Long lived matter waves Bloch oscillations and dynamical localization by time dependent nonlinearity management

We introduce a new method to achieve long lived Bloch oscillations and dynamical localization of matter wave gap solitons in optical lattices. The method is based on time dependent modulations of the nonlinearity which can be experimentally implemented by means of the Feshbach resonance technique. In particular, we show that the width of the wave packet is preserved if time modulations of the nonlinearity are taken proportional to the curvature of the linear band spectrum which for most typical experimental settings are well approximated by harmonic time modulations of proper frequencies

Resonant excitation of confined excitons in nanocrystal quantum dots using surface plasmon-polaritons

Surface plasmon-polaritons (SPPs) in a multilayer structure consisting of a metallic film and one or more layers of nanocrystal (NC) quantum dots (QDs) are studied theoretically. It is shown that there is a resonance coupling between the plasmonpolaritons propagating along the metal/NC-layer interface and excitons confined in the dots, which produces a considerable effect on the optical properties of the structure unless the dispersion of the QD size is too large. Using a transfer matrix formalism, multilayer structures consisting of NC composite and metallic films are considered and it is demonstrated that the coupling extends over several layers constituting the structure. It can be explored in order to selectively excite QDs of different size by making a layer-by layer assembled NC planar structure and using an attenuated total reflection (ATR) configuration for the SPPenhanced excitation of the dots. In particular, it opens the possibility to control the relative intensity of light of different color, emitted by the QDs of different size.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/FIS/113199/200

Stable dark solitons in PT-symmetric dual-core waveguides

We construct dark solitons in the recently introduced model of the nonlinear dual-core coupler with the mutually balanced gain and loss applied to the two cores,which is a realization of parity-time symmetry in nonlinear optics. The main issue is stability of the dark solitons. The modulational stability of the continuous-wave background, which supports the dark solitons, is studied analytically, and the full stability is investigated in a numerical form via computation of eigenvalues for modes of small perturbations. Stability regions are thus identified in the parameter space of the system and verified in direct simulations. Collisions between stable dark solitons are briefly considered too.Fundação para a Ciência e a Tecnologia (FCT

Instabilities, solitons and rogue waves in PT-coupled nonlinear waveguides

We considered the modulational instability of continuous-wave backgrounds, and the related generation and evolution of deterministic rogue waves in the recently introduced parity–time (PT )-symmetric system of linearly coupled nonlinear Schr¨ odinger equations, which describes a Kerr-nonlinear optical coupler with mutually balanced gain and loss in its cores. Besides the linear coupling, the overlapping cores are coupled through the cross-phase-modulation term too. While the rogue waves, built according to the pattern of the Peregrine soliton, are (quite naturally) unstable, we demonstrate that the focusing cross-phase-modulation interaction results in their partial stabilization. For PT -symmetric and antisymmetric bright solitons, the stability region is found too, in an exact analytical form, and verified by means of direct simulations.Fundação para a Ciência e a Tecnologia (FCT)Binational (US–Israel) Science Foundation

Excitation of localized graphene plasmons by a metallic slit

In this paper we show that graphene surface plasmons can be excited when an electromagnetic wave packet impinges on a single metal slit covered with graphene. The excitation of the plasmons localized over the slit is revealed by characteristic peaks in the absorption spectrum. It is shown that the position of the peaks can be tuned either by the graphene doping level or by the dielectric function of the material filling the slit. The whole system forms the basis for a plasmonic sensor when the slit is filled with an analyte.The authors are grateful for useful discussions with H. Crespo. The authors acknowledge support from the European Commission through the project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. No. 881603), and the Portuguese Foundation for Science and Technology through the Strategic Funding UID/FIS/04650/2019. Additionally, the authors acknowledge financing from FEDER and the Portuguese Foundation for Science and Technology (FCT) through Project No. POCI-01-0145-FEDER-028114

Localized polariton states in a photonic crystal intercalated by a transition metal dichalcogenide monolayer

Beyond the extensively studied microcavity polaritons, which are coupled modes of semiconductor excitons and microcavity photons, nearly 2D semiconductors placed in a suitable environment can support spatially localized exciton-polariton modes. We demonstrate theoretically that two distinct types of such modes can exist in a photonic crystal with an embedded transition metal dichalcogenide (TMD) monolayer and derive an equation that determines their dispersion relations. The localized modes of two types occur in the zeroth- and first-order stop-bands of the crystal, respectively, and have substantially different properties. The latter type of the localized modes, which appear inside the light cone, can be described as a result of coupling of the TMD exciton and an optical Tamm state of the TMD-intercalated photonic crystal. We suggest an experiment for detecting these modes and simulate it numerically.Comment: 2021 Optica Publishing Group. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibite

