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We include the dataset corresponding to the figures of the paper "Nonlinear Optical Response of a Plasmonic Nanoantenna to Circularly Polarized Light: Rotation of Multipolar Charge Density and Near-Field Spin Angular Momentum Inversion" by M. Quijada, A. Babaze, J. Aizpurua, and A.G. Borisov, published in the journal ACS Photonics, with DOI: 10.1021/acsphotonics.3c00783 . The set includes data to generate: optical spectra, charge density maps, time evolution of multipolar moments, and all the plots in the paper.

In recent years, the discovery of numerous two-dimensional (2D) magnetic materials exhibiting unique magnetic and spin transport properties has opened up new possibilities for spintronics applications. While long-range ferromagnetic ordering is theoretically unstable in 2D systems due to strong thermal fluctuations, this can be overcome by introducing anisotropy, which breaks continuous symmetry and allows for the emergence of long-range order. But still, the magnetization magnitude in 2D systems depends on both the exchange interaction and the total effective field, even at low temperatures, in contrast to 3D systems in which the magnetization magnitude only depends on the exchange interaction. Thus, two-dimensional magnetization is fundamentally different than three-dimensional magnetization. In this dissertation, we employ a self-consistent Random Phase Approximation to analytically investigate magnetization in 2D systems, accounting for the significant spin fluctuations. We examine the impact of random fields on 2D magnets and reveal a shift from a second-order to a first-order phase transition. Additionally, we develop a two-dimensional quantum Stoner-Wohlfarth model, demonstrating the temperature dependence of hysteresis and astroid diagrams, which differs from the 3D case. Finally, our simulation of the magnetization reversal dynamics in a 2D single-domain magnet shows that the process usually involves magnetization collapse followed by remagnetization in the direction of the external field, resulting in a significantly shorter reversal time.

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light–matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.

The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light–matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.

The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared single-cycle pulse pairs, we measure interferometric autocorrelations of the ultrafast currents induced by optical field emission at the nanogap of a single plasmonic nanocircuit. The dynamics of this ultrafast electron nanotransport depends on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrier-envelope phase. Quantitative modelling of the experiments enables us to monitor the spatiotemporal evolution of the electron density and currents induced in the system and to elucidate the physics underlying the electron transfer driven by strong optical fields in plasmonic gaps. Specifically, we clarify the interplay between the carrier-envelope phase of the driving pulse, plasmonic resonance and quiver motion.

In the wake of the Covid-10 pandemic, the Baltic region saw a dramatic reduction in tourist flows in 2000-2021; the decrease was as much as tenfold in some destinations. This study aims to classify the 16 transboundary tourist and recreational mesoregions of the Baltic region according to 2019 tourist flows. The research evaluates, for the first time, the 2020-2021 decline in tourist flows across these regions. The main outcome of this study is grouping the mesoregions into three orders according to the size of 2019 tourist flows. Four mesoregions were assigned to the first order (with over 500,000 arrivals), three of them located in the southwest Baltic region; nine, the second order (from 100,000 to 500,000 arrivals); three, the third order (from 50,000 to 100,000 arrivals). The most substantial fall in tourist flows occurred in 2020-2021 in the mesoregins including Sweden and Russia and the least marked in those involving Denmark, Germany, Finland, Estonia and Latvia. The findings may help track the future restoration of transboundary tourist flows in the countries of the Baltic region.

Recent work has shown that ElectroMagnetic Ion Cyclotron (EMIC) waves tend to occur in four distinct regions, each having their own characteristics and morphology. Here, we use nonlinear test-particle simulations to examine the range of energetic electron scattering responses to two EMIC wave groups that occur at low L-shells and overlap the outer radiation belt electrons. The first group consists of low-density, H-band region b waves, and the second group consists of high-density, He-band region c waves. Results show that while low-density EMIC waves cannot precipitate electrons below ∼16 MeV, the high density EMIC waves drive a range of linear and nonlinear behaviors including phase bunching and trapping. In particular, a nonlinear force bunching effect can rapidly advect electrons at low pitch-angles near the minimum resonant energy to larger pitch angles, effectively blocking precipitation and loss. This effect contradicts conventional expectations and may have profound implication for observational campaigns.

Sustainability has been a political focus of a broad spectrum of groups during the last decades. Other sustainable development indicators have been used in recent research, like in the United Nations, where they established SDIs for the 17 Sustainable Development Goals. Shifting to the Doughnut Economics framework aligns with the dual goals of sustainable development, which include moving everyone beyond social foundations and lowering stress on the biophysical system within planetary boundaries. As a response to measuring one’s country’s sustainability, quantifying the doughnut through the Sustainability Window approach specifies the lowest level of economic development required to meet social sustainability standards and the most significant level of economic development that does not exceed the environmental sustainability limit. This approach in measuring sustainable development proves to be useful in developing countries like the Philippines.

