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We employ the first-principles calculation with non-equilibrium Green's function method to comprehensively investigate the crucial role of interfacial geometry in spin transport properties of Co/1,4-benzenediamine (BDA)/Co single-molecule magnetic junctions (SMMJs). Two bonding mechanisms are proposed for the hard-hard Co-N coupling: (1) the covalent bonding between the H-dissociated amine linker and spin-polarized Co apex atoms and (2) the dative interaction between the H-non-dissociated (denoted by +H) amine linker and Co apex atoms. The former covalent contact dominates the π-resonance interfacial spin selection that can be well preserved in H-dissociated cases regardless of the choice of top, bridge, and hollow contact sites. From our detailed analyses of spin-polarized transmission spectra, local density of states, and molecular density of states, the underlying mechanism is that the strong hybridization between Co-d, N-p y , and the π-orbital of the phenyl ring in dissociated cases renders the 2-fold HOMO (4-fold LUMO) of the central molecule closer to the Fermi energy. In contrast, the enlarged Co-N bond length of the latter dative contact in the H-non-dissociated case not only destroys the spinterface coupling but also blocks the spin injection. This theoretical work may provide vital and practical insights to illustrate the spin transport property in real amine-ended SMMJs since the contact geometries and interfacial bond mechanisms remain unclear during the breaking junction technique.

The transport property of a four-terminal MoS2NR/V7(Bz)8 device is computed within the framework of density functional theory combined with the nonequilibrium Green’s function (NEGF) technique. This device is constructed by a MoS2 nanoribbon (MoS2NR) as the source-to-drain channel and a spin-polarized V7(Bz)8 nanowire grafted on the MoS2NR surface as the double gate channel, where the four terminals are all connected to a semi-infinite one-dimensional (1D) Au lead. The transport characteristic is explored by investigating the conductance, currents, local density of states (LDOS), and scattering states. The currents of different leads are dissimilar due to the complex interplay between the four terminals that is otherwise not present in a two-terminal setup. The most interesting feature we articulate is that the induced promising properties including negative differential resistance (NDR) behavior, input/output current switching, as well as spin-polarized lead currents can be fine-tuned by the magnitude of either source bias or gate bias. These features can be utilized in designing multi-terminal nanoelectronic devices.

The vortex states in electron-doped high-Tc superconductors are studied theoretically at the mean-field approach and based on the Bogoliubov-de Gennes equations. The local density of states is calculated, through which the in-gap bound states are revealed. They are robust at the sites around the vortex core. In the underdoped region where the antiferromagnetic order and the superconducting order coexist, the in-gap peaks are lying symmetric with respect to the Fermi energy, while the peak intensities at the negative energy are much stronger. A stripe-type modulation is revealed for the spin-resolved local density of states. As the doping density increases to the optimal or over-doped region, the long-range antiferromagnetic order disappears, and the two in-gap peaks merge to one single peak. The peak position is near the Fermi energy. Our results indicate that the vortex states may be used to detect the signature of the antiferromagnetic order in electron-doped high-Tc superconductors.

Usually, the cavity is considered an intrinsic part of laser design to enable coherent emission. For different types of cavities, it is assumed that the light coherence is achieved by different ways. We show that regardless of the type of cavity, the lasing condition is universal and is determined by the ratio of the width of the atomic spectrum to the product of the number of atoms and the spontaneous radiation rate in the laser structure. We demonstrate that cavity does not play a crucial role in lasing since it merely decreases the threshold by increasing the photon emission rate thanks to the Purcell effect. A threshold reduction can be achieved in a cavity-free structure by tuning the local density of states of the electromagnetic field. This paves the way for the design of laser devices based on cavity-free systems.

