arXiv subjects

Mauro Cuevas

Publications and source records attributed to Mauro Cuevas.

17 recordsLinked to original sources

arXiv2026

Optical Response of Graphene Quantum Dots in the Visible Spectrum: A Combined DFT-QED Approach

We propose a model based on density functional theory (DFT) and quantum electrodynamics (QED) to study the dynamical characteristics of graphene quantum dots (GQDs). We assume the GQD edges are saturated with hydrogen atoms, effectively making it a polycyclic aromatic hydrocarbon (PAH) such as coronene. By combining the GQD spectrum calculated from a time-dependent DFT (TDDFT) with the dynamical behavior of a QD model derived from QED, we calculate the main optical characteristics of the GQD, such as its transition frequencies, the dipole moment associated to each of those transitions, life-time and the population dynamics of the molecular levels. Owing to the close match between the calculated spectrum and experimental results, our results represent a significant contribution to research on quantum treatments of light-matter interactions in realistic 2D nanomaterials.

cond-mat.mes-hall↗

arXiv2024

Surface recoil force on dielectric nano--particles enhancement via graphene acoustic surface plasmons excitation: non--local effects consideration

Controlling opto--mechanical interactions at sub--wavelength levels is of great importance in academic science and nano--particle manipulation technologies. This letter focuses on the improvement of the recoil force on nano--particles placed close to a graphene--dielectric--metal structure. The momentum conservation involving the non--symmetric excitation of acoustic surface plasmons (ASPs), via near field circularly polarized dipolar scattering, % induced by the circular dipole moment on the nano--particle, implies the occurrence of a huge momentum kick on the nano--particle. Owing to the high wave--vector values entailed in the near field scattering process, it has been necessary to consider %apply the non--locality of the graphene electrical conductivity to explore the influence of the scattering loss on this large--wave--vector region, which is neglected by the semi--classical model. Surprisingly, %our results show that %, \textcolor{red}{depending on the particle position and the dielectric thickness layer}, the contribution of ASPs to the recoil force %can be is negligibly modified when the non--local effects are incorporated through the graphene conductivity. On the contrary, our results show that the contribution of the non--local scattering loss to this force becomes dominant when the particle is placed very close to the graphene sheet and that it is mostly independent of the dielectric thickness layer. Our work can be helpful for designing new and better performing large--plasmon momentum opto--mechanical structures using scattering highly dependent of the polarization for moving dielectric nano--particles.

physics.optics↗

arXiv2022

Giant terahertz pulling force within an evanescent field propelled by wave coupling into radiation and bound modes

Manipulation of subwavelength objects by engineering the electromagnetic waves in the environment medium is pivotal for several particle handling techniques. In this letter, we theoretically demonstrate the possibility of engineering a compact and tunable plasmon-based terahertz tweezer using a graphene monolayer that is deposited on a high-index substrate. Under total-internal-reflection illumination, such device is shown to be capable of inducing an enhanced rotating polarizability thus enabling directional near-field coupling into the graphene plasmon mode and radiation modes in the substrate. As a result of the total momentum conservation, the net force exerted on the particle points in a direction opposite to the pushing force of the exciting evanescent field. Our results can contribute to novel realizations of photonic devices based on polarization dependent interactions between nanoparticles and electromagnetic mode fields.

physics.optics↗

arXiv2021

Terahertz binding of nanoparticles based on graphene surface plasmons excitations

This work studies the optical binding of a dimer composed by dielectric particles close to a graphene sheet. Using a rigorous electromagnetic method, we calculated the optical force acting on each nanoparticle. In addition, we deduced analytical expressions enabling to evaluate the contribution of graphene surface plasmons (GSPs) to optical binding. Our results show that surface plasmon on graphene excitations generate multiple equilibrium positions for which the distance between particles are tens of times smaller than the photon wavelength. Moreover, these positions can be dynamically controlled by adjusting the chemical potential on graphene. Normal and oblique incidence have been considered.

physics.optics↗

arXiv2021

Dispersion properties of plasmonic sub-wavelength elliptical wires wrapped with graphene