The Batagay megaslump, a permafrost thaw feature in north-eastern Siberia, provides access to ancient permafrost up to ∼650 kyr old. We aimed to assess the permafrost-locked organic matter (OM) quality and to deduce palaeo-environmental information on glacial–interglacial timescales. We sampled five stratigraphic units exposed on the 55 m high slump headwall and analysed lipid biomarkers (alkanes, fatty acids and alcohols). Our findings revealed similar biogeochemical signatures for the glacial periods: the lower ice complex (Marine Isotope Stage (MIS) 16 or earlier), the lower sand unit (sometime between MIS 16–6) and the upper ice complex (MIS 4–2). The OM in these units has a terrestrial character, and microbial activity was likely limited. Contrarily, the n-alkane and fatty acid distributions differed for the units from interglacial periods: the woody layer (MIS 5), separating the lower sand unit and the upper ice complex, and the Holocene cover (MIS 1), on top of the upper ice complex. The woody layer, marking a permafrost degradation disconformity, contained markers of terrestrial origin (sterols) and high microbial decomposition (iso- and anteiso-fatty acids). In the Holocene cover, biomarkers pointed to wet depositional conditions and we identified branched and cyclic alkanes, which are likely of microbial origin. Higher OM decomposition characterised the interglacial periods. As climate warming will continue permafrost degradation in the Batagay megaslump and in other areas, large amounts of deeply buried ancient OM with variable composition and degradability are mobilised, likely significantly enhancing greenhouse gas emissions from permafrost regions.

The excitation of low-energy electron–hole pairs is one of the most relevant processes in the gas–surface interaction. An efficient tool to account for these excitations in simulations of atomic and molecular dynamics at surfaces is the so-called local density friction approximation (LDFA). The LDFA is based on a strong approximation that simplifies the dynamics of the electronic system: a local friction coefficient is defined using the value of the electronic density for the unperturbed system at each point of the dynamics. In this work, we apply real-time time-dependent density functional theory to the problem of the electronic friction of a negative point charge colliding with spherical jellium metal clusters. Our non-adiabatic, parameter-free results provide a benchmark for the widely used LDFA approximation and allow the discussion of various processes relevant to the electronic response of the system in the presence of the projectile.

We use time-dependent density functional theory (TDDFT) within the jellium model to study the impact of quantum-mechanical effects on the self-interaction Green’s function that governs the electromagnetic interaction between quantum emitters and plasmonic metallic nanoantennas. A semiclassical model based on the Feibelman parameters, which incorporates quantum surface-response corrections into an otherwise classical description, confirms surface-enabled Landau damping and the spill out of the induced charges as the dominant quantum mechanisms strongly affecting the nanoantenna–emitter interaction. These quantum effects produce a redshift and broadening of plasmonic resonances not present in classical theories that consider a local dielectric response of the metals. We show that the Feibelman approach correctly reproduces the nonlocal surface response obtained by full quantum TDDFT calculations for most nanoantenna–emitter configurations. However, when the emitter is located in very close proximity to the nanoantenna surface, we show that the standard Feibelman approach fails, requiring an implementation that explicitly accounts for the nonlocality of the surface response in the direction parallel to the surface. Our study thus provides a fundamental description of the electromagnetic coupling between plasmonic nanoantennas and quantum emitters at the nanoscale.

The interactions of the excited states of a single chromophore with static and dynamic electric fields spatially varying at the atomic scale are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extension of the fields confined at the apex of a scanning tunneling microscope tip is smaller than that of the molecular exciton, a property used to generate fluorescence maps of the chromophore with intramolecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the picocavity junction formed by the chromophore, the tip, and the substrate reveal the key role played by subtle variations of Purcell, Lamb, and Stark effects. They also demonstrate that hyper-resolved fluorescence maps of the line shift and linewidth of the excitonic emission can be understood as images of the static charge redistribution upon electronic excitation of the molecule and as the distribution of the dynamical charge oscillation associated with the molecular exciton, respectively.

The dynamics of ultrafast electron currents triggered by femtosecond laser pulse irradiation of narrow gaps in a plasmonic dimer is studied using quantum mechanical Time-Dependent Density Functional Theory (TDDFT). The electrons are injected into the gap due to the optical field emission from the surfaces of the metal nanoparticles across the junction. Further evolution of the electron currents in the gap is governed by the locally enhanced electric fields. The combination of TDDFT and classical modelling of the electron trajectories allows us to study the quiver motion of the electrons in the gap region as a function of the Carrier Envelope Phase (CEP) of the incident pulse. In particular, we demonstrate the role of the quiver motion in establishing the CEP-sensitive net electric transport between nanoparticles.

