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The term “metamaterials” refers to engineered structures that interact with electromagnetic fields in an unusual but controllable way that cannot be observed with natural materials. Metamaterial design at optical frequencies oftentimes makes of controllable plasmonic interactions. Light can excite collective oscillations of conduction band electrons on a metallic nanostructure. These oscillations result in localized surface plasmon modes which can provide high confinement of fields at metal-dielectric interfaces at nanoscale. Additionally scattering and absorption characteristics of plasmon modes can be controlled by geometrical features of the metallic nanostructures. This ease of controllability has lead to the development of new concepts in light manipulation and enhancement of light-material interactions. Fano resonance and plasmonic induced transparency (PIT) are among the most promising of those. The interference between different plasmon modes induced on nanostructures generates PIT/Fano resonance at optical frequencies. The unusual dispersion characteristics observed within the PIT window can be used for designing optical metamaterials to be used in various applications including bio-chemical sensing, slow light, modulation, perfect absorption, and all-optical switching. This thesis focuses on design of novel plasmonic devices to be used in these applications. The fundamental idea behind these designs is the generation of higher-order plasmon modes, which leads to PIT/Fano resonance-like output characteristics. These are then exploited together with dynamic tunability supported by graphene and field enhancement provided by nonlinear materials to prototype novel plasmonic devices. More specifically, this thesis proposes the following plasmonic device designs. I. Nano-disk Fano resonator: Open disk-like plasmonic nanostructures are preferred for bio-chemical sensing because of their higher capacity to be in contact with greater volumes of analyte. High effective refractive index required by sensing applications is achieved though the dispersion characteristics within PIT window. Higher order modes required for Fano resonance are generated through geometrical symmetry breaking by embedding a shifted and elongated cavity into a circular disk. The resulting dual band PIT can be geometrically tuned by varying the cavity's width and rotation angle. II. Tunable Terahertz Fano resonator: The possibility to dynamically tune graphene's conductivity has made it an attractive choice over conventional noble metals to generate surface plasmon modes at Terahertz frequencies. Subsequently, a polarization-independent and dynamically tunable hybrid gold-graphene structure is designed to achieve PIT/Fano resonance by allowing graphene and metallic plasmon modes to interfere. The effective group index of the resulting resonator is found to be very high (ng=1400, several times higher than all previously reported PIT devices) within the PIT window. Dynamic tunability achieved through a gate voltage applied to graphene suggests applications in switching. III. Tunable Terahertz Fano absorber: Many photonic and optical devices rely on their ability to efficiently absorb an incoming electromagnetic field. The absorption in atomically thin graphene sheet is already very high i.e., “2.3%” per layer. However, considering its atomic thickness graphene sheet remains practically transparent to Terahertz waves. The proposed absorber design makes of an asymmetrically patterned graphene layer that supports higher order plasmon modes at Terahertz frequencies. Several of these patterned layers backed by dielectric substrates are stacked on top of each other followed by reflector screen. The dynamically controllable resonances from each graphene layer and the spacing between them are fine tuned to achieve a large bandwidth of 6.9 Terahertz (from 4.7 to 11.6 Terahertz) for over 90% absorption, which is significantly higher than that of existing metallic/graphene absorbers. IV. Three state all-optical switch: The plasmonic resonances are extremely sensitive to dielectric properties of the surrounding medium. A slight change in the dielectric constant near the metal surface results in a significant change in the plasmonic resonance. This sensitivity is enhanced in the presence of a nonlinear change in the dielectric constant. To make use of this effect, Fano resonator is used in conjunction with a Kerr nonlinear material. The resulting resonator exploits multiple (higher order) surface plasmons to generate a multi-band tri-stable response in its output. This cannot be obtained using existing nonlinear plasmonic devices that make use of single mode Lorentzian resonances. Multi-band three-state optical switching that can be realized using the proposed resonator has potential applications in optical communications and computing.