One fundamental motivation to know the dispersive, or frequency dependent characteristics of localized surface plasmons (LSPs) supported by elliptical shaped particles wrapped with graphene sheet, as well as their scattering characteristics when these elliptical LSPs are excited, is related with the design of plasmonic structures capable to manipulate light at sub-wavelength scale. The anisotropy imposed by the ellipse eccentricity can be used as a geometrical tool for controlling plasmonic resonances. Unlike metallic case, where the multipolar eigenmodes are independent of each other, we find that the induced current on graphene boundary couples multipolar eigenmodes with the same parity. In the long wavelength limit, a recursive relation equation for LSPs in term of the ellipse eccentricity parameter is derived and explicit solutions at lowest order are presented. In this approximation, we obtain analytical expressions for both the anisotropic polarizability tensor elements and the scattered power when LSPs are excited by plane wave incidence.

physics.optics↗

arXiv2021

Dyadic Green's function for the graphene-dielectric stack with arbitrary field and source points

In this paper, dyadic Green's function for a graphene-dielectric stack is formulated based on the scattering superposition method. To this end, scattering Green's function in each layer is expanded in terms of cylindrical vector wave functions with unknown coefficients. Using the Kronecker delta function in the field expansion, it is considered that the field and source points lie in the arbitrary layers. Afterward, recurrence relations for calculating the unknown expansion coefficients are derived by applying the impedance boundary conditions at the interface of a graphene sheet surrounded by two adjacent dielectric layers. The verification of the calculated coefficients is conducted by utilizing them in the analysis of graphene-based structures with different numbers of layers, including 1) free-standing frequency-selective surfaces (FSSs) and 2) parallel plates (PPs) with graphene walls. A potential application of our proposed structure is investigating the interaction of donor-acceptor pairs resided in the arbitrary layers of the graphene-dielectric stack with a desired number of layers.

physics.comp-ph↗

arXiv2021

Spaser and Optical Amplification Conditions in Graphene-Coated Active Wires

This work analyzes the optical properties of a localized surface plasmon (LSP) spaser made of a dielectric active wire coated with a graphene monolayer. Our theoretical results, obtained by using rigorous electromagnetic methods, illustrate the non-radiative transfer between the active medium and the localized surface plasmons of the graphene. In particular, we focus on the lasing conditions and the tunability of the LSP spaser in two cases: when the wire is made of an infrared/THz transparent dielectric material and when it is made of a metal-like material. We analyze the results by comparing them with analytical expressions obtained by us using the quasistatic approximation. We show that the studied systems present a high tunability of the spaser resonances with the geometrical parameters as well as with the chemical potential of the graphene.

physics.optics↗

arXiv2020

Lasing condition for trapped modes in subwavelength--wired PT--symmetric resonators

The ability to control the laser modes within a subwavelength resonator is of key relevance in modern optoelectronics. This work deals with the theoretical research on optical properties of a PT--symmetric nano--scaled dimer formed by two dielectric wires, one is with loss and the other with gain, wrapped with graphene sheets. We show the existence of two non--radiating trapped modes which transform into radiating modes by increasing the gain--loss parameter. Moreover, these modes reach the lasing condition for suitable values of this parameter, a fact that makes these modes to achieve an ultra high quality factor that is manifested on the response of the structure when it is excited by a plane wave. Unlike other mechanism that transform trapped modes into radiating modes, we show that the variation of gain--loss parameter in the balanced loss--gain structure here studied leads to a variation in the phase difference between induced dipole moments on each wires, without appreciable variation in the modulus of these dipole moments. We provide an approximated method that reproduces the main results provided by the rigorous calculation. Our theoretical findings reveal the possibility to develop unconventional optical devices and structures with enhanced functionality.

physics.optics↗

arXiv2019

Enhanced energy transfer via graphene-coated wire surface plasmons

This work analyzes the electromagnetic energy transfer rate between donor and acceptor quantum emitters close to a graphene-coated wire. We discuss the modification of the energy transfer rate when the emitters are interfaced via surface plasmon (SP) environments. All of the notable effects on the spatial dependence of the energy transfer are highlighted and discussed in terms of SP propagation characteristics. Our results show that a dramatically enhancement of the energy transfer occur when the graphene wire SPs are excited. Moreover, different dipole moment orientations influence differently this enhancement. As a consequence of the quasi-one-dimensional graphene wire SPs, we found that the normalized energy transfer rate reaches a maximum value at a donor-acceptor distance which is twice the value corresponding to its two-dimensional counterpart consisting of a single graphene sheet or a flat graphene waveguide. In particular, we provide a simplified model that reproduces the main features of the numerical results.