Sweden's tourism industry stands out for its large contribution to the development of the national economy. The vast size of the country makes it possible to trace differences in incoming tourist flows from neighbouring countries. This circumstance accounts for the novelty of this study, which lies in viewing national tourism geography from the perspective of the theory of transboundary tourism-and-recreation region building. Interregional differences in the structure of incoming tourist flows help identify the country’s cross-border tourism-and-recreation regions and delineate their borders. This research employs statistical and cartographic methods. The incoming tourist flow to Sweden grew steadily until 2020. However, the Covid-19 crisis has led to a drastic reduction in the number of incoming tourists. Based on the 2019 statistics, the findings confirm the existence of a developed transboundary tourism-and-recreation mesoregion that brings together Germany, Denmark, and Sweden. The formation boasts strong tourist links. There are another five cross-border tourism-and-recreation mesoregions: Sweden-Norway-Denmark, Middle Sweden-Norway, Sweden-Norway-Finland, Middle Sweden-Finland, and South Sweden-Finland. The number of tourists visiting cross-border mesoregions indicates the degree of development of the latter.

The deposition of individual molecules, molecular networks, and molecular layers at surfaces is at the core of surface reactivity, energy harvesting, molecular electronics, and (single) photon sources. Yet, strong adsorbate–substrate interaction on metallic surfaces quenches the excited molecular states and harms many practical applications. Here, we theoretically address the role of a NaCl ionic crystal spacer layer in decoupling an adsorbate from the substrate and therefore changing the interplay between the competing decay channels of an excited molecule driven by electronic and electromagnetic interactions. A quantitative assessment of the corresponding decay rates allows us to establish the minimum thickness of the spacer required for the observation of molecular luminescence from the junction of a scanning tunneling microscope. Our work provides a solid quantitative theoretical basis relevant for several fields of nanotechnology where engineering of ionic crystal spacers allows for adsorbate charge manipulation, reactivity, and photon emission in nanocavities.

The optical response of a system formed by a quantum emitter and a plasmonic gap nanoantenna is theoretically addressed within the frameworks of classical electrodynamics and the time-dependent density functional theory (TDDFT). A fully quantum many-body description of the electron dynamics within TDDFT allows for analyzing the effect of electronic coupling between the emitter and the nanoantenna, usually ignored in classical descriptions of the optical response. We show that the hybridization between the electronic states of the quantum emitter and those of the metallic nanoparticles strongly modifies the energy, the width, and the very existence of the optical resonances of the coupled system. We thus conclude that the application of a quantum many-body treatment that correctly addresses charge-transfer processes between the emitter and the nanoantenna is crucial to address complex electronic processes involving plasmon–exciton interactions directly impacting optoelectronic applications.

We include the dataset corresponding to the figures of the paper "Electronic Exciton−Plasmon Coupling in a Nanocavity Beyond the Electromagnetic Interaction Picture" by A. Babaze, R. Esteban, A.G. Borisov, and J. Aizpurua, published in the journal Nano Letters, with DOI: 10.1021/acs.nanolett.1c03202 . The set includes data to generate: optical spectra, charge and current density maps, projected density of electronic states, and plots in the paper.

Gallid alphaherpesvirus 1 causes infectious laryngotracheitis (ILT) in farmed poultry worldwide. Intertypic recombination between vaccine strains of this virus has generated novel and virulent isolates in field conditions. In this study, in vitro and in ovo systems were co-infected and superinfected under different conditions with two genomically distinct and commonly used ILTV vaccines. The progeny virus populations were examined for the frequency and pattern of recombination events using multi-locus high-resolution melting curve analysis of polymerase chain reaction products. A varied level of recombination (0 to 58.9%) was detected, depending on the infection system (in ovo or in vitro), viral load, the composition of the inoculum mixture, and the timing and order of infection. Full genome analysis of selected recombinants with different in vitro phenotypes identified alterations in coding and non-coding regions. The ability of ILTV vaccines to maintain their capacity to recombine under such varied conditions highlights the significance of recombination in the evolution of this virus and demonstrates the capacity of ILTV vaccines to play a role in the emergence of recombinant viruses.

We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set to be resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow one to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system, allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work.