We present a theoretical analysis of surface-plasmon-mediated mode-coupling in a planar thin film metal/insulator stack. The spatial overlap of a surface plasmon polariton (SPP) and a waveguide mode results in a Fano interference analog. Tuning of the material parameters effects the modes and output fields of the system. Lastly, the intensity and phase sensitivity of the system are compared to a standard surface plasmon resonance (SPR). We begin with background information on Fano interference, an interference effect between two indistinguishable pathways. Originally described for autoionization, we discuss the analogs in other systems. We discuss the features of Fano interference in the mode diagrams, and the Fano resonance observed in the output field. The idea of a geometric Fano resonance (GFR) occurring in the angular domain is presented. Background information on surface plasmon polaritons is covered next. The dielectric properties of metals and how they relate to surface plasmons is first reviewed. The theoretical background of SPPs on an infinite planar surface is covered. The modes of a two planar interface metal/insulator stack are reviewed and the leaky properties of the waveguide are shown in the reflectance. We solve for modes of a three interface metal/insulator stack and shows an avoided crossing in the modes indicative of Fano interference. We observe the asymmetric Fano resonance in the angular domain in the reflectance. The tunability of the material parameters tunes the GFR of the system. The GFR tuning is explored and different Fano lineshapes are observed. We also observe a reversal of the asymmetry Fano lineshape, attributed to the relate phase interactions of the non-interacting modes. The phase of the GFR is calculated and discussed for the variations of the parameters. The reflected field is explored as the insulator permittivities are varied. As the waveguide permittivity is varied, we show there is little response from the system. As the exterior permittivity is varied, the reflectance exhibits the geometric Fano resonance and the tunability of the lineshape is explored. Finally, we calculate the sensitivities of our metal/insulator stack to changes in the permittivity and compare them to the sensitivities of SPRs.

Manipulating electromagnetic fields with plasmonic nanostructures has attracted researchers from interdisciplinary areas and opened up a wide variety of applications. Despite the intriguing aspect of inducing unusual optical properties such as negative indices and indefinite permittivity and permeability, engineered plasmonic nanostructures are also capable of concentrating electromagnetic waves into a diffraction-unlimited volume, thus induce incredible light-matter interaction. In this dissertation, I’ll discuss about a class of plasmonic structures that exhibit the Fano resonance. The Fano resonance is in principle the interference between two resonant modes of distinct lifetimes. Through the Fano resonance, the electromagnetic energy can be trapped in the so called “dark” mode and induce strong local field enhancement. A variety of Fano resonant nanostructures ranging from periodic planar arrays to simple clusters composed of only two particles are demonstrated in this dissertation. By artificially designing the dimensions of the structures, these Fano-resonant materials can be operated over a broad frequency range (from visible to mid-IR) to target the specific applications of interest. In this dissertation, I’ll show the following research results obtained during my PhD study: (1) the double-continuum Fano resonant materials that can slow down the speed of light over a broad frequency range with little group velocity dispersion. (2) Ultra-sensitive detection and characterization of proteins using the strong light-matter interaction provided by the Fano-reonant asymmetric metamaterials. (3) Metamaterials absorbers with nearly 100 % absorbance, tunable spectral position, expandable bandwidth, and wide angle absorption. These Fano-resonant materials can have profound influences in the areas of optical signal processing, life science, bio-defense, energy harvesting and so on. / text

We demonstrate the existence of tunable bound-states in continuum (BIC) in a 1-dimensional quantum wire with two impurities by an intense monochromatic radiation field. We found that there is a new type of BIC due to the Fano interference between two optical transition channels, in addition to the ordinary BIC due to a geometrical interference between electron wave functions emitted by impurities. In both cases the BIC can be achieved by tuning the frequency of the radiation field. / text

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Neste trabalho estudamos a forma de linha na absorção de dois fotons nas transições 4f7 de defeitos cristalinos superpostas com bandas de absorção multifonons. Escrevemos o perfil de linha sob a forma de Fano. O íon em estudo é Eu++ como defeito em um cristal de CaF2. Apresentamos o desenvolvimento da instrumentação necessária para realização do experimento, e obtemos resultados de ótima qualidade. / In this work we study the absorption of two photons in the electronic transition within the 4f 7configuration wich is superposed to the vibronic structure of 4f 7 - 4f65d transition. We describe the line shape with the Fano\'s formalism. The study was carried out on Eu+2 doped CaF2. The experimental apparatus was build and the results obtained are in good agreement with the theoretical predictions.