VO2 is a highly correlated electron system which has a metal-to-insulator transition (MIT) with a dramatic change of conductivity accompanied by a first-order structural phase transition (SPT) near room temperature. The origin of the MIT is still controversial and there is ongoing debate over whether an SPT induces the MIT and whether the Tc can be engineered using artificial parameters. We examined the electrical and local structural properties of Cr- and Co-ion implanted VO2 (Cr-VO2 and Co-VO2) films using temperature-dependent resistance and X-ray absorption fine structure (XAFS) measurements at the V K edge. The temperature-dependent electrical resistance measurements of both Cr-VO2 and Co-VO2 films showed sharp MIT features. The Tc values of the Cr-VO2 and Co-VO2 films first decreased and then increased relative to that of pristine VO2 as the ion flux was increased. The pre-edge peak of the V K edge from the Cr-VO2 films with a Cr ion flux ≥ 1013 ions/cm2 showed no temperature-dependent behavior, implying no changes in the local density of states of V 3d t2g and eg orbitals during MIT. Extended XAFS (EXAFS) revealed that implanted Cr and Co ions and their tracks caused a substantial amount of structural disorder and distortion at both vanadium and oxygen sites. The resistance and XAFS measurements revealed that VO2 experiences a sharp MIT when the distance of V–V pairs undergoes an SPT without any transitions in either the VO6 octahedrons or the V 3d t2g and eg states. This indicates that the MIT of VO2 occurs with no changes of the crystal fields.

Magic-angle twisted bilayer graphene (MATBG) exhibits a range of correlated phenomena that originate from strong electron-electron interactions. These interactions make the Fermi surface highly susceptible to reconstruction when ±1, ±2 and ±3 electrons occupy each moire unit cell, and lead to the formation of various correlated phases1-4. Although some phases have been shown to have a non-zero Chern number5,6, the local microscopic properties and topological character of many other phases have not yet been determined. Here we introduce a set of techniques that use scanning tunnelling microscopy to map the topological phases that emerge in MATBG in a finite magnetic field. By following the evolution of the local density of states at the Fermi level with electrostatic doping and magnetic field, we create a local Landau fan diagram that enables us to assign Chern numbers directly to all observed phases. We uncover the existence of six topological phases that arise from integer fillings in finite fields and that originate from a cascade of symmetry-breaking transitions driven by correlations7,8. These topological phases can form only for a small range of twist angles around the magic angle, which further differentiates them from the Landau levels observed near charge neutrality. Moreover, we observe that even the charge-neutrality Landau spectrum taken at low fields is considerably modified by interactions, exhibits prominent electron-hole asymmetry, and features an unexpectedly large splitting between zero Landau levels (about 3 to 5 millielectronvolts). Our results show how strong electronic interactions affect the MATBG band structure and lead to correlation-enabled topological phases.

We examine the transport properties of multi-channels of a porphyrin phenylacetylene (PPA) molecule by changing gate and source voltages at its two terminals. Density functional theory (DFT) within the non-equilibrium Green's function framework (NEGF) is employed to calculate the four probe PPA device by connecting with four Au electrodes using S linkages. Two gate voltages are chosen as 0.6 V (denoted as PPA-0.6) and 1.0 V (denoted as PPA-1.0), respectively. At each certain gate voltage, source voltages are applied in the range of 0.0 V to 1.0 V at a step of 0.2 V. It is found that the magnitude of the gate voltage plays a significant role in the whole transport property. No matter in PPA-0.6 or in PPA-1.0, evident NDR behavior is observed for lead currents. Moreover, a smaller gate voltage could induce a more prominent NDR effect. On the other hand, the relative magnitude of the gate voltage and the source voltage determines the current directions of the gate and source leads. Furthermore, input/output current switches can be achieved for the gate lead at the critical voltage of Vgate = Vsource. These interesting transport characteristics are further analyzed from the transmission spectra and the local density of states (LDOS). This presentation provides a clue for exploring novel functional nano-electronic molecular devices based on PPA by tuning gate voltages and source voltages as well as changing lead-to-lead channels.

Density functional theory method was used to study the interaction of 3d-transition metal ions with divacancy in graphene. Calculations demonstrate that in all cases, except for that of the structure with the Sc ion, the metal is located in the divacancy center, compensating for the four dangling chemical bonds of carbon atoms. Interaction energies are close to 1000 kJ/mol. The strongest interaction was found for the Ni ion. Analysis of the local density of states of nanoparticles shows that additional energy levels appear in the energy gap between the highest occupied and lowest unoccupied levels of the graphene cluster due to the presence of a transition metal ion. In the case of clusters with Co, Ti, and V ions, the highest occupied level of the cluster lies in the region of electronic states with non-zero local density on the ion.

