163 research outputs found
Quantum finite-size effects in graphene plasmons
Get PDFGraphene plasmons are emerging as an alternative solution to noble metal plasmons, adding the advantages of tunability via electrostatic doping and long lifetimes. These excitations have been so far described using classical electrodynamics, with the carbon layer represented by a local conductivity. However, the question remains, how accurately is such a classical description representing graphene? What is the minimum size for which nonlocal and quantum finite-size effects can be ignored in the plasmons of small graphene structures? Here, we provide a clear answer to these questions by performing first-principles calculations of the optical response of doped nanostructured graphene obtained from a tight-binding model for the electronic structure and the random-phase approximation for the dielectric response. The resulting plasmon energies are in good agreement with classical local electromagnetic theory down to ~10 nm sizes, below which plasmons split into several resonances that emphasize the molecular character of the carbon structures and the quantum nature of their optical excitations. Additionally, finite-size effects produce substantial plasmon broadening compared to homogeneous graphene up to sizes well above 20 nm in nanodisks and 10 nm in nanoribbons. The atomic structure of edge terminations is shown to be critical, with zigzag edges contributing to plasmon broadening significantly more than armchair edges. This study demonstrates the ability of graphene nanostructures to host well-defined plasmons down to sizes below 10 nm, and it delineates a roadmap for understanding their main characteristics, including the role of finite size and nonlocality, thus providing a solid background for the emerging field of graphene nanoplasmonics
Stimulated light emission and inelastic scattering by a classical linear system of rotating particles
No full textThe rotational dynamics of particles subject to external illumination is found to produce light amplification and inelastic scattering at high rotation velocities. Light emission at frequencies shifted with respect to the incident light by twice the rotation frequency dominates over elastic scattering within a wide range of light and rotation frequencies. Remarkably, net amplification of the incident light is produced in this classical linear system via stimulated emission. Large optically induced acceleration rates are predicted in vacuum accompanied by moderate heating of the particle, thus supporting the possibility of observing these effects under extreme rotation conditions
Plasmon blockade in nanostructured graphene
No full textAmong the many extraordinary properties of graphene, its optical response allows one to easily tune its interaction with nearby molecules via electrostatic doping. The large confinement displayed by plasmons in graphene nanodisks makes it possible to reach the strong-coupling regime with a nearby quantum emitter, such as a quantum dot or a molecule. In this limit, the quantum emitter can introduce a significant plasmon–plasmon interaction, which gives rise to a plasmon blockade effect. This produces, in turn, strongly nonlinear absorption cross sections and modified statistics of the bosonic plasmon mode. We characterize these phenomena by studying the equal-time second-order correlation function g(2)(0), which plunges below a value of 1, thus revealing the existence of nonclassical plasmon states. The plasmon-emitter coupling, and therefore the plasmon blockade, can be efficiently controlled by tuning the doping level of the graphene nanodisks. The proposed system emerges as a new promising platform to realize quantum plasmonic devices capable of commuting optical signals at the single-photon/plasmon level
Graphene plasmon waveguiding and hybridization in individual and paired nanoribbons
Get PDFPlasmons in doped graphene exhibit relatively large confinement and long lifetime compared to noble-metal plasmons. Here, we study the propagation properties of plasmons guided along individual and interacting graphene nanoribbons. Besides their tunability via electrostatic gating, an additional handle to control these excitations is provided by the dielectric environment and the relative arrangement of the interacting waveguides. Plasmon interaction and hybridization in pairs of neighboring aligned ribbons are shown to be strong enough to produce dramatic modifications in the plasmon field profiles. We introduce a universal scaling law that considerably simplifies the analysis an understanding of these plasmons. Our work provides the building blocks to construct graphene plasmon circuits for future compact plasmon devices with potential application to optical signal processing, infrared sensing, and quantum information technology
Control of the Radiative Heat Transfer in a Pair of Rotating Nanostructures
Get PDFThe fluctuations of the electromagnetic field are at the origin of the
near-field radiative heat transfer between nanostructures, as well as the
Casimir forces and torques that they exert on each other. Here, working within
the formalism of fluctuational electrodynamics, we investigate the simultaneous
transfer of energy and angular momentum in a pair of rotating nanostructures.