Orientador: Antonio Carlos Ferreira Seridonio / Resumo: Esta tese é dedicada ao estudo teórico das propriedades de transp orte eletrônico do grafeno hosp edando um par de átomos adsorvidos em diferentes geometrias. Na primeira delas, verificamos a densidade lo cal de estados (LDOS) do plano de grafeno hos p edando um par de átomos adsorvidos, distantes entre si, no centro de uma célula hexagonal da rede. Nesta primeira configuração, efeitos de correlação revelaram uma es trutura multiníveis na LDOS e padrõ es de batimentos na densidade de estados (DOS) induzida. Amb os efeitos são anisotrópicos e o correm na vizinhança dos p ontos de Dirac. Em um segundo arranjo, estudamos a formação de estados ligados ao contínuo (BICs) adsorvendo um par de átomos em lados op ostos do plano de grafeno e colineares com o centro de uma célula hexagonal. Mostramos que nesta configuração a LDOS é caracterizada p or uma dep endência cúbica na energia e que um mecanismo de interferência Fano destrutiva assistida p or uma correlação de Coulomb nas impurezas leva a formação de BICs. Na terceira geometria, analisamos os efeitos do acoplamento não-lo cal de um par de átomos adsorvidos colineares a um átomo de carb ono da rede na LDOS do grafeno. Em tal arranjo, canais de tunelamento eletrônico distintos dão origem a um fator de interferência Fano q0, que se torna um parâmetro de controle natural do sistema. Verificamos três regimes distintos para o sistema: (i) quando q0 < qc1 (ponto crítico) uma dependência mista do pseudogap, ∆ ∝ | ε| , | ε| 2, leva o si... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this thesis we present a detailed theoretical study of the electronic transp ort prop erties of graphene systems hosting a pair of adatoms in distinct geometries. In the first one, where the adatoms are placed distant from each other at the center of the hexagonal cell, we verify multilevels struture in the lo cal density of states (LDOS) and b eat patterns in the induced density of states (DOS) profiles due to correlation effects. The b oth findings are anissotropic and o ccour near the Dirac p oint. In the second system, we study the formation of b ound states in the continuum (BICs) in a pair of adatoms on opp osite sides of the graphene sheet and colinear with the center of the hexagonal cell. In such a set, we show that the LDOS is caracterized by a cubic dep endence in energy and that the Fano destrutive interference assisted by Coulomb correlation in the adatoms gives rise to the BICs formation. In the third configuration, we analyze the effects of the nonlo cal coupling in a pair of adatoms collinear to a carb on atom of the graphene sheet. In such a geometry, distinct tunneling paths lead to a Fano factor of interferance q0, which becomes a natural control parameter of the system. In this sense, we verify three distinct regimes: (i) when q0 < qc1 (critical point) a mixed dependence of the pseudogap, ∆ ∝ | ε| , | ε| 2, gives rise to a phase presenting spin-degenerates BICs; (ii) near to q0 = qc1, we find a pseudogap ∆ ∝ | ε| 2 , where the system is drives to a quan... (Complete abstract click electronic access below) / Doutor

Orientador: Antonio Carlos Ferreira Seridonio / Resumo: O físico italiano Ettore Majorana propôs, no campo da Física de altas energias, a existência de férmions peculiares que têm como característica serem suas próprias antipartículas. No contexto de Física da matéria condensada, tais férmions emergem como quasipartículas de Majorana (MQPs). Da perspectiva da compu- tação quântica, duas MQPs podem compor um férmion regular e atuar como um qubit protegido, que está desacoplado do ambiente e livre do efeito de decoerência. Até onde sabemos, a verificação experimental de uma MQP ainda é questionável, apesar de alguns resultados experimentais, e desta forma, o objetivo desta tese é de propor formas experimentais a fim de ajudar na busca das assinaturas