Thresholdless surface solitons

We report on the existence of nonlinear surface waves which, on the one hand, do not require the threshold energy flow for their excitation, and, on the other hand, extend into media at both sides of the interface at low powers, i.e. can not be reduced to the conventional Tamm states. Such waves can be excited if the refractive index in at least one of the materials forming the interface is periodically modulated, with properly selected modulation depth and frequency. Thresholdless surface solitons can be stable in the entire existence domain.Comment: 3 pages, 4 figures, to appear in Optics Letter

Topological Graphene plasmons in a plasmonic realization of the Su-Schrieffer-Heeger Model

Graphene hybrids, made of thin insulators, graphene, and metals can support propagating acoustic plasmons (AGPs). The metal screening modifies the dispersion relation of usual graphene plasmons leading to slowly propagating plasmons, with record confinement of electromagnetic radiation. Here, we show that a graphene monolayer, covered by a thin dielectric material and an array of metallic nanorods, can be used as a robust platform to emulate the Su-Schrieffer-Heeger model. We calculate the Zak's phase of the different plasmonic bands to characterize their topology. The system shows bulk-edge correspondence: strongly localized interface states are generated in the domain walls separating arrays in different topological phases. We find signatures of the nontrivial phase which can directly be probed by far-field mid-IR radiation, hence allowing a direct experimental confirmation of graphene topological plasmons. The robust field enhancement, highly localized nature of the interface states, and their gate-tuned frequencies expand the capabilities of AGP-based devices.T.G.R. acknowledges funding from Fundacao para a Ciência e a Tecnologia and Instituto de Telecomunicacoes. grant number UID/50008/2020.in the framework of the project Sym-Break and Mario G. Silveirinha for useful discussions. Y.V.B., N.M.R.P. and F.H.L.K. acknowledge support from the European Commission through the project "Graphene-Driven Revolutions in ICT and Beyond" (ref. no. 881603, CORE 3). Y.V.B. and N.M.R.P. acknowledge COMPETE 2020, PORTUGAL 2020, FEDER, and the Portuguese Foundation for Science and Technology (FCT) through project POCI-010145-FEDER-028114. F.H.L.K. acknowledges financial support from the Government of Catalonia through the SGR grant, the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Programme for Centres of Excellence in RD (SEV-2015-0522), Fundacio Cellex Barcelona, Generalitat de Catalunya through the CERCA program, the Mineco grants Ramon y Cajal (RYC-201212281), Plan Nacional (FIS2013-47161-P and FIS2014-59639JIN), and the Agency for Management of University and Research Grants (AGAUR) 2017 SGR 1656. This work was supported by the ERC TOPONANOP under grant agreement n 726001 and the MINECO Plan Nacional Grant 2DNANOTOP under reference no FIS2016-81044-P

Optical conductivity of ABA stacked graphene trilayer : mid-IR resonance due to band nesting

The band structure and the optical conductivity of an ABA (Bernal-type) stacked graphene trilayer are calculated. It is shown that, under appropriate doping, a strong resonant peak develops in the optical conductivity, located at the frequency corresponding to approximately 1.4 times the interlayer hopping energy and caused by the 'nesting' of two nearly parabolic bands in the electronic spectrum. The intensity of this resonant absorption can be controlled by adjusting the gate voltage. The effect is robust with respect to increasing temperature.Financial support from the COMPETE Programme (FEDER) and the Portuguese Foundation for Science and Technology (FCT) through Projects PEst-C/FIS/UI0607/2013 and PTDC/FIS/113199/2009, as well as MATEPRO Project (ON2 Program) is gratefully acknowledged. ZR thanks the hospitality of the Physics Center of Minho University during her stay in Portugal. YVB, NMRP, RR and MIV acknowledge support by the EC under Graphene Flagship (contract no. CNECT-ICT-604391)

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 $4\pi \varepsilon _0$). 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.Financial support from the Portuguese Foundation for Science and Technology (FCT) through Projects PTDC-FIS-113199-2009 and PEst-C/FIS/UI0607/2013 is acknowledged. We also acknowledge support from the European Commission under Graphene Flagship (Contract No. CNECT-ICT-604391). J.E.S.'s work contract is financed in the framework of the Program of Recruitment of Post Doctoral Researchers for the Portuguese Scientific and Technological System, within the Operational Program Human Potential (POPH) of the QREN, participated by the European Social Fund (ESF) and national funds of the Portuguese Ministry of Education and Science (MEC)