arXiv subjects

L. Martin-Moreno

Publications and source records attributed to L. Martin-Moreno.

At least 19 recordsLinked to original sources

arXiv2025

Optical Gain Through Metallic Electro-Optical Effects

Optical gain is a critical process in today's semiconductor technology and it is most often achieved via stimulated emission. In this theoretical study, we find a resonant TE mode in biased low-symmetry two-dimensional metallic systems which may lead to optical gain in the absence of stimulated emission. We do so by first modeling the optical conductivity using Boltzmann non-equilibrium transport theory and then simulating the scattering problem using a scattered-wave formalism. Assuming that the system may possess a Berry curvature dipole (BCD) and a non-zero Magnetoelectric tensor (MET), we find that the optical conductivity has a non-trivial dependence on the direction of the applied bias, which allows for probing the TE mode. After analyzing the system with one of each of the effects, we find that the resonant TE mode is only accessible when both effects are present. Further studies are necessary to find materials with a suitably large BCD and MET, in order to realize the predictions within this study.

cond-mat.mes-hall↗

arXiv2020

Interband plasmon polaritons in magnetized charge-neutral graphene

Studying the collective excitations in charge neutral graphene (CNG) has recently attracted a great interest because of unusual mechanisms of the charge carrier dynamics. The latter can play a crucial role, for instance, for superconducting phases in the periodically strained CNG and the magic angle twisted bilayer graphene or for formation of graphene plasmon polaritons (GPPs) associated with interband transitions due to the strain-induced pseudomagnetic field. Importantly, GPP in CNG can be a tool providing new insights into various intriguing quantum phenomena in CNG via optical experiments. However, interband GPPs in CNG are barely investigated, even in the simplest configurations. Here, we show that magnetically biased single layer CNG (particularly, at zero temperature) can support interband GPPs of both transverse magnetic and transverse electric polarizations. They exist inside the narrow absorption bands originating from the electronic transitions between Landau levels and are tunable by the external magnetic field. We put our study into the context of potential near-field and far-field optical experiments, thus opening the door to the exploration of CNG for optics and nanophotonics.

physics.optics↗

arXiv2014

Anomalous Reflection Phase of Graphene Plasmons and its Influence on Resonators

The phase picked up by a graphene plasmon upon scattering by an abrupt edge is commonly assumed to be $-π$. Here, it is demonstrated that for high plasmon momenta this reflection phase is $\approx -3π/4$, virtually independent on either chemical potential, wavelength or dielectric substrate. This non-trivial phase arises from a complex excitation of highly evanescent modes close to the edge, which are required to satisfy the continuity of electric and magnetic fields. A similar result for the reflection phase is expected for other two-dimensional systems supporting highly confined plasmons (very thin metal films, topological insulators, transition polaritonic layers, etc.). The knowledge of the reflection phase, combined with the phase picked up by the plasmon upon propagation, allows the estimation of resonator properties from the dispersion relation of plasmons in the infinite monolayer.

cond-mat.mes-hall↗

arXiv2014

Reversible dynamics of single quantum emitters near metal-dielectric interfaces

Here we present a systematic study of the dynamics of a single quantum emitter near a flat metal-dielectric interface. We identify the key elements that determine the onset of reversibility in these systems by using a formalism suited for absorbing media and through an exact integration of the dynamics. Moreover, when the quantum emitter separation from the surface is small, we are able to describe the dynamics within a pseudomode description that yields analytical understanding and allows more powerful calculations.

cond-mat.mes-hall↗

arXiv2013

Analytical solution for the diffraction of an electromagnetic wave by a graphene grating

An analytical method for diffraction of a plane electromagnetic wave at periodically-modulated graphene sheet is presented. Both interface corrugation and periodical change in the optical conductivity are considered. Explicit expressions for reflection, transmission, absorption and transformation coefficients in arbitrary diffraction orders are presented. The dispersion relation and decay rates for graphene plasmons of the grating are found. Simple analytical expressions for the value of the band gap in the vicinity of the first Brillouin zone edge is derived. The optimal amplitude and wavelength, guaranteeing the best matching of the incident light with graphene plasmons are found for the conductivity grating. The analytical results are in a good agreement with first-principle numeric simulations.

cond-mat.mes-hall↗

arXiv2013

Giant Faraday rotation due to excitation of magnetoplasmons in graphene microribbons