de tais excitações. Como o efeito Fano é um efeito de interferência na qual canais de tunelamento competem entre si pelo transporte eletrônico, ele torna-se uma forma de capturar tais assinaturas das MQPs em sistemas de matéria condensada. Baseado nisto, a ideia é investigar teoricamente três diferentes interferômetros a fim de obter uma assinatura definitiva das MQPs. O primeiro é um interferômetro do tipo Aharanov-Bohm composto por dois quantum dots, sendo um deles acoplado a uma MQP, que se localiza na borda de um fio de Kitaev semi-infinito na fase topológica. Ajustando o nível de Fermi dos terminais e o detuning simétrico dos níveis dos dots, mostrou-se que regimes Fano opostos resultam em uma transmitância caracterizada por distintas regiões condutoras e isolantes, que são marcas ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The Italian physicist Ettore Majorana proposed in the field of high-energy Physics the existence of peculiar fermions that constitute their own antiparticles. In the context of condensed matter Physics, these fermions are Majorana quasiparticles (MQPs). From the quantum computing perspective, two MQPs can compose a regular fermion acting as a protected qubit, which is indeed decoupled from the host environment and free of the decoherence effect. To the best of our knowledge, the experimental capture of a MQP up to now is still questionable despite some experimental results, then, the goal of this thesis is to propose helpful experiment manners in revealing signatures from such excitations. As the Fano effect is an interference phenomenon where tunneling paths compete for the electronic transport, it becomes a probe to catch fingerprints of MQPs lying on condensed matter systems. Based on this, the idea is to investigate theoretically three different interferometers in order to obtain a MQP smoking- gun signature. The first one was an Aharonov-Bohm-like interferometer composed by two quantum dots, being one of them coupled to a MQP, which is attached to one of the edges of a semi-infinite Kitaev wire within the topological phase. By changing the Fermi energy of the leads and the symmetric detuning of the levels for the dots, we show that opposing Fano regimes result in a transmittance characterized by distinct conducting and insulating regions, which are fingerprints of an iso... (Complete abstract click electronic access below) / Doutor

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Inserir a ficha catalográfica elaborada pela biblioteca após a normalização do seu trabalho. on 2018-01-29T18:30:28Z (GMT) / Submitted by Robyson dos Santos Machado null (robysonmachado@gmail.com) on 2018-01-30T17:28:31Z No. of bitstreams: 2 Tese_Robyson_29-01.pdf: 10773768 bytes, checksum: 30cf1a501f0e0488a4a7fd641ca89a3d (MD5) Tese_Robyson_FEIS.pdf: 11626510 bytes, checksum: 8eef9dcbe69dc8cabfa8af13f3d9241c (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-01-30T18:30:43Z (GMT) No. of bitstreams: 1 machado_rs_dr_ilha.pdf: 11541631 bytes, checksum: 95dc986f0b7db1798926b947044f32d2 (MD5) / Made available in DSpace on 2018-01-30T18:30:43Z (GMT). No. of bitstreams: 1 machado_rs_dr_ilha.pdf: 11541631 bytes, checksum: 95dc986f0b7db1798926b947044f32d2 (MD5) Previous issue date: 2017-12-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Esta tese é dedicada ao estudo teórico das propriedades de transp orte eletrônico do grafeno hosp edando um par de átomos adsorvidos em diferentes geometrias. Na primeira delas, verificamos a densidade lo cal de estados (LDOS) do plano de grafeno hos p edando um par de átomos adsorvidos, distantes entre si, no centro de uma célula hexagonal da rede. Nesta primeira configuração, efeitos de correlação revelaram uma es trutura multiníveis na LDOS e padrõ es de batimentos na densidade de estados (DOS) induzida. Amb os efeitos são anisotrópicos e o correm na vizinhança dos p ontos de Dirac. Em um segundo