We demonstrate that, due to the rotation of the nanostructures, the radiative
heat transfer between them can be increased, decreased, or even reversed with
respect to the transfer that occurs in absence of rotation, which is solely
determined by the difference in the temperature of the nanostructures. This
work unravels the unintuitive phenomena arising from the simultaneous transfer
of energy and angular momentum in pairs of rotating nanostructures.Comment: 9 pages, 4 figure
Thermal Radiation Force and Torque on Moving Nanostructures with Anisotropic Optical Response
No full text7 pages, 4 figuresNanoscale objects moving relative to a thermal radiation bath experience a drag force due to the imbalance in their interaction with the blue- and redshifted components of the electromagnetic field. Here, we show that, in addition to this drag force, moving nanostructures with an anisotropic optical response experience a lateral force and a torque that substantially modify their trajectory. These phenomena emerge from the additional coupling between the electromagnetic field components polarized parallel and perpendicular to the trajectory, enabled by the anisotropic response of the nanostructure. This work unveils the intricate dynamics of anisotropic nanostructures moving in a thermal radiation bath.The authors acknowledge support from Grant No. PID2022-137569NB-C42 funded by MICIU/AEI/10.13039/501100011033 and FEDER, EU. J. R. D-R. acknowledges support from a predoctoral fellowship from the MCIN/AEI assigned to Grant No. PID2019109502GA-I00.Peer reviewe
Chiral Lattice Resonances in 2.5-Dimensional Periodic Arrays with Achiral Unit Cells
No full text11 pags., 6 figs.Lattice resonances are collective electromagnetic modes supported by periodic arrays of metallic nanostructures. These excitations arise from the coherent multiple scattering between the elements of the array and, thanks to their collective origin, produce very strong and spectrally narrow optical responses. In recent years, there has been significant effort dedicated to characterizing the lattice resonances supported by arrays built from complex unit cells containing multiple nanostructures. Simultaneously, periodic arrays with chiral unit cells, made of either an individual nanostructure with a chiral morphology or a group of nanostructures placed in a chiral arrangement, have been shown to exhibit lattice resonances with different responses to right- and left-handed circularly polarized light. Motivated by this, here, we investigate the lattice resonances supported by square bipartite arrays in which the relative positions of the nanostructures can vary in all three spatial dimensions, effectively functioning as 2.5-dimensional arrays. We find that these systems can support lattice resonances with almost perfect chiral responses and very large quality factors, despite the achirality of the unit cell. Furthermore, we show that the chiral response of the lattice resonances originates from the constructive and destructive interference between the electric and magnetic dipoles induced in the two nanostructures of the unit cell. Our results serve to establish a theoretical framework to describe the optical response of 2.5-dimensional arrays and provide an approach to obtain chiral lattice resonances in periodic arrays with achiral unit cells.This work was sponsored by a 2022 Leonardo Grant for Researchers in Physics from the BBVA Foundation. The authors also acknowledge support from Grant No. PID2019-109502GA-I00 funded by MCIN/AEI/10.13039/501100011033 as well as the U.S. National Science Foundation (Grant No. DMR-1941680). L.Z. acknowledges support from the Department of Energy Computational Science Graduate Fellowship (Grant No. DE-SC0020347).Peer reviewe
Highly directional single-photon source
No full text8 pags., 4 figs.Single-photon emitters are a pivotal element in quantum technologies, but the generation of single photons along well-defined directions generally involves sophisticated configurations. Here, we propose a photon source capable of generating single photons with high efficiency along guided modes. Specifically, we consider a quantum emitter placed in a periodically patterned linear waveguide. The latter is designed to host a single guided mode over the spectral range of interest and display a divergence in the photonic density of states at an emission wavelength close to the period. Photons are preferentially emitted along the waveguide near that spectral region. We predict that nearly all of the emission can be made to occur along the waveguide with a reduction in the temporal uncertainty by two orders of magnitude. Our study opens a conceptually new direction in the production of single photons with a high degree of directionality and reduced temporal uncertainty.This work was supported by the European Research Council (Advanced grant 789104-eNANO),
the Spanish MCIN/AEI/10.13039/ 501100011033 (PID2020-112625GB-I00, PID2019-109502GA-I00, and Severo Ochoa CEX2019-000910-S), the Catalan CERCA Program, Fundaciós Cellex and Mir-Puig, a 2022 Leonardo Grant for Researchers in Physics (BBVA Foundation), and the U.S. National Science
Foundation (Grant No. DMR-1941680).Peer reviewe
Genome-wide transcriptomics of aging in the rotifer Brachionus manjavacas, an emerging model system
Get PDF© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in BMC Genomics 18 (2017): 217, doi:10.1186/s12864-017-3540-x.Understanding gene expression changes over lifespan in diverse animal species will lead to insights to conserved processes in the biology of aging and allow development of interventions to improve health. Rotifers are small aquatic invertebrates that have been used in aging studies for nearly 100 years and are now re-emerging as a modern model system. To provide a baseline to evaluate genetic responses to interventions that change health throughout lifespan and a framework for new hypotheses about the molecular genetic mechanisms of aging, we examined the transcriptome of an asexual female lineage of the rotifer Brachionus manjavacas at five life stages: eggs, neonates, and early-, late-, and post-reproductive adults. There are widespread shifts in gene expression over the lifespan of B. manjavacas; the largest change occurs between neonates and early reproductive adults and is characterized by down-regulation of developmental genes and up-regulation of genes involved in reproduction. The expression profile of post-reproductive adults was distinct from that of other life stages. While few genes were significantly differentially expressed in the late- to post-reproductive transition, gene set enrichment analysis revealed multiple down-regulated pathways in metabolism, maintenance and repair, and proteostasis, united by genes involved in mitochondrial function and oxidative phosphorylation. This study provides the first examination of changes in gene expression over lifespan in rotifers. We detected differential expression of many genes with human orthologs that are absent in Drosophila and C. elegans, highlighting the potential of the rotifer model in aging studies. Our findings suggest that small but coordinated changes in expression of many genes in pathways that integrate diverse functions drive the aging process. The observation of simultaneous declines in expression of genes in multiple pathways may have consequences for health and longevity not detected by single- or multi-gene knockdown in otherwise healthy animals. Investigation of subtle but genome-wide change in these pathways during aging is an important area for future study.Funding for this project was provided by R01 AG037960-01, the American Federation for Aging Research, and the Bay and Paul Foundations
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