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We report a novel transport regime under Anderson-localizing disorder conditions, wherein hybrid photon-plasmon quasiparticles undergo strong transmission. The effect occurs due to creation of necklace states enabled by closely-spaced eigenstates that exchange energy due to inherent non-Hermiticity.

We reveal a transition within the strong coupling regime and below the crossover to ultrastrong coupling, which alters the coupling mechanism in multimode cavities. We show that this transition drastically modifies the Hamiltonian describing the polaritons, such that different cavity modes are either entangled via the material or completely decoupled. This decoupling transition occurs due to the competition between the dissipation in the material and the finite group velocity, which governs the propagation of information across the cavity and among the molecules. The results indicate that the velocity of light, which is often not taken into account in cavity quantum electrodynamics, plays a crucial role in the formation of cavity polaritons and their dynamics.

Non-Hermiticity is known to manifest interesting modifications in the transport properties of complex systems. We report an intriguing regime of transport of hybrid quasiparticles in a non-Hermitian setting. We calculate the probability of transport, quantified by the Thouless conductance, of hybrid plasmons under varying degrees of disorder. With increasing disorder, we initially observe an expected decrease in average transmission, followed by an anomalous rise at localizing disorder. The behavior originates from the confluence of hybridization and non-Hermiticity, in which the former realizes the aggregation of eigenvalues migrating under disorder, while the latter enables energy transfer between the eigenmodes. We find that the enhanced transmission is mediated by quasiparticle hopping over various Anderson-localized states within the so-formed necklace states. We note that, in this scenario, all configurations exhibit the formation of necklace states and enhanced transport, unlike the conventionally known behavior of necklace states which only occurs in rare configurations.

We experimentally investigate a weakly disordered one-dimensional Anderson-localizing lasing system in the neighborhood of the critical disorder. This critical disorder ${\ensuremath{\delta}}_{\text{cr}}$ separates two regimes, in one of which the transport parameters show a wavelength dependence, but not in the other. We first theoretically study the temporal characteristics of lasing pulses, and extract the lifetimes of the lasing modes. The distribution of the lifetimes shows a bimodal distribution under the ${\ensuremath{\delta}}_{\text{cr}}$, which condenses into a monomodal distribution beyond the ${\ensuremath{\delta}}_{\text{cr}}$. Next, we implement an experimental scheme using a linear array of microresonators with gain, which sustains Anderson localization. Emission pulses were analyzed on a streak camera to build lifetime distributions in the experimental samples, which reproduced the theoretical predictions to a very good degree. These observations provide a direct demonstration of the effect of critical disorder on Anderson-localizing lasing systems.

Anderson localization (AL) of light[1], one of the most exotic mesoscopic phenomena, can be realized at two limits of disorder, namely, near-periodic disorder[2] or strong disorder[3]. AL can be characterized by sub-unity conductance. A critical parameter of interest is the fluctuations of conductance which reveals the statistical behaviour of the system and offers a more complete description of the underlying physics. However, the conventional technique of quantifying conductance precludes the measurement of the fluctuations thereof. In this work, we achieve Anderson localization of light in Gallium Arsenide membranes at both near-periodic disorder and strong disorder. We measure the generalized conductance fluctuations using the intensity distribution of light, and reveal hitherto unknown features of transport under the two approaches of localization.

Anderson localization is a striking phenomenon wherein transport of light is arrested due to the formation of disorder-induced resonances. Hitherto, Anderson localization has been demonstrated separately in two limits of disorder, namely, amorphous disorder and nearly-periodic disorder. However, transport properties in the two limits are yet unstudied, particularly in a statistically consistent manner. Here, we experimentally measure light transport across two-dimensional open mesoscopic structures, wherein the disorder systematically ranges from nearly-periodic to amorphous. We measure the generalized conductance, which quantifies the transport probability in the sample. Although localization was identified in both the limits, statistical measurements revealed a discrepant behavior in the generalized conductance fluctuations in the two disorder regimes. Under amorphous disorder, the generalized conductance remains below unity for any configuration of the disorder, attesting to the arrested nature of transport. Contrarily, at near-periodic disorder, the distribution of generalized conductance is heavy-tailed towards large conductance values, indicating that the overall transport is delocalized. Theoretical results from a model based on the tight-binding approximation, augmented to include open boundaries, are in excellent agreement with experiments, and also endorse the results over much larger ensembles. These results quantify the differences in the two disorder regimes, and advance the studies of disordered systems into actual consequences of Anderson localization in light transport., Comment: 27 pages, 15 figures, including Supplementary Information