arranjo, estudamos a formação de estados ligados ao contínuo (BICs) adsorvendo um par de átomos em lados op ostos do plano de grafeno e colineares com o centro de uma célula hexagonal. Mostramos que nesta configuração a LDOS é caracterizada p or uma dep endência cúbica na energia e que um mecanismo de interferência Fano destrutiva assistida p or uma correlação de Coulomb nas impurezas leva a formação de BICs. Na terceira geometria, analisamos os efeitos do acoplamento não-lo cal de um par de átomos adsorvidos colineares a um átomo de carb ono da rede na LDOS do grafeno. Em tal arranjo, canais de tunelamento eletrônico distintos dão origem a um fator de interferência Fano q0, que se torna um parâmetro de controle natural do sistema. Verificamos três regimes distintos para o sistema: (i) quando q0 < qc1 (ponto crítico) uma dependência mista do pseudogap, ∆ ∝ | ε| , | ε| 2, leva o sistema a uma fase que apresenta BICs spin-degenerados; (ii) próximo à q0 = qc1 quando ∆ ∝ | ε| 2 o sistema é conduzido a uma transição de fase quântica em que a nova fase é caracterizada por BICs magnéticos, e (iii) no segundo valor crítico, q0 > qc2, a dependência cúbica do pseudogap com a energia recupera a degenerescência de spin e a fase com BICs nãomagnéticos é restaurada. Verificamos ainda que um acoplamento local, nesta mesma geometria, não é propício a formação de BICs. No último caso, examinamos a afirmação de que o grafeno livre não demonstra qualquer propriedade ferróica, e mostramos que quando hospedando um par de impurezas ele pode ser conduzido a fases ferroelétrica e multiferróica por meio de um controle da inclinação dos cones de Dirac. A transição para a fase ferroelétrica ocorre gradativamente, enquanto que a fase multiferróica anômala surge abruptamente em uma transição de fase quântica. / In this thesis we present a detailed theoretical study of the electronic transp ort prop erties of graphene systems hosting a pair of adatoms in distinct geometries. In the first one, where the adatoms are placed distant from each other at the center of the hexagonal cell, we verify multilevels struture in the lo cal density of states (LDOS) and b eat patterns in the induced density of states (DOS) profiles due to correlation effects. The b oth findings are anissotropic and o ccour near the Dirac p oint. In the second system, we study the formation of b ound states in the continuum (BICs) in a pair of adatoms on opp osite sides of the graphene sheet and colinear with the center of the hexagonal cell. In such a set, we show that the LDOS is caracterized by a cubic dep endence in energy and that the Fano destrutive interference assisted by Coulomb correlation in the adatoms gives rise to the BICs formation. In the third configuration, we analyze the effects of the nonlo cal coupling in a pair of adatoms collinear to a carb on atom of the graphene sheet. In such a geometry, distinct tunneling paths lead to a Fano factor of interferance q0, which becomes a natural control parameter of the system. In this sense, we verify three distinct regimes: (i) when q0 < qc1 (critical point) a mixed dependence of the pseudogap, ∆ ∝ | ε| , | ε| 2, gives rise to a phase presenting spin-degenerates BICs; (ii) near to q0 = qc1, we find a pseudogap ∆ ∝ | ε| 2 , where the system is drives to a quantum phase transition exhibiting magnetics BICS, and (iii) for the second critical point (q0 > qc2) the cubic dependence of the pseudogap in energy recover the spin degeneracy, thus restoring the non-magnetic BICs phase. In such geometry, we also verify that the local coupling does not allow the BICs formation. At last, we show that a graphene sheet hosting a pair of impurities can present ferroic and multiferroic phases by controling the slope of the Dirac cones. The transition to the ferroic phase occurs gradatively, while the anomalous multiferroic phase emerges abruptaly by means a quantum phase transition.