A single graphene sheet, when subjected to a perpendicular static magnetic field provides Faraday rotation that, per atomic layer, greatly surpasses that of any other known material. This Giant Faraday rotation originates from the cyclotron resonance of massless electrons, which allows dynamical tuning through either external electrostatic or magnetostatic setting. Furthermore, the rotation direction can be controlled by changing the sign of the carriers in graphene, which can be done by means of an external electric field. However, despite these tuning possibilities, the requirement of large magnetic fields hinders application of the Faraday effect in real devices, especially for frequencies higher than few THz. In this work we demonstrate that, for a given value of the static external magnetic field, giant Faraday rotation can be achieved in arrays of graphene microribbons at frequencies much higher than the corresponding cyclotron frequency. The main feature in the magneto-optical response of graphene ribbons is not associated with the cyclotron resonance but rather with the fundamental magnetoplasmon excitation of a single ribbon. The magnetoplasmon nature of Faraday rotation in graphene ribbons opens great possibilities, as the resonance frequency can be locally selected by appropriately choosing the width of the ribbon while still preserving the tuning capability through a (smaller) external magnetic field.

cond-mat.mes-hall↗

arXiv2013

Theory of the strong coupling between quantum emitters and propagating surface plasmons

Here we present the theoretical foundation of the strong coupling phenomenon between quantum emitters and propagating surface plasmons observed in two-dimensional metal surfaces. For that purpose, we develop an ab-initio quantum framework that accounts for the coherent coupling be- tween emitters and surface plasmons and incorporates the presence of dissipation and dephasing. For both a single emitter and a disordered ensemble of emitters, our formalism is able to reveal the key physical mechanisms that explain the reported phenomenology and also to determine the physical parameters that optimize the strong coupling.

cond-mat.mes-hall↗

arXiv2012

Graphene supports the propagation of subwavelength optical solitons

We study theoretically nonlinear propagation of light in a graphene monolayer. We show that the large intrinsic nonlinearity of graphene at optical frequencies enables the formation of quasi one-dimensional self-guided beams (spatial solitons) featuring subwavelength widths at moderate electric-field peak intensities. We also demonstrate a novel class of nonlinear self-confined modes resulting from the hybridization of surface plasmon polaritons with graphene optical solitons.

physics.optics↗

arXiv2012

Analytical expressions for the Electromagnetic Dyadic Green's Function in Graphene and thin layers

An analytical general analysis of the electromagnetic Dyadic Green's Function for two-dimensional sheet (or a very thin film) is presented, with an emphasis on on the case of graphene. A modified steepest descent treatment of the fields from a point dipole given in the form of Sommerfeld integrals is performed. We sequentially derive the expressions for both out-of-plane and in-plane fields of both polarizations. It is shown that the analytical approximation provided is very precise in a wide range of distances from a point source, down to a deep subwavelength region (1/100 of wavelength). We separate the contribution from the pole, the branch point and discuss their interference. The asymptotic expressions for the fields are composed of the plasmon, Norton wave and the components corresponding to free space.

cond-mat.mes-hall↗

arXiv2012

Resonant plasmonic effects in periodic graphene antidot arrays

We show that a graphene sheet perforated with micro- or nano-size antidots have prominent absorption resonances in the microwave and terahertz regions. These resonances correspond to surface plasmons of a continuous sheet "perturbed" by a lattice. They are excited in different diffraction orders, in contrast to cavity surface plasmon modes existing in disconnected graphene structures. The resonant absorption by the antidot array can essentially exceed the absorption by a continuous graphene sheet, even for high antidot diameter-to-period aspect ratios. Surface plasmon-enhanced absorption and suppressed transmission is more efficient for higher relaxation times of the charge carriers.

cond-mat.mes-hall↗

arXiv2011

Surface plasmon enhanced absorption and suppressed transmission in periodic arrays of graphene ribbons

Resonance diffraction in the periodic array of graphene micro-ribbons is theoretically studied following a recent experiment [L. Ju et al, Nature Nanotech. 6, 630 (2011)]. Systematic studies over a wide range of parameters are presented. It is shown that a much richer resonant picture would be observable for higher relaxation times of charge carriers: more resonances appear and transmission can be totally suppressed. The comparison with the absorption cross-section of a single ribbon shows that the resonant features of the periodic array are associated with leaky plasmonic modes. The longest-wavelength resonance provides the highest visibility of the transmission dip and has the strongest spectral shift and broadening with respect to the single-ribbon resonance, due to collective effects.