physics.optics↗

arXiv2019

Spatial modulation of the electromagnetic energy transfer by excitation of graphene waveguide surface plasmons

We theoretically study the electromagnetic energy transfer between donor and acceptor molecules near a graphene waveguide. The surface plasmons (SPs) supported by the structure provide decay channels which lead to an improvement in the energy transfer rate when the donor and acceptor are localized on the same side or even on opposite sides of the waveguide. The modification of the energy transfer rate compared to its value in absence of the waveguide are calculated by deforming the integration path into a suitable path in the complex plane. Our results show that this modification is dramatically enhanced when the symmetric and antisymmetric SPs are excited. Notable effects on the spatial dependence of the energy transfer due to the coherent interference between these SP channels, which can be tuned by chemical potential variations, are highlighted and discussed in terms of SP propagation characteristics.

physics.optics↗

arXiv2018

Theoretical investigation of the spontaneous emission on graphene plasmonic antenna in THz regime

The present work deals with a theoretical research on the emission and radiation properties of a dipole emitter source close to a dimer graphene plasmonic antenna. Modification of the radiation and the quantum efficiencies resulting from varying the position of the emitter and the orientation of its dipole moment are calculated by using a rigorous electromagnetic method based on Green's second identity. Large enhancements in the emission and the radiation of the emitter occur due to the coupling with the antenna surface plasmons in the spectral region from 4THz to 15THz. Our results show that the radiation efficiency can be enhanced by four orders of magnitude and that the quantum efficiency reaches values close to 0.8 when the emission frequency coincides with one of the resonant dipolar frequencies. On the other hand, these quantities can be reduced in a great measure at a specific frequency for a given emitter location. We present calculations of the near-field distribution and the far field intensity which reveal the role of the plasmonic antenna resonance in the emitter enhanced radiation. We show that the spectral region where the radiation is enhanced can be chosen over a wide range by varying the chemical potential of graphene from 0.2eV to 1eV.

physics.optics↗

arXiv2017

Spontaneous emission in plasmonic graphene subwavelength wires of arbitrary sections

We present a theoretical study of the spontaneous emission of a line dipole source embedded in a graphene--coated subwavelength wire of arbitrary shape. The modification of the emission and the radiation efficiencies are calculated by means of a rigorous electromagnetic method based on Green's second identity. Enhancement of these efficiencies is observed when the emission frequency coincides with one of the plasmonic resonance frequencies of the wire. The relevance of the dipole emitter position and the dipole moment orientation are evaluated. We present calculations of the near--field distribution for different frequencies which reveal the multipolar order of the plasmonic resonances.

physics.optics↗

arXiv2017

Graphene coated subwavelength wires: A theoretical investigation of emission and radiation properties

This work analyzes the emission and radiation properties of a single optical emitter embedded in a graphene-coated subwavelength wire. We discuss the modifications of the spontaneous emission rate and the radiation efficiency as a function of the position and orientation of the dipole inside the wire. Our results show that these quantities can be enhanced by several orders of magnitude when the emission frequency coincides with one of the resonance frequencies of the graphene-coated wire. In particular, high-order plasmon resonances are excited when the emitter is moved from the wire center. The modifications by varying the orientation of the dipole in the near field distribution and in the far field intensities are shown.

physics.optics↗

arXiv2017

Green formulation for studying electromagnetic scattering from graphene-coated wires of arbitrary section