A novel technique for the investigation of the radiative contribution to the electromagnetic local density of states is presented. The inelastic tunneling current from a scanning tunneling microscope (STM) is used to locally and electrically excite the plasmonic modes of a triangular gold platelet. The radiative decay of these modes is detected through the transparent substrate in the far field. Emission spectra, which depend on the position of the STM excitation, as well as energy-filtered emission maps for particular spectral windows are acquired using this technique. The STM-nanosource spectroscopy and microscopy results are compared to those obtained from spatially resolved electron energy loss spectroscopy (EELS) maps on similar platelets. While EELS is known to be related to the total projected electromagnetic local density of states, the light emission from the STM-nanosource is shown here to select the radiative contribution. Full electromagnetic calculations are carried out to explain the experimental STM data and provide valuable insight into the radiative nature of the different contributions of the breathing and edge plasmon modes of the nanoparticles. Our results introduce the STM-nanosource as a tool to investigate and engineer light emission at the nanoscale.

In this joint experimental and theoretical study we demonstrate coherent control of the optical field emission and electron transport in plasmonic gaps subjected to intense single-cycle laser pulses. Our results show that an external THz field or a minor dc bias, orders of magnitude smaller than the optical bias owing to the laser field, allows one to modulate and direct the electron photocurrents in the gap of a connected nanoantenna operating as an ultrafast nanoscale vacuum diode for lightwave electronics. Using time-dependent density functional theory calculations we elucidate the main physical mechanisms behind the observed effects and show that an applied dc field significantly modifies the optical field emission and quiver motion of photoemitted electrons within the gap. The quantum many-body theory reproduces the measured net electron transport in the experimental device, which allows us to establish a paradigm for controlling nanocircuits at petahertz frequencies.

IntroductionQuantitative in vivo measurement of brain amyloid burden is important for both research and clinical purposes. However, the existence of multiple imaging tracers presents challenges to the interpretation of such measurements. This study presents a direct comparison of Pittsburgh compound B-based and florbetapir-based amyloid imaging in the same participants from two independent cohorts using a crossover design.MethodsPittsburgh compound B and florbetapir amyloid PET imaging data from three different cohorts were analyzed using previously established pipelines to obtain global amyloid burden measurements. These measurements were converted to the Centiloid scale to allow fair comparison between the two tracers. The mean and inter-individual variability of the two tracers were compared using multivariate linear models both cross-sectionally and longitudinally.ResultsGlobal amyloid burden measured using the two tracers were strongly correlated in both cohorts. However, higher variability was observed when florbetapir was used as the imaging tracer. The variability may be partially caused by white matter signal as partial volume correction reduces the variability and improves the correlations between the two tracers. Amyloid burden measured using both tracers was found to be in association with clinical and psychometric measurements. Longitudinal comparison of the two tracers was also performed in similar but separate cohorts whose baseline amyloid load was considered elevated (i.e., amyloid positive). No significant difference was detected in the average annualized rate of change measurements made with these two tracers.DiscussionAlthough the amyloid burden measurements were quite similar using these two tracers as expected, difference was observable even after conversion into the Centiloid scale. Further investigation is warranted to identify optimal strategies to harmonize amyloid imaging data acquired using different tracers.

The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared single-cycle pulse pairs, we measure interferometric autocorrelations of the ultrafast currents induced by optical field emission at the nanogap of a single plasmonic nanocircuit. The dynamics of this ultrafast electron nanotransport depends on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrier-envelope phase. Quantitative modelling of the experiments enables us to monitor the spatiotemporal evolution of the electron density and currents induced in the system and to elucidate the physics underlying the electron transfer driven by strong optical fields in plasmonic gaps. Specifically, we clarify the interplay between the carrier-envelope phase of the driving pulse, plasmonic resonance and quiver motion.

We developed a computational framework for simulating thin fluid flow in narrow interfaces between contacting solids, which is relevant for a range of engineering, biological and geophysical applications. The treatment of this problem requires coupling between fluid and solid mechanics equations, further complicated by contact constraints and potentially complex geometrical features of contacting surfaces. We developed a monolithic finite-element framework for handling mechanical contact, thin incompressible viscous flow and fluid-induced tractions on the surface of the solid, suitable for both one- and two-way coupling approaches. Additionally, we consider the possibility of fluid entrapment in "pools" delimited by contact patches and its pressurisation following a non-linear compressibility constitutive law. Furthermore, image analysis algorithms were adapted to identify the local status of each interface element within the Newton-Raphson loop. First, an application of the proposed framework for a problem with a model geometry is given, and the robustness is demonstrated by the residual-wise and status-wise convergence. The full capability of the developed two-way coupling framework is demonstrated on a problem of a fluid flow in contact interface between a solid with representative rough surface and a rigid flat. The evolution of the contact pressure, fluid flow pattern and the morphology of trapped fluid zones until the complete sealing of the interface is displayed. Additionally, we demonstrated an almost mesh-independent result of a refined post-processing approach to the real contact-area computation. The developed framework permits not only to study the evolution of effective properties of contact interfaces, but also to highlight the difference between one- and two-way coupling approaches and to quantify the effect of multiple trapped fluid "pools" on the coupled problem., Comment: 38 pages, 15 figures

