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N. M. R. Peres

Publications and source records attributed to N. M. R. Peres.

At least 91 records · Page 5Linked to original sources
arXiv2016

Multiple negative differential conductance regions and inelastic phonon assisted tunneling in graphene-hBN-graphene structures

In this paper we study in detail the effect of the rotational alignment between a hexagonal boron nitride (hBN) slab and the graphene layers in the vertical current of a a graphene-hBN-graphene device. We show how for small rotational angles, the transference of momentum by the hBN crystal lattice leads to multiple peaks in the I-V curve of the device, giving origin to multiple regions displaying negative differential conductance. We also study the effect of scattering by phonons in the vertical current an see how the opening up of inelastic tunneling events allowed by spontaneous emission of optical phonons leads to sharp peaks in the second derivative of the current.

cond-mat.mes-hall↗
arXiv2016

Graphene field-effect transistor array with integrated electrolytic gates scaled to 200 mm

Ten years have passed since the beginning of graphene research. In this period we have witnessed breakthroughs both in fundamental and applied research. However, the development of graphene devices for mass production has not yet reached the same level of progress. The architecture of graphene field-effect transistors (FET) has not significantly changed, and the integration of devices at the wafer scale has generally not been sought. Currently, whenever an electrolyte-gated FET (EGFET) is used, an external, cumbersome, out-of-plane gate electrode is required. Here, an alternative architecture for graphene EGFET is presented. In this architecture, source, drain, and gate are in the same plane, eliminating the need for an external gate electrode and the use of an additional reservoir to confine the electrolyte inside the transistor active zone. This planar structure with an integrated gate allows for wafer-scale fabrication of high-performance graphene EGFETs, with carrier mobility up to 1800 cm2 V-1 s-1. As a proof-of principle, a chemical sensor was achieved. It is shown that the sensor can discriminate between saline solutions of different concentrations. The proposed architecture will facilitate the mass production of graphene sensors, materializing the potential of previous achievements in fundamental and applied graphene research.

cond-mat.mes-hall↗
arXiv2015

Active magneto-optical control of spontaneous emission in graphene

We investigate the spontaneous emission rate of a two-level quantum emitter near a graphene-coated substrate under the influence of an external magnetic field or strain induced pseudo-magnetic field. We demonstrate that the application of the magnetic field can substantially increase or decrease the decay rate. We show that a suppression as large as 99$\%$ in the Purcell factor is achieved even for moderate magnetic fields. The emitter's lifetime is a discontinuous function of $|{\bf B}|$, which is a direct consequence of the occurrence of discrete Landau levels in graphene. We demonstrate that, in the near-field regime, the magnetic field enables an unprecedented control of the decay pathways into which the photon/polariton can be emitted. Our findings strongly suggest that a magnetic field could act as an efficient agent for on-demand, active control of light-matter interactions in graphene at the quantum level.

cond-mat.mes-hall↗
arXiv2015

Electrically tunable resonant scattering in fluorinated bilayer graphene

Adatom-decorated graphene offers a promising new path towards spintronics in the ultrathin limit. We combine experiment and theory to investigate the electronic properties of dilutely fluorinated bilayer graphene, where the fluorine adatoms covalently bond to the top graphene layer. We show that fluorine adatoms give rise to resonant impurity states near the charge neutrality point of the bilayer, leading to strong scattering of charge carriers and hopping conduction inside a field-induced band gap. Remarkably, the application of an electric field across the layers is shown to tune the resonant scattering amplitude from fluorine adatoms by nearly twofold. The experimental observations are well explained by a theoretical analysis combining Boltzmann transport equations and fully quantum-mechanical methods. This paradigm can be generalized to many bilayer graphene-adatom materials, and we envision that the realization of electrically tunable resonance may be a key advantage in graphene-based spintronic devices.

cond-mat.mes-hall↗
arXiv2015

Anderson localization of light in disordered superlattices containing graphene layers