We present a rigorous electromagnetic method based on Green's second identity for studying the plasmonic response of graphene-coated wires of arbitrary shape. The wire is illuminated perpendicular to its axis by a monochromatic electromagnetic wave and the wire substrate is homogeneous and isotropic. The field is expressed everywhere in terms of two unknown source functions evaluated on the graphene coating which can be obtained from the numerical solution of a coupled pair of inhomogeneous integral equations. To assess the validity of the Green formulation, the scattering and absorption efficiencies obtained numerically in the particular case of circular wires are compared with those obtained from the multipolar Mie theory. An excellent agreement is observed in this particular case, both for metallic and dielectric substrates. To explore the effects that the break of the rotational symmetry of the wire section introduces in the plasmonic features of the scattering and absorption response, the Green formulation is applied to the case of graphene-coated wires of elliptical section. As might be expected from symmetry arguments, we find a two-dimensional anisotropy in the angular optical response of the wire, particularly evident in the frequency splitting of multipolar plasmonic resonances. The comparison between the spectral position of the enhancements in the scattering and absorption efficiency spectra for low-eccentricity elliptical and circular wires allows us to guess the multipolar order of each plasmonic resonance. We present calculations of the near field distribution for different frequencies which explicitly reveal the multipolar order of the plasmonic resonances. They also confirm the previous guess and serve as a further test on the validity of the Green formulation.

physics.optics↗

arXiv2016

Surface plasmon enhancement of spontaneous emission in graphene waveguides

This work analyzes the spontaneous emission of a single emitter placed near the graphene waveguide formed by two parallel graphene monolayers, with an insulator spacer layer. In this case, the eigenmodes supported by the structure, such as surface plasmon and wave guided modes, provide decay channels for the electric dipole placed close to the waveguide. We calculated the contribution to the decay rate of symmetric and antisymmetric eigenmodes as a function of frequency and the orientation of the emitter. Our results show that the modification of the spontaneous emission due to excitation of guided modes is much lower than the corresponding decays through the excitation of symmetric and antisymmetric surface plasmons, for which, the spontaneous emission is dramatically enhanced. As a consequence of the high confinement of surface plasmons in the graphene waveguide, we found that the decay rate of the emitter with vertical orientation (with respect to graphene sheets) is twice the corresponding decay of the same emitter with parallel orientation in the whole frequency range where surface plasmon modes exist. Differently from metallo- dielectric structures, where structural parameters determine the range and magnitude of this emission, our work shows that, by dynamically tuning the chemical potential of graphene, the spectral region where the decay rate is enhanced can be chosen over a wide range.

physics.optics↗

arXiv2015

Tunable plasmonic enhancement of light scattering and absorption in graphene-coated subwavelength wires

The electromagnetic response of subwavelength wires coated with a graphene monolayer illuminated by a linearly polarized plane waves is investigated. The results show that the scattering and extintion cross-sections of the coated wire can be dramatically enhanced when the incident radiation resonantly excites localized surface plasmons. The enhancements occur for p--polarized incident waves and for excitation frequencies that correspond to complex poles in the coefficients of the multipole expansion for the scattered field. By dynamically tuning the chemical potential of graphene, the spectral position of the enhancements can be chosen over a wide range.

physics.optics↗

arXiv2015

Critical coupling layer thickness for positive or negative Goos-Hänchen shifts near the excitation of backward surface polaritons in Otto-ATR systems

A theoretical analysis of the lateral displacement (Goos-Hänchen shift) of spatially limited beams reflected from Attenuated Total Reflection (ATR) devices in the Otto configuration is presented when backward surface plasmon polaritons are excited at the interface between a positive refractive index slab and a semiinfinite metamaterial with negative refractive index. First, the stationary phase approximation and a phenomenological model based on the properties of the complex poles and zeroes of the reflection coefficient are used to demonstrate that: i) the excitation of backward surface waves can lead to both negative and positive (and not exclusively negative) Goos-Hänchen shifts, and ii) the sign of the shift depends on whether the value of the coupling layer thickness is higher or lower than a critical value characteristic of the ATR structure. Second, these findings are verified through rigorous calculations of the spatial structure of the reflected beam. For incident beams with a Gaussian profile, the lateral shift calculated as the first moment of the field distribution of the reflected beam agrees quite well with the predictions of approximate analysis. Near the resonant excitation of the backward surface plasmon polariton, large (negative or positive) Goos-Hänchen shifts are obtained, along with a splitting of the reflected beam.

physics.optics↗