1 oktober 2018, Item does not contain fulltext, The 31(st) International Conference on Antiviral Research (ICAR) was held in Porto, Portugal from June 11-15, 2018. In this report, volunteer rapporteurs provide their summaries of scientific presentations, hoping to effectively convey the speakers' goals and the results and conclusions of their talks. This report provides an overview of the invited keynote and award lectures and highlights of short oral presentations, from the perspective of experts in antiviral research. Of note, a session on human cytomegalovirus included an update on the introduction to the clinic of letermovir for the prevention of CMV infection and disease. The 31(st) ICAR successfully promoted new discoveries in antiviral research and drug development. The 32(nd) ICAR will be held in Baltimore, Maryland, USA, May 6-10, 2019.

In 2004, the Pskov - Livonia Euroregion was established across the borders of Estonia, Latvia and Russia (the Pskov region). Tourism became a cooperation priority in the Euroregion. This necessitated research on the local tourism and recreation areas. This study aims to estimate the development prospects of transboundary microregions which have been identified by the authors within the Latvian-Estonian-Russian tourism and recreation mesoregion. The authors employ ten additional criteria proposed in the general conception of transboundary tourism and recreation regions. The article identifies five microregions: Pskov-Pechory- Tartu and Pskov-Izborsk-Cesis (first level), Pytalovo-Rezekne (second level), and Izborsk- Pechory district- Setomaa and Lake Chudskoe area (third level). The authors classify the microregions according to their level of development. The development of the Izborsk-Pechory district-Setomaa microregion is defined as ‘above average’, that of Pskov-Pechory-Tartu as ‘average’, and that of Pskov-Izborsk-Cesis as ‘below average’, and finally, the development of Pytalovo-Rezekne microregion is described as ‘poor’. The Lake Chudskoe area microregion is classified as an ‘emerging’ one. The overall level of development of transboundary tourism and recreation microregions is assessed as ‘below average’. The results of the study can be used in preparing recommendations for the development of transboundary microregions within the Latvian-Estonian-Russian tourism and recreation mesoregion.

Localized plasman excitations in metallic nanoparticles allow for generation of very strong electromagnetic fields in subwavelength regions. Most studies focus on the linear response of these plasmonic systems, but nonlinear optical effects have also been studied both theoretically and experimentally. Controlling these nonlinear effects can be useful for (bio-) imaging and generation of attosecond XUV laser pulses, among others. In centrosymmetric systems, only light at odd-multiples of the incident frequency (odd-order harmonics) is emitted to the far-field region. In order to obtain even-order harmonics in the far-field, breaking the symmetry is necessary. which can be achieved, for example, by applying a permanent polarizing electric field. On the other hand, the analysis of the near fields shows that multipole even-order components exist in the proximity of the metallic surface, even in the absence of the permanent electric field. A promising alternative to detect even harmonics in the far-field is to use a molecule as a resonant nanoantenna that scatters the local near fields. In this work, we use Time-Dependent Density Functional (TDDFT) simulations to study how the presence of a molecule affects the nonlinear response of the plasmonic system (Figure 1). We place a molecule, considered as a point dipole, close to a plasmonic nanosphere and analyze the emission of the high harmonics when the molecule interacts with the nanoparticle's near fields.

The ability of plasmonic resonances to strongly localize and enhance electromagnetic fields at the surface of metallic nanoparticles can be utilized to produce strong-field photoemitted electrons. If two plasmonic nanoparticles are separated by a small gap, the photoemitted electrons create femtosecond currents between the nanoparticles, which can be controlled by varying the Carrier-Envelope Phase (CEP) of a single optical-cycle light pulse. Due to the strongly decaying electric near-fields around plasmonic nanoparticles, in single particle configurations, photoemitted electrons follow a straight trajectory and do not present quiver motion however, a much richer electron dynamics is produced when the emission of electrons occurs in a plasmonic gap. Using Time Dependent Density Functional Theory (TDDFT) we theoretically investigate the photo-induced currents across the gap between two cylindrical nanoparticles as a response to a single-cycle optical pulse. Contrary to the single nanoparticle case, the electric field in the gap region does not decay abruptly along the dimer axis. We demonstrate that in such scenario, the photoemitted electrons experience quiver motion that responds to the complex structure of the fields induced in the gap. This effect is compared to the case where no quiver motion is produced i.e., when the maximum current occurs for a perfect cosine-like optical pulse (CEP=0). We find that the quiver motion results in a shift of the CEP at which the maximum current is observed. Tracing and dissecting an ultrashort photocurrent in a plasmonic nanogap as shown here is relevant for the proper design of integrated optoelectronic devices that operate in the single-electron regime.

