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

Landau Levels and Edge States in Graphene with Strong Spin-Orbit Coupling

We investigate the electronic properties of graphene in a magnetic and a strain-induced pseudo-magnetic field in the presence of strong spin-orbit interactions (SOI). For a homogeneous field we provide analytical results for the Landau level eigenstates for arbitrary intrinsic and Rashba SOI, including also the effect of a Zeeman field. We then study the edge states in a semi-infinite geometry in the absence of the Rashba term. We find that, for a critical value of the magnetic field, a quantum phase transition occurs, which separates two phases both with spin-filtered helical edge states but with opposite direction of the spin current. Finally,we discuss magnetic waveguides with inhomogeneous field profiles that allow for chiral snake orbits. Such waveguides are practically immune to disorder-induced backscattering, and the SOI provides non-trivial spin texture to these modes

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