Linear Band Structure Of Graphene Research Articles

Electron mobility in graphene without invoking the Dirac equation

The Dirac point and linear band structure in graphene bestow it with remarkable electronic and optical properties, a subject of intense ongoing research. Explanations of high electronic mobility in graphene often invoke the masslessness of electrons based on the effective relativistic Dirac-equation behavior, which are inaccessible to most undergraduate students and are not intuitive for non-physics researchers unfamiliar with relativity. Here, we show how to use only basic concepts from semiconductor theory and the linear band structure of graphene to explain its unusual effective mass and mobility, and compare them with conventional metals and semiconductors. We discuss the more intuitive concept of transverse effective mass, which emerges naturally from these basic derivations, and which approaches zero in the limit of undoped graphene at low temperature and is responsible for its extremely high mobility.

Ultrafast Broadband Charge Collection from Clean Graphene/CH3NH3PbI3 Interface.

Photocarrier generation in a material, transportation to the material surface, and collection at the electrode interface are of paramount importance in any optoelectronic and photovoltaic device. In the last collection process, ideal performance comprises ultrafast charge collection to enhance current conversion efficiency and broadband collection to enhance energy conversion efficiency. Here, for the first time, we demonstrate ultrafast broadband charge collection achieved simultaneously at the clean graphene/organic-inorganic halide perovskite interface. The clean interface is realized by directly growing perovskite on graphene surface without polymer contamination. The tunable two-color pump-probe spectroscopy, time-resolved photoluminescence spectroscopy, and time-dependent density functional theory all reveal that the clean-interfacial graphene collects band-edge photocarriers of perovskite in an ultrashort time of ∼100 fs, with a current collection efficiency close to 99%. In addition, graphene can extract deep-band hot carriers of perovskite within only ∼50 fs, several orders faster than hot carrier relaxation and cooling in perovskite itself, due to the unique Dirac linear band structure of graphene, indicating a potential high energy conversion efficiency exceeding the Shockley-Queisser limit. Adding other graphene superiority of good transparency, high carrier mobility, and extreme flexibility, clean-interfacial graphene provides an ideal charge collection layer and electrode candidate for future optoelectronic and photovoltaic applications in two dimensions.

Current relation of single energy level Graphene through considering defects and energy broadening

Graphene consist of sheet of carbon atoms bonded in sp2 manner of hexagonal lattice structure offers a number of uses in electronic application with number of desirable properties (like as large thermal conductivity, large Young’s modulus). In this paper we have modelled I-V characteristics for single energy level GNR FET (grapheme nanoribbon field effect transistor) by considering disorder in graphene sheet. Gaussian distribution function is used to show potential distribution because of this disorder at Dirac point. It is convoluted with homogeneous density of states of grapheme to get DOS for disordered graphene. Homogeneous DOS is considered for linear band structure of graphene. Then by putting this disordered DOS in defined relation I-V expression is achieved for disordered grapheme sheet. In addition energy broadening of channel (due to spilling of states from electrodes to channel and vice-versa) has been considered in this paper to get optimum result.

Review on carrier multiplication in graphene

AbstractThe remarkable gapless and linear band structure of graphene opens up new carrier relaxation channels bridging the valence and the conduction band. These Auger scattering processes change the number of charge carriers and can give rise to a significant multiplication of optically excited carriers in graphene. This is an ultrafast many‐particle phenomenon that is of great interest both for fundamental many‐particle physics as well as technological applications. Here, we review the research on carrier multiplication in graphene and Landau‐quantized graphene including theoretical modeling and experimental demonstration.Illustration of the electronic band structure of graphene including Auger scattering channels that can lead to a carrier multiplication (CM). Figure adapted from Ref. [2].

Plasmons in tunnel-coupled graphene layers: Backward waves with quantum cascade gain

Plasmons in van der Waals heterostructures comprised of graphene and related layered materials demonstrate deep subwavelength confinement and large propagation length. In this letter, we show that graphene-insulator-graphene tunnel structures can serve as plasmonic gain media. The gain stems from the stimulated electron tunneling accompanied by the emission of coherent plasmons under interlayer population inversion. The probability of tunneling with plasmon emission appears to be resonantly large at certain values of frequency and interlayer voltage corresponding to the transitions between electron states with collinear momenta - a feature unique to the linear band structure of graphene. The dispersion of plasmons undergoes a considerable transformation due to the tunneling as well, demonstrating negative group velocity in several frequency ranges.