Using density functional theory (DFT) calculations, we examined the effects of substitutional doping on the formation of Cu vacancies in Cu2O(111). Upon replacing coordinatively unsaturated O with other elements (N, F, P, S, and Cl) and calculating the formation energies, we found that compared to the undoped surface, Cu vacancy formation is most favorable in the F-doped surface and least favorable in the N-doped Cu2O(111) surface. In addition, we found that in most cases, vacancy formation of the coordinatively saturated Cu has higher vacancy formation energy than coordinatively unsaturated Cu atoms. In the electron localization function plots and the projected charge distributions of the local density of states, we found bonding enhancement between Cu and N in N-Cu2O(111) but no corresponding enhancement was observed in the F-doped surface. Our results showed that the interaction between the substitutional dopants and the Cu atoms affects the formation of the doped system and the Cu vacancy formation in the surface.

Layered metal-dielectric structures are easy-to-fabricate one-dimensional plasmonic metamaterials. Using the effective media approach, we consider surface plasmons that appear on an interface between such metamaterial and a dielectric. We have shown that two types of surface plasmon states appear on an interface. The frequency of the peak in the local density of states of these states is dependent on the fraction of metal in the metamaterial. By reducing the fraction, the frequency can be shifted towards longer wavelengths. There the losses of light in metal are reduced, which, as we have shown, leads to the increase in peak value of the Purcell factor.

Optical nanoantennas are well-known for the confinement of light into nanoscale hot spots, suitable for emission enhancement and sensing applications. Here, we show how control of the antenna dimensions allows tuning the local optical phase, hence turning a hot spot into a cold spot. We manipulate the local intensity exploiting the interference between driving and scattered field. Using single molecules as local detectors, we experimentally show the creation of subwavelength pockets with full suppression of the driving field. Remarkably, together with the cold excitation spots, we observe inhibition of emission by the phase-tuned nanoantenna. The fluorescence lifetime of a molecule scanned in such volumes becomes longer, showing slow down of spontaneous decay. In conclusion, the spatial phase of a nanoantenna is a powerful knob to tune between enhancement and inhibition in a 3-dimensional subwavelength volume.

A novel family of disordered systems is proposed. This family belongs to the class of systems containing random substitutional non-Hermitian impurities. We limit our consideration to a rather simple case when the presence of substitutional point defects results in the model Hamiltonian featuring a diagonal disorder. In contrast to known models of non-Hermitian impurities, the nonzero density of states for each isolated from the host impurity is restricted to a continuous band of finite width. A method to construct corresponding impurity Hamiltonians is provided.

Using scanning tunneling microscopy/spectroscopy (STM/STS), we examine quasiparticle scattering and interference properties at the surface of WTe2. WTe2, layered transition metal dichalcogenide, is predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 emerge as topologically protected touching points of electron and hole pockets, and Fermi arcs connecting them can be visible in the spectral function on the surface. To probe the properties of surface states, we have conducted low-temperature STM/STS (at 2.7 K) on the surfaces of WTe2 single crystals. We visualize the surface states of WTe2 with atomic scale resolution. Clear surface states emerging from the bulk electron pocket have been identified and their connection with the bulk electronic states shows good agreement with calculations. We show the interesting double resonance peaks in the local density of states appearing at localized impurities. The low-energy resonant peak occurs near the Weyl point above the Fermi energy and it may be mixed with the surface state of Weyl points, which makes it difficult to observe the topological nature of the Weyl semimetal WTe2.

Cathodoluminescence can probe photonic responses of nanostructures at high spatial and energy resolution, providing a powerful tool to investigate the radiative properties under electron excitation...