We theoretically investigate light propagation and Anderson localization in one-dimensional disordered superlattices composed of dielectric stacks with graphene sheets in between. Disorder is introduced either on graphene material parameters ({\it e.g.} Fermi energy) or on the widths of the dielectric stacks. We derive an analytic expression for the localization length $ξ$, and compare it to numerical simulations using transfer matrix technique; a very good agreement is found. We demonstrate that the presence of graphene may strongly attenuate the anomalously delocalised Breswter modes, and is at the origin of a periodic dependence of $ξ$ on frequency, in contrast to the usual asymptotic decay, $ξ\propto ω^{-2}$. By unveiling the effects of graphene on Anderson localization of light, we pave the way for new applications of graphene-based, disordered photonic devices in the THz spectral range.

cond-mat.dis-nn↗
arXiv2015

Renormalization of nanoparticle polarizability in the vicinity of a graphene-covered interface

We study the electromagnetic properties of a metamaterial consisting of polarizable (nano)particles and a single graphene sheet placed at the interface between two dielectrics. We show that the particle's polarizability is renormalized because of the electromagnetic coupling to surface plasmons supported by graphene, which results in a dispersive behavior, different for the polarizability components corresponding to the induced dipole moment, parallel and perpendicular to the graphene sheet. In particular, this effect is predicted to take place for a metallic particle whose bare polarizability in the terahertz (THz) region is practically equal to the cube of its radius (times $4π\varepsilon_0$). This opens the possibility to excite surface plasmons in graphene and enhance its absorption in the THz range by simply using a monolayer of metallic particles randomly deposited on top of it, as we show by explicit calculations.

cond-mat.mes-hall↗
arXiv2015

Electronic transport across linear defects in graphene

We investigate the low-energy electronic transport across grain boundaries in graphene ribbons and infinite flakes. Using the recursive Green's function method, we calculate the electronic transmission across different types of grain boundaries in graphene ribbons. We show results for the charge density distribution and the current flow along the ribbon. We study linear defects at various angles with the ribbon direction, as well as overlaps of two monolayer ribbon domains forming a bilayer region. For a class of extended defect lines with periodicity 3, an analytic approach is developed to study transport in infinite flakes. This class of extended grain boundaries is particularly interesting, since the $K$ and $K'$ Dirac points are superposed.

cond-mat.mes-hall↗
arXiv2015

Cloaking Resonant Scatterers and Tuning Electron Flow in Graphene

We consider resonant scatterers with large scattering cross-sections in graphene that are produced by a gated disk or a vacancy, and show that a gated ring can be engineered to produce an efficient electron cloak. We also demonstrate that this same scheme can be applied to tune the direction of electron flow. Our analysis is based on a partial-wave expansion of the electronic wave-functions in the continuum approximation, described by the Dirac equation. Using a symmetrized version of the massless Dirac equation, we derive a general condition for the cloaking of a scatterer by a potential with radial symmetry. We also perform tight-binding calculations to show that our findings are robust against the presence of disorder in the gate potential.

cond-mat.mes-hall↗
arXiv2015

Strain induced edge magnetism at zigzag edge in graphene quantum dot

We study the temperature dependent magnetic susceptibility of a strained graphene quantum dot by using the determinant quantum Monte Carlo method. Within the Hubbard model on a honeycomb lattice, our unbiased numerical results show that a relative small interaction $U$ may lead to a edge ferromagnetic like behavior in the strained graphene quantum dot, and a possible room temperature transition is suggested. Around half filling, the ferromagnetic fluctuations at the zigzag edge is strengthened both markedly by the on-site Coulomb interaction and the strain, especially in low temperature region. The resultant strongly enhanced ferromagnetic like behavior may be important for the development of many applications.

cond-mat.str-el↗
arXiv2014

Terahertz response of patterned epitaxial graphene

We study the interaction between polarized terahertz (THz) radiation and micro-structured large-area graphene in transmission geometry. In order to efficiently couple the radiation into the two-dimensional material, a lateral periodic patterning of a closed graphene sheet by intercalation doping into stripes is chosen, yielding unequal transmittance of the radiation polarized parallel and perpendicular to the stripes. Indeed, a polarization contrast up to 20% is observed. The effect even increases up to 50% when removing graphene stripes in analogy to a wire grid polarizer. The polarization dependence is analyzed in a large frequency range from < 80 GHz to 3 THz, including the plasmon-polariton resonance. The results are in excellent agreement with theoretical calculations based on the electronic energy spectrum of graphene and the electrodynamics of the patterned structure.