cond-mat.mes-hall↗

arXiv2011

Edge and waveguide THz surface plasmon modes in graphene micro-ribbons

Surface plasmon modes supported by graphene ribbon waveguides are studied and classified. The properties of both modes with the field concentration within the ribbon area (waveguiding modes) and on the edges (edge modes) are discussed. The waveguide and edge modes are shown to be separated from each other by a gap in wavenumbers. The even-parity hybridized edge mode results to be the fundamental electromagnetic mode of the ribbon, possessing also the lowest losses. All the plasmonic modes in the ribbons have an optimum frequency, at which the absorption losses are minimum, due to competition between the plasmon confinement and the frequency dependence of absorption in graphene.

cond-mat.other↗

arXiv2011

Exploring qubit-qubit entanglement mediated by one-dimensional plasmonic nanowaveguides

We exploit the qubit-qubit coupling induced by plasmon-polariton modes in a one-dimensional nanowaveguide to obtain various two-qubit entanglement situations. Firstly, we observe three phenomena occurring when preparing the initial state of the system and leaving it freely relax: spontaneous formation of entanglement, sudden birth and revival. Then, we show that plugging a laser to each of the qubit, the system arrives to an steady state which, depending on their inter-qubit distance, can also be entangled. For this situation, we also characterize the quantum state of the system showing the entanglement-purity- diagram typical for two-qubit systems.

cond-mat.mtrl-sci↗

arXiv2011

Fields radiated by a nanoemitter in a graphene sheet

The extraordinary properties of graphene make it a very promising material for use in optoelectronics. However, this is still a nascent field, where some basic properties of the electromagnetic field in graphene must be explored. Here we report on the fields radiated by a nanoemitter lying on a graphene sheet. Our results show that this field presents a rich dependence on both frequency, distance to the source and dipole orientation. This behavior is attributed to distinct peculiarities on the density of electromagnetic states in the graphene sheet and the interaction between them. The field is mainly composed of an core region of high-intensity electromagnetic field, dominated by surface plasmons, and an outer region where the field is practically the same it would be for an emitter in vacuum. Within the core region, the intensity of the electric field is several orders of magnitude larger than what it would be in vacuum. Importantly, the size of this core region can be controlled thorough external gates, which opens up many interesting applications in, for instance, surface optics and spectroscopy. Additionally, the large coupling between nanoemitters and surface plasmons makes graphene sheets a propitious stage for quantum-optics, in which the interaction between quantum objects could be externally tailored at will.

cond-mat.mes-hall↗

arXiv2011

Oblique launching of optical surface waves by a subwavelength slit

The electromagnetic field on the metal surface launched by a subwavelength slit is analytically studied, for the case when the fundamental mode inside the slit has a wavevector component along the slit axis (conical mount). Both near-field and far-field regions are discussed, and the role of surface plasmon-polaritons and Norton waves is revealed. It is shown that the distance from the slit at which NW are more intense than surface plasmons decrease with parallel wavevector, which could help experimental studies on Norton waves. Additionally, it is found that the s-polarization component, while present for any non-zero parallel wavevector, only weakly contributes to the NWs.

cond-mat.other↗

arXiv2011

Entanglement of two qubits mediated by one-dimensional plasmonic waveguides

We investigate qubit-qubit entanglement mediated by plasmons supported by one-dimensional waveguides. We explore both the situation of spontaneous formation of entanglement from an unentangled state and the emergence of driven steady-state entanglement under continuous pumping. In both cases, we show that large values for the concurrence are attainable for qubit-qubit distances larger than the operating wavelength by using plasmonic waveguides that are currently available.

cond-mat.mes-hall↗

arXiv2010

Geometrically induced modification of surface plasmons in the optical and telecom regimes

We demonstrate that the introduction of a subwavelength periodic modulation into a metallic structure strongly modifies the guiding characteristics of the surface plasmon modes supported by the system. Moreover, it is also shown how a new type of a tightly confined surface plasmon polariton mode can be created by just milling a periodic corrugation into a metallic ridge placed on top of a metal surface.

physics.optics↗

arXiv2009

Observation of enhanced transmission for s-polarized light through a subwavelength slit

Enhanced optical transmission (EOT) through subwavelength apertures is usually obtained for p-polarized light. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. Transmission measurements are compared with a coupled mode model and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

cond-mat.mes-hall↗