Graphene nanoribbons (GNRs) attract a growing interest due to their tunable physical properties and promise for device applications. A variety of atomically precise GNRs have recently been synthesized by on-surface and solution approaches. While on-surface GNRs can be conveniently visualized by scanning tunneling microscopy (STM), and their electronic structure can be probed by scanning tunneling spectroscopy (STS), such characterization remains a great challenge for the solution-synthesized GNRs. Here, we report solution synthesis and detailed STM/STS characterization of atomically precise GNRs with a meandering shape that are structurally related to chevron GNRs but have a reduced energy band gap. The ribbons were synthesized by Ni0-mediated Yamamoto polymerization of specially designed molecular precursors using triflates as the leaving groups and oxidative cyclodehydrogenation of the resulting polymers using Scholl reaction. The ribbons were deposited onto III-V semiconducting InAs(110) substrates by a dry contact transfer technique. High-resolution STM/STS characterization not only confirmed the GNR geometry, but also revealed details of electronic structure including energy states, electronic band gap, as well as the spatial distribution of the local density of states. The experimental STS band gap of GNRs is about 2 eV, which is very close to 2.35 eV predicted by the density functional theory simulations with GW correction, indicating a weak screening effect of InAs(110) substrate. Furthermore, several aspects of GNR-InAs(110) substrate interactions were also probed and analyzed, including GNR tunable transparency, alignment to the substrate, and manipulations of GNR position by the STM tip. The weak interaction between the GNRs and the InAs(110) surface makes InAs(110) an ideal substrate for investigating the intrinsic properties of GNRs. Because of the reduced energy band gap of these ribbons, the GNR thin films exhibit appreciably high electrical conductivity and on/off ratios of about 10 in field-effect transistor measurements, suggesting their promise for device applications.

We studied the electronic band structure and corresponding local density of states of low-index fcc Ag surfaces (100), (110), and (111) by using the empirical tight-binding method in the framework of the Surface Green’s Function Matching formalism. The energy values for different surface and resonance states are reported and a comparison with the available experimental and theoretical data is also done.

Electronic interface properties and the initial growth of hexa-peri-hexabenzocoronene with a borazine core (BN-HBC) on Au(111) have been studied by using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A weak, but non-negligible, interaction between BN-HBC and Au(111) was found at the interface. Both hexa-peri-hexabenzocoronene (HBC) and BN-HBC molecules form well-defined monolayers. The different contrast in STM images of HBC and BN-HBC at different tunneling voltages with submolecular resolution can be ascribed to differences in the local density of states (LDOS). At positive and negative tunneling voltages, STM images reproduce the distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) as determined by density functional theory (DFT) calculations very well.

The electronic spectrum of graphene with a single point impurity is considered. Local densities of states at the impurity site and its nearest neighbors are calculated analytically. Their evolution...

The total electron densities of states for graphene nanoribbons with edges of different chirality, as well as the electron local densities of states for individual atoms in these nanoribbons, are calculated and analyzed. There are sharp resonance peaks near the Fermi level in the total electron densities of states of graphene nanoribbons with zigzag edges, which emerge only in the local densities of atoms from the sublattice that goes directly to the nearest edge (i.e., whose atoms have dangling bonds). Semiconducting gaps appear in the spectra of graphene nanobands with armchair chirality edges having a number of constituent atomic lines that is either a multiple of three, or gives a remainder of one when divided by three. The width of this gap only depends on the width of the nanoribbon, and is the same for all its atoms. The electron spectra of graphene nanoribbons with armchair-chirality edges have a metallic behavior if the number of atomic lines gives a remainder of two when divided by three. However, semiconducting gaps still manifest on the local densities of the atoms belonging to some lines of such nanoribbons.The total electron densities of states for graphene nanoribbons with edges of different chirality, as well as the electron local densities of states for individual atoms in these nanoribbons, are calculated and analyzed. There are sharp resonance peaks near the Fermi level in the total electron densities of states of graphene nanoribbons with zigzag edges, which emerge only in the local densities of atoms from the sublattice that goes directly to the nearest edge (i.e., whose atoms have dangling bonds). Semiconducting gaps appear in the spectra of graphene nanobands with armchair chirality edges having a number of constituent atomic lines that is either a multiple of three, or gives a remainder of one when divided by three. The width of this gap only depends on the width of the nanoribbon, and is the same for all its atoms. The electron spectra of graphene nanoribbons with armchair-chirality edges have a metallic behavior if the number of atomic lines gives a remainder of two when divided by three. Howeve...