Disorder-induced Anderson localization in quasiparticle transport is a challenging problem to address, even more so in the presence of dissipation as the symptoms of disorder-induced localization are very closely simulated by the absorption in a system. Following up on recent experimental studies, we numerically study the occurrence of Anderson localization in plasmonic systems at terahertz frequencies. The low losses in the material at these frequencies allow us to separately quantify the localization length and the loss length in the system. We measure a non-monotonic variation of loss length as a function of disorder, and attribute it to the participation ratio of the localized modes and resulting light occupancy in the metal. Next, we identify a unique behavior of the gap state frequencies and the density of states under disorder. We observe that the maximally displaced gap state frequencies have a propensity to remain pinned to the frequency of the gap center. Even under strong disorder, the gap does not close, and density of states profile continues to remain peaked in the gap, unlike in conventionally studied disordered systems. The origins of this behavior are traced to the nature of the quasiparticle dispersion. In our case, the quasiparticles are identified to be hybrid plasmons generated due to the hybridization of surface plasmon polaritons at a metal-dielectric interface and cavity resonances at sub-wavelength apertures thereon. This situation is akin to the Kondo systems, where dispersive conduction electrons hybridise with a localized impurity state opening a hybridization gap. Our results provide new insights on the elusive problem of the interplay of loss and localization, and underlines interesting physics at the hybridisation gap in hybrid plasmonic systems., Comment: 10 pages, 9 figures

Anderson localization lasers exploit resonant cavities formed due to structural disorder. The inherent randomness in the structure of these cavities realizes a probability distribution in all cavity parameters such as quality factors, mode volumes, mode structures etc, implying resultant statistical fluctuations in the temporal behavior. Here, we provide the first, direct experimental measurements of temporal width distributions of Anderson localization lasing pulses in intrinsically and extrinsically disordered coupled-microresonator arrays. We first illustrate signature exponential decays in the spatial intensity distributions of the lasing modes that quantify their localized character, and then measure the temporal width distributions of the pulsed emission over several configurations. We observe a hitherto-unreported dependence of temporal widths on the disorder strength, wherein the widths show a single-peaked, left-skewed distribution in extrinsic disorder and a dual-peaked distribution in intrinsic disorder. We propose a model based on coupled rate equations for an emitter and an Anderson cavity with a random mode structure, which gives excellent quantitative and qualitative agreement with the experimental observations. The experimental and theoretical analyses bring to the fore the temporal complexity in Anderson localization based lasing systems., Comment: 9 pages, 9 figures

We propose a waveguide configuration with a plasmonic grating for tailoring dispersion characteristics. The unit-cell of the plasmonic grating encompasses the subwavelength distribution of metal nanowires forming a highly resonant effective medium. The configuration enables independent control of the coupling between the plasmonic and waveguide modes via the resonant strength of the effective medium. Numerical simulations show that the line shapes of the coupled modes can be varied from Fano to electromagnetically induced transparency-like. Furthermore, we use the structure to enhance the group index from 250 to 850 and to broaden the associated band from 40 to 180 meV.

A major factor that hinders the realization of indium oxide (IO) as a potential gas/photosensor is the response time, which is quite poor. For instance, the photoresponse of dc sputtered IO films under UV and sub-bandgap illumination is known to exhibit bi-exponential decay with fast (10–100 min) and slow (∼3000 min) time constants. We demonstrate here that the response time can be greatly improved by the hot carriers generated through localized surface plasmon decay. Our study shows that when IO films are incorporated with gold nanoparticles (AuNPs), the fast and slow decay time constants are reduced by a factor of 20 and 30, respectively, at excitation wavelengths close to the localized surface plasmon resonance (LSPR) wavelength. We also show the possibility to achieve wavelength tunable reduction in the time constants by tuning the LSPR wavelength. We attribute the changes to the strong enhancement in the recombination rates facilitated by plasmon decay-mediated excess hot electrons injected into the conduction band of IO. We use a simple analytical model to explain the role of plasmon-mediated hot electrons in enhancing the recombination rate. We believe that the present results are of great significance to improve the response time of metal oxide based photodetectors/sensors, in general, since the underlying physical process depends primarily on the plasmonic nature of the AuNPs.

The plasmonic behavior of metallic nanoparticles is explicitly dependent on their shape, size and the surrounding dielectric space. This study encompasses the influence of ZnO matrix, morphology of Au nanoparticles (AuNPs) and their organization on the optical behavior of ZnO/AuNPs-ZnO/ZnO/GP structures (GP: glass plate). These structures have been grown by a multiple-step physical process, which includes dc sputtering, thermal evaporation and thermal annealing. Different analytical techniques such as scanning electron microscopy, glancing angle X-ray diffraction, Rutherford backscattering spectrometry and optical absorption have been used to study the structures. In-situ rapid thermal treatment during dc sputtering of ZnO film has been found to induce subtle changes in the morphology of AuNPs, thereby altering the profile of the plasmon band in the absorption spectra. The results have been contrasted with a recent study on the spectral response of dc magnetron sputtered ZnO films embedded with AuNPs. Initial simulation results indicate that AuNPs-ZnO/Au/GP structure reflects/absorbs UV and infrared radiations, and therefore can serve as window coatings. Copyright � 2015 American Scientific Publishers.