We report on the theoretical study of the second and third harmonic generation in plasmonic dimer nanoantennas with narrow gaps. Our study is based on the time dependent density functional theory. This allows us to address the nonlinear response of a tunneling junction in a subnanometric plasmonic gaps with a quantum calculation, which goes beyond conventional classical local and nonlocal treatments. We demonstrate that the nonlinear electron transport in a plasmonic junction, associated to the corresponding strong field enhancement in the narrow gap, allows to reach orders of magnitude enhancement in the efficiency of the second and third harmonic generation. Depending on the size of the junction and the frequency of the fundamental incident wave, we show that the frequency conversion in plasmonic dimer gaps can be determined by (i) the intrinsic nonlinearity of each individual nanoparticle, (ii) the nonlinear ac tunneling current across the gap, and (iii) the resonant excitations of the plasmon modes of the dimer. The study of the nonlinear response of plasmonic gaps within a full quantum treatment allows us to understand the fundamental mechanisms of nonlinearity in nanoplasmonics.

Research on topologically protected chiral magnetic structures such as magnetic domain walls (DWs) and skyrmions, have gained extensive interest because of their possible applications in magnetic data storage industries. The recently observed chiral DW structures in ultrathin ferromagnetic lms with perpendicular magnetic anisotropy has been attributed to the presence of a strong Dzyaloshinskii-Moriya interaction (DMI). In this thesis, the DMI mediated by the conduction electrons in two dimensional magnetic systems such as magnetic thin lms or at the interfaces between two magnetic materials has been studied. I calculate the Ruderman-Kittel- Kasuya-Yosida (RKKY) type indirect exchange coupling between two magnetic moments at nite temperature using the free electron band. At high temperature, the coupling strength decays with distance faster than the coupling at zero temperature but the period of oscillation remains same. However, the free electron band alone could not produce DMI. In the next step, I show addition of Rashba spin-orbit coupling (RSOC) with the spin-polarized conduction electron band produces the DMI between two magnetic ions. The essential feature of this DMI is: the coupling strength increases with the strength of RSOC, but decreases signi cantly with the Heisenberg exchange coupling. The DMI calculated with this model well explains the possibility of preferred Neel or Bloch DW structures with specifc chirality. In addition: I study switching of magnetization with ultrafast laser pulse by inverse Faraday e ect (IFE) where an optically induced non-equilibrium orbital momentum generates an e ective magnetic eld via spin-orbit coupling for magnetization switching. I calculate the magnitude of induced orbital moment for the generic itinerant band and show that magnitude is not large enough to make the switching by a single pulse, however, switching could be possible if multiple pulses are applied to the material.

Ethnocultural diversity of the Russian Federation is not only an important component of its historical heritage but also a significant resource for development. However, a number of ethnic groups are on the brink of extinction. The aim of this study is to investigate the impact of changes in state and administrative borders on the territorial and demographic development of small ethnic groups. The article analyses the case of three Baltic Finnish peoples living in the Russian North-West and divided by borders of different levels: Karelians (Finland, the Republic of Karelia, and the Leningrad and Tver regions), Vepsians (the Republic of Karelia and the Leningrad and Vologda regions), and Setos (Estonia and the Pskov region). The analysis is based on the cartographic and statistical demographic data, as well as the results of a complex expedition made in summer 2014 in the Pechory district of the Pskov region. The results of the study show that the assimilation of peoples divided as a result of migration and di vision of their ethnic territory by political borders takes place at an accelerated rate. The study makes it possible to formulate certain recommendations and improve the measures to maintain the language and culture of ethnic minorities of the Russian North-West.

