar capsules two, equal and measuring 4–5.4(4.7 ± 0.98) × 1–2.6(1.8 ± 1.31) μm in size. A rod-shaped medium-sized intercapsular process is present. Iodinophilous vacuole present measuring 2.19–4.13(3.16 ± 1.37) μm in diameter. Spores of M. stomum Ali et al.2003 measure 9.8–10.3(10.0 ± 0.35) × 7.9–8.7(8.3 ± 0.56) μm in size, with rounded anterior and posterior end. Spore valves smooth, symmetrical, thick measuring 0.88 μm in thickness. Parietal folds absent. Two anteriorly situated polar capsules are equal, pear-shaped measuring 4.8–5.2(5.0 ± 0.28) × 1.5–2.3(1.9 ± 0.56) μm in size, each with a neck leading to a fine duct opening independently. Both polar capsules converge slightly anteriorly but diverge apart posteriorly occupying more than half of spore body. Intercapsular appendix is absent. Earlier, the parasite was recorded in the buccal cavity, muscles and lips of Plectorhynchus gaterinus (Forsskal), Egypt. A new locality-Ropar Wetland, a new location-scales and a new host- Labeo rohita (Hamilton) are recorded for this parasite
Two new species of Myxobolus (Myxozoa:Myxosporea:Bivalvulida) from freshwater fishes of Punjab wetlands (India)
During the present study two new species were collected from mucous membrane around gill lamellae of Puntius sophore (Ham.) vern. chittal and Cirrhina mrigala (Ham.) vern. mrigal from Harike Wetland, Punjab respectively. Spore of the first species i.e. Myxobolus chittalii are histozoic, pear shaped with characteristic nipple-like anterior end and rounded posterior end. They measure 9.0 × 6.18 μm. Polar capsules are two, equal, measuring 4.5 × 2.4 μm, pyriform with bluntly pointed anterior end and rounded posterior end. They are placed posteriorly from the tip of the spore and are parallel to each other in the spore body cavity. A prominent, tongue shaped intercapsular process is present. Spores of the second species i.e. M. mehlhorni are histozoic, oval to egg in shape having narrow, blunt anterior end and broad rounded posterior end, measure 8.9 × 6.8 μm. Shell valves smooth, symmetrically thin, measure 0.5 μm in thickness. Parietal folds are absent. Polar capsules two, prominently unequal, placed anteriorly and converge towards the anterior end. Both polar capsules are flask-shaped with anterior end having a prominent neck. The larger polar capsule measure 3.7 × 2.5 μm occupying less than half while the smaller one measure 2.6 × 1.5 μm and occupy less than one-third of the spore body cavity. An intercapsular process is absent