The size and spectral dependence of the persistent photocurrent (PPC) of dc sputtered indium oxide (IO) films has been studied under UV and sub-band gap illuminations. PPC follows bi-exponential decay with a fast and a slow process having time constants (denoted by τ f and τ s, respectively) that differ by about two orders of magnitude. τ s is associated with carrier scattering from an initial surface state to a surface or bulk state with the former dominating below a characteristic length scale of ∼60 nm. On the other hand, τ f is characterized by the process where both the initial and final states are surface related. Treating the IO film surface with tetramethyl tetraphenyl trisiloxane (TTTS) decreases τ s by a factor of 5 with τ f remaining almost unaffected, which is a clear indication of reduction of defects specific to the slow relaxation process. Based on the molecular structure and chemical activity of TTTS, it is suggested that TTTS may passivate mainly the dangling oxygen-bonds at the film surf...

In condensed matter systems, there exists a class of exotic localized electronic states wherein the localization is induced, not by a disorder or a defect, but by extremely strong interactions, for example, Kondo-insulator and Mott-insulator. In this work, we investigate and experimentally implement the photonic analog of localization induced by ultra-strong interactions in a coupled three-mode system. We show that the localization of a propagating mode can be achieved without the aid of an underlying spatial disorder, a defect, or even periodicity. We demonstrate the same by realizing ultra-strong coupling between a highly dispersive cavity plasmon mode and dimer excitons of Rhodamine B. Using a photon tunneling arrangement, we map the dispersion of the hybrid modes and provide evidence for the existence of a quasi-dispersionless hybrid mode with the sub-wavelength localization length and cavity plasmon-like characteristics.

Bergman formulation has been used to extract effective dielectric function of Au nanoparticles (AuNPs) embedded metal oxide (MO) composite thin films. The extracted composite dielectric function helps further understanding ofthe resonance features in optical far-field responses. Detailed analysis on the extracted dielectric functions point towards the possibility of using them for dispersion free optics.

A theoretical model has been adopted to simulate the effect of temperature on surface plasmon resonance (SPR) of a gold film by modeling its dielectric functions at various temperatures. A two-prism experimental arrangement that uses Kretschmann configuration in angular interrogation mode has been used to study SPR. Reflectivity measurements as a function of temperature have been performed at different positions of the resonance spectrum. Observed intensity variations reveal a considerable sensitivity of the reflectivity towards temperature which can further be utilized for extracting thermal transport properties.

Photochromic transitions in silvernanoparticles (AgNPs) embedded titanium dioxide (TiO2) films under green light illumination are marked by reduction in strength and blue shift in the position of the localized surface plasmon resonance (LSPR) associated with AgNPs. These transitions, which happen in the sub-nanometer length scale, have been analysed using the variations observed in the effective dielectric properties of the Ag-TiO2nanocompositefilms in response to the size reduction of AgNPs and subsequent changes in the surrounding medium due to photo-oxidation. Bergman-Milton formulation based on spectral density approach is used to extract dielectric properties and information about the geometrical distribution of the effective medium. Combined with finite element method simulations, we isolate the effects due to the change in average size of the nanoparticles and those due to the change in the dielectric function of the surrounding medium. By analysing the dynamics of photochromic transitions in the effective medium, we conclude that the observed blue shift in LSPR is mainly because of the change in the dielectric function of surrounding medium, while a shape-preserving effective size reduction of the AgNPs causes decrease in the strength of LSPR.

Fabry-P�rot (FP) modes of a dielectric cavity with a planar distribution of metal nanoparticles at one end have been studied numerically. An unusual enhancement in the strength of FP modes is observed close to the strong localized surface plasmon resonance of the metal nanoparticles. Experimental evidence for the numerical results has been provided by studying ZnO thin film cavities with Ag (Au) nanoparticles at one end. The enhancement in FP resonances has been interpreted in terms of a redefined cavity having a strongly dispersive adjacent medium. � 2014 AIP Publishing LLC.

Rayleigh scattering is usually considered to be the elastic scattering of photons from subwavelength physical objects, such as small particles or molecules. Here, we present a quantitative spectroscopic study of the scattering properties of molecules embedded in an optical cavity under strong coupling conditions, where the collective interaction between the molecules and the cavity gives rise to composite light-matter excitations known as cavity polaritons. We show that the polaritonic states exhibit strong resonant Rayleigh scattering, which depends on both the coupling strength and detuning and reaching ∼25% efficiency. Since the polaritonic wave functions in such systems are delocalized, our observations correspond to the collective scattering of each photon from a large ensemble of molecules.