Lake Cadagno (26 ha) is a crenogenic meromictic lake located in the Swiss Alps at 1921 m asl with a maximum depth of 21 m. The presence of crystalline rocks and a dolomite vein rich in gypsum in the catchment area makes the lake a typical “sulphuretum ” dominated by coupled carbon and sulphur cycles. The chemocline lies at about 12 m depth, stabilized by density differences of salt-rich water supplied by sub-aquatic springs to the monimolimnion and of electrolyte-poor surface water feeding the mixolimnion. Steep sulphide and light gradients in the chemocline support the growth of a large bacterial plume (up to 107 cells ml−1) dominated by green sulphur bacteria (GSB) of the genus Chlorobium and purple sulphur bacteria (PSB) of the Chromatiaceae family. Since the early Holocene (10.5–8 cal kyr BP), PSB and GSB are showing long-term alternation in abundance and relative dominance. Key species are Chlorobium clathratiforme , Thiocystis chemoclinalis , Thiocystis cadagnonensis , Candidatus “ Thiodictyon syntrophicum ” and Chromatium okenii ; the latter represents only 0.3 % of the total cell number but due to its big size and high activity can contribute up to 70 % of the total carbon uptake in the chemocline. Small-celled PSB together with the sulfate-reducing bacterium Desulfocapsa thiozymogenes sp. form stable aggregates in the lake, which represent small microenvironments with an internal sulphur cycle. Eukaryotic primary producers in the anoxic zones are dominated by Cryptomonas phaseolus , whereas eukaryotic heterotrophs are represented by ciliates and choanoflagellates, but a clade of heteroloboseans and two novel clades distantly related to opisthokonts and Cercozoa are also present. Zooplankton and fish abundance in the mixolimnion of this model ecosystem are linked via food web to the chemocline microbial plume, consequently anaerobic primary production supports relative high fish productivity in the lake.

Excitation of localized surface plasmon resonances in metal nanoparticles and nanoparticle assemblies allows to manipulate light at nanometer scales well beyond the wavelength and opens the possibility of many applications. The complexity of the variety of methods to fabricate plasmonic structures and the sophistication of optical characterization techniques invites for completing the plasmonics landscape with a comprehensive theoretical understanding of the optical response. Classical approaches based on the solution of Maxwell’s equations using local (model or empirical) bulk dielectric constant are extensively used to describe plasmonic systems and gain the necessary intuition. At the same time, recent experimental and theoretical developments have clearly demonstrated that as soon as nanometer and subnanometer scales are approached, quantum effects such as tunneling, non-local screening and the atomistic structure of the metal nanoparticles become important. In this chapter, we discuss the major manifestations of quantum effects in the properties of localized plasmons, with particular emphasis on the underlying physics.

The optical response in metallic nanoantennas can be actively controlled by application of external bias, polarizing fields, or charging. By analysing the electron gas dynamics and response with time-dependent density functional theory (TDDFT), the potential of such active control in metallic nanogaps and clusters is shown.

We present a combined theoretical and experimental study of the energy loss of H2+ molecular ions interacting with thin oxide and carbon films. As a result of quantum mechanical interference of the target electrons, the energy loss of a molecular projectile differs from the sum of the energy losses of individual atomic projectiles. This difference is known as the vicinage effect. Calculations based on the time-dependent density functional theory allow the first-principles description of the dynamics of target excitations produced by the correlated motion of the nucleons forming the molecule. We investigate in detail the dependence of the vicinage effect on the speed and charge state of the projectile and find an excellent agreement between calculated and measured data.

The optical response of small charged metallic nanodisks of one atomic monolayer thickness is analyzed under the excitation by an incident plane wave and by a localized pointlike dipole. Using the time-dependent density functional theory (TDDFT) and classical electrodynamical calculations we identify the bright and dark plasmon modes and study their evolution under external charging of the nanostructure. For neutral nanodisks, despite their monolayer thickness, the in-plane optical response, as obtained from TDDFT, is in agreement with classical electromagnetic results. The optical response for an incident wave polarized perpendicular to the nanostructure cannot be retrieved classically as it reflects a discrete energy structure of electronic levels. This latter situation appears most sensitive to external charging while the energy of the in-plane plasmon with dipolar character is nearly charge independent.

The nonlinear response of metallic nanoparticles is obtained from quantum time dependent density functional theory calculations. Without any aprioristic assumption our calculations allow us to identify high-order harmonic generation in canonical plasmonic structures such as spherical single particles and dimers. Furthermore, we demonstrate that under currently available experimental conditions, the application of an external polarizing field to the nanoparticles allows to actively control even-order harmonic generation in otherwise symmetry forbidden situations. Our quantum calculations provide quantitative access to the high-order response of metallic nanoantennas, which is of utmost importance in the design, control, and exploitation of optoelectronic devices as well as in the generation of extreme ultraviolet radiation.