cond-mat.mes-hall↗
arXiv2014

Optical bistability of graphene in the terahertz range

We use an exact solution of the relaxation-time Boltzmann equation in a uniform AC electric field to describe the nonlinear optical response of graphene in the terahertz (THz). The cases of monolayer, bilayer and ABA-stacked trilayer graphene are considered, and the monolayer species is shown to be the most appropriate one to exploit the nonlinear free electron response. We find that a single layer of monolayer graphene shows an optical bistability in the THz range, within the electromagnetic power range attainable in practice. The current associated with the third harmonic generation is also computed.

cond-mat.mes-hall↗
arXiv2014

Orbital symmetry fingerprints for magnetic adatoms in graphene

In this paper, we describe the formation of local resonances in graphene in the presence of magnetic adatoms containing localized orbitals of arbitrary symmetry, corresponding to any given angular momentum state. We show that quantum interference effects which are naturally inbuilt in the honeycomb lattice in combination with the specific orbital symmetry of the localized state lead to the formation of fingerprints in differential conductance curves. In the presence of Jahn-Teller distortion effects, which lift the orbital degeneracy of the adatoms, the orbital symmetries can lead to distinctive signatures in the local density of states. We show that those effects allow scanning tunneling probes to characterize adatoms and defects in graphene.

cond-mat.mes-hall↗
arXiv2013

Scattering by linear defects in graphene: a tight-binding approach

We develop an analytical scattering formalism for computing the transmittance through periodic defect lines within the tight-binding model of graphene. We first illustrate the method with a relatively simple case, the pentagon-only defect line. Afterwards, more complex defect lines are treated, namely the zz(558) and the zz(5757) ones. The formalism developed, only uses simple tight-binding concepts, reducing the problem to matrix manipulations which can be easily worked out by any computational algebraic calculator.

cond-mat.mes-hall↗
arXiv2013

Strong light-matter interaction in systems described by a modified Dirac equation

The bulk states of some materials, such as topological insulators, are described by a modified Dirac equation. Such systems may have trivial and non-trivial phases. In this paper, we show that in the non-trivial phase a strong light-matter interaction exists in a two-dimensional system, which leads to an optical conductivity at least one order of magnitude larger than that of graphene.

cond-mat.mes-hall↗
arXiv2013

A Primer on Surface Plasmon-Polaritons in Graphene

We discuss the properties of surface plasmons-polaritons in graphene and describe three possible ways of coupling electromagnetic radiation in the terahertz (THz) spectral range to this type of surface waves. (i) the attenuated total reflection (ATR) method using a prism in the Otto configuration, (ii) graphene micro-ribbon arrays or monolayers with modulated conductivity, (iii) a metal stripe on top of the graphene layer, and (iv) graphene-based gratings. The text provides a number of original results along with their detailed derivation and discussion.

cond-mat.mes-hall↗
arXiv2012

Exact solution for square-wave grating covered with graphene: Surface plasmon-polaritons in the THz range

We provide an analytical solution to the problem of scattering of electromagnetic radiation by a square-wave grating with a flat graphene sheet on top. We show that for deep groves there is a strong plasmonic response with light absorption in the graphene sheet reaching more than 45%, due to the excitation of surface plasmon-polaritons. The case of grating with a graphene sheet presenting an induced periodic modulation of the conductivity is also discussed.

cond-mat.mes-hall↗
arXiv2012

Complete light absorption in graphene-metamaterial corrugated structures

We show that surface-plasmon polaritons excited in negative permittivity metamaterials having shallow periodic surface corrugation profiles can be explored to push the absorption of single and continuous sheets of graphene up to 100%. In the relaxation regime, the position of the plasmonic resonances of the hybrid system is determined by the plasma frequency of the metamaterial, allowing the frequency range for enhanced absorption to be set without the need of engineering graphene.

cond-mat.mes-hall↗