Controllable optical negative refraction and phase conjugation in graphite thin films

Optical metamaterials have demonstrated remarkable physical properties, including cloaking, optical magnetism and negative refraction1,2,3. The last of these has attracted particular interest, mainly because of its promise for super-resolution imaging4,5,6. However, the widespread use of negative refraction at optical frequencies is challenged by high losses and strong dispersion effects, which typically limit operation to narrow frequency bands7. Here we use degenerate four-wave mixing to demonstrate controllable negative refraction at a graphite thin film, which acts as a highly efficient phase-conjugating surface. The scheme has very low loss because of the negligible thickness of the nonlinear material and it ensures broadband operation due to the linear band structure of graphene.

Infrared Spectroscopy of Tunable Dirac Terahertz Magneto-Plasmons in Graphene

We present infrared spectroscopy study of plasmon excitations in graphene in high magnetic fields. The plasmon resonance in patterned graphene disks splits into edge and bulk plasmon modes in magnetic fields. Remarkably, the edge plasmons develop increasingly longer lifetimes in high fields due to the suppression of backscattering. Moreover, due to the linear band structure of graphene, the splitting of the edge and bulk plasmon modes develops a strong doping dependence, which differs from the behavior of conventional semiconductor two-dimensional electron gas (2DEG) systems. We also observe the appearance of a higher order mode indicating an anharmonic confinement potential even in these well-defined circular disks. Our work not only opens an avenue for the investigation of the properties of Dirac magnetoplasmons but also supports the great potential of graphene for tunable terahertz magneto-optical devices.

Density functional theory based study of graphene and dielectric oxide interfaces

We study the effects of insulating oxides in their crystalline forms on the energy band structure of monolayer and bilayer graphene using a first principles density functional theory based electronic structure method and a local density approximation. We consider the dielectric oxides SiO2 (α-quartz) and Al2O3 (alumina or α-sapphire), each with two surface terminations. Our study suggests that atomic relaxations and resulting equilibrium separations play a critical role in perturbing the linear band structure of graphene in contrast to the less critical role played by dangling bonds that result from cleaving the crystal in a particular direction. For Si-terminated quartz a Dirac cone is retained while it is restored on adding a second graphene layer for O-terminated quartz. Alumina needs more than two graphene layers to preserve the Dirac cone. Our results are, at best, semi-quantitative for the common amorphous forms of the oxides considered.

Hot-electron transient and terahertz oscillations in graphene

In graphene, after the electric field is turned on, the ballistic acceleration of charge carriers up to the monochromatic optic phonon energy generates a back-and-forth motion of the whole distribution function between the zero-point energy and the phonon energy. This effect is predicted to manifest in damped terahertz oscillations of the carrier drift velocity and average energy. It only takes place within a voltage and sample length window as the direct consequence of the interplay between the electric force and the randomizing nature of deformation potential optic phonons in the linear band structure of graphene.

Graphene analogue BCN: Femtosecond nonlinear optical susceptibility and hot carrier dynamics

Third-order nonlinear absorption and refraction coefficients of a few-layer boron carbon nitride (BCN) and reduced graphene oxide (RGO) suspensions have been measured at 3.2 eV in the femtosecond regime. Optical limiting behavior is exhibited by BCN as compared to saturable absorption in RGO. Nondegenerate time-resolved differential transmissions from BCN and RGO show different relaxation times. These differences in the optical nonlinearity and carrier dynamics are discussed in the light of semiconducting electronic band structure of BCN vis-\`a-vis the Dirac linear band structure of graphene.

Velocity Renormalization and Carrier Lifetime in Graphene from the Electron-Phonon Interaction

We present a first-principles investigation of the phonon-induced electron self-energy in graphene. The energy dependence of the self-energy reflects the peculiar linear band structure of graphene and deviates substantially from the usual metallic behavior. The effective band velocity of the Dirac fermions is found to be reduced by 4%-8%, depending on doping, by the interaction with lattice vibrations. Our results are consistent with the observed linear dependence of the electronic linewidth on the binding energy in photoemission spectra.