We use a time-dependent density functional theory approach to study the optical response of a hybrid nanostructure where the junction between thin metallic films is functionalized with a quantum well (QW) structure. We show that an unoccupied QW-localized electronic state opens the possibility of the active electrical control of the photoassisted electron transport through the junction and of the absorption at optical frequencies. Control strategies based on an applied bias or an external THz field are demonstrated.

The self-consistent electron-ion potential V(r) is calculated for H ions in an electron gas system as a function of the projectile energy to model the electronic stopping power for conduction-band electrons. The results show different self-consistent potentials at low projectile-energies, related to different degrees of excitation of the electron cloud surrounding the intruder ion. This behavior can explain the abrupt change of velocity dependent screening-length of the potential found by the use of the extended Friedel sum rule and the possible breakdown of the standard free electron gas model for the electronic stopping at low projectile energies. A dynamical interpolation of V(r) is proposed and used to calculate the stopping power for H interacting with the valence electrons of Al. The results are in good agreement with the TDDFT benchmark calculations as well as with experimental data.

The objective of this thesis is to reach theoretical understanding of the unusual relationship between charge-ordering and superconductivity in correlated-electron systems. The competition between these broken symmetries and magnetism in the cuprate high temperature superconductors has been extensively discussed, but exists also in many other correlated-electron superconductors, including quasi-two-dimensional organic charge-transfer solids. It has been suggested that the same attractive interaction is responsible for both charge-order and superconductivity. We propose that the specific interaction is the tendency in correlated-electron systems to form spin-singlet bonds, which is strongly enhanced at the commensurate carrier density p of ½ a charge carrier per site, characteristic of all superconducting charge-transfer solids. To probe superconductivity driven by electron correlations, a necessary condition is that electron-electron interactions enhance superconducting pair-pair correlations, relative to the non-interacting limit. We have performed state of the art numerical calculations on the two-dimensional Hubbard model on different triangular lattices, as well as other lattices corresponding to K-BEDT-TTF based organic charge transfer solids, for the complete range of carrier densities per site p (0 ≤ p ≤ 1). We have shown that pair-pair correlation for each cluster is enhanced by electron-electron interaction only for p ≃ 0.5, far away from the density range thought to be important for superconductivity. Although initial focus is on charge-transfer solids, the results of the research will impact the field of correlated electrons as a whole. We believe our calculations will provide fundamental and fresh insight to the theory of superconductivity in strongly correlated systems.

Metallic structures with nanogap features have proven highly effective as building blocks for plasmonic systems, as they can provide a wide tuning range of operating frequencies and large near-field enhancements. Recent work has shown that quantum mechanical effects such as electron tunnelling and nonlocal screening become important as the gap distances approach the subnanometre length-scale. Such quantum effects challenge the classical picture of nanogap plasmons and have stimulated a number of theoretical and experimental studies. This review outlines the findings of many groups into quantum mechanical effects in nanogap plasmons, and discusses outstanding challenges and future directions.

Using the time-dependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spill-out from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment.

The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 1012 A cm−2, the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics.

We report a quantum mechanical study of the plasmonic response of bimetallic spherical core/shell nanoparticles. The systems comprise up to 104 electrons and their optical response is addressed with Time Dependent Density Functional Theory calculations. These quantum results are compared with classical electromagnetic calculations for core/shell systems formed by Al/Na, Al/Au and Ag/Na, as representative examples of bimetallic systems. We show that for shell widths in the nanometer range, the system cannot be described as a simple stack of two metals. The finite size effect and the transition layer formed between the core and the shell strongly modify the optical properties of the compound nanoparticle. In particular this configuration leads to a frequency shift of the plasmon resonance with shell character and an increased plasmon decay into electron-hole pairs which eventually quenches this resonance for very thin shells. This effect is difficult to capture with a classical theory even upon adjustment of the parameters of a combination of metallic dielectric functions.

The unique properties of localized surface plasmons have turned plasmonic nanoparticles into a suitable platform for novel and more efficient optoelectronic processes. Therefore, the development of practical approaches to actively control the plasmon excitations is a major fundamental and practical challenge. Using Time Dependent Density Functional Theory we explore the possibility of all electrical control of the optical properties of different plasmonic systems such as isolated nanoparticles as well as nanoparticle dimers, and core-shell nanoparticles with sub nm gaps. We demonstrate that for plasmonic systems with narrow gaps, the quantum regime owing to the electron tunneling offers the possibility of fast and reversible control of the plasmon resonances, by application of an external dc bias. Along with all-electrical control of the linear response, we also show that the external polarizing DC field can be used to actively control high-harmonic generation from plasmonic nanoparticles.