Covalent organic frameworks (COFs) are molecule-based 2D and 3D materials that possess a wide range of mechanical and electronic properties. We have performed a joint experimental and theoretical study of the electronic structure of boroxine-linked COFs grown under ultrahigh vacuum conditions and characterized using scanning tunneling spectroscopy on Au(111) and hBN/Cu(111) substrates. Our results show that a single hBN layer electronically decouples the COF from the metallic substrate, thus suppressing substrate-induced broadening and revealing new features in the COF electronic local density of states (LDOS). The resulting sharpening of LDOS features allows us to experimentally determine the COF band gap, bandwidths, and the electronic hopping amplitude between adjacent COF bridge sites. These experimental parameters are consistent with the results of first-principles theoretical predictions.

The tritium release behavior of the Li2TiO3 crystal has become an important index to evaluate its comprehensive performance as a solid breeder material in nuclear fusion reactors. The tritium diffusion on the surface (surface diffusion) and diffusion from the inside to the surface (hopping diffusion) in Li2TiO3 crystals with a 1/3-Li(001) surface are systematically investigated by the first-principles method. Possible adsorption sites, diffusion pathways and energy barriers of surface diffusion and hopping diffusion have been calculated and analyzed, respectively. Tritium atoms are found to diffuse preferentially along the [100] direction on the surface and two equivalent pathways across the surface were identified. The obtained activation energies are about 0.50 eV for surface diffusion and 1.56 eV for hopping diffusion. The local density of states and Bader charge for typical surface diffusion and hopping diffusion pathways are calculated and analyzed. The results reveal that the tritium (T) atom bonds with neighboring oxygen (O) atoms during the surface diffusion, while the T–O interaction is significantly weakened in the hopping diffusion which results in the higher activation energy than that of surface diffusion. In combination with our previous work, a complete tritium diffusion model for the Li2TiO3 crystal is proposed and the corresponding tritium diffusion coefficients are obtained. Our obtained activation energies are in the same range as previous experimental data and could provide theoretical support for the future related experiments.

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2022). = Dissertation, RWTH Aachen University, 2022, The last decades have witnessed the rise of topology, which became one of the dominating paradigms in condensed matter physics. From a theoretical perspective, the focus often lies on topological invariants which, through the bulk-boundary correspondence can be used to predict the presence of edge states at the surfaces of insulating materials. These edge states are believed to be integral in the advancement of future technologies, such as quantum computation, microelectronics and spintronics. This thesis contributes to the field of topological phases of matter by reporting research results concerning the characterization of the latter using two complementary approaches: an energy-resolved, local density of states approach and an energy-unresolved, boundary charge approach. With respect to the first approach, we demonstrate how the local density of states, as computed using the Keldysh Green���s function formalism, can be used to model trans-port experiments in tight-binding models and how to identify topological edge states in the resulting data. As a testbed for this approach we study models of one-dimensional, periodically driven (Floquet) topological insulators and two-dimensional higher order topological superconductors. The findings in this regard are twofold. Firstly, we show how, in the case of the Floquet model, contrary to the local density of states approach, the topological invariants are not able to distinguish between degenerate edge states with vastly different localization lengths, rendering the invariant practically meaning-less. Secondly, while the simulations generally agree with the predictions made using topological considerations, we demonstrate how bulk effects can skew the picture and should therefore be kept in mind when interpreting experimental results. We identify the origin of the aforementioned bulk effects with nontopological edge states, argue for the universality of these states and analytically examine them in the context of the Floquet model and a generalized Kitaev chain, which we identify as the simplest model to feature said states. The second approach to the characterization of topological phases of matter that we discuss is based on the concept of the boundary charge. This experimentally accessible quantity is defined as the charge that accumulates at the surface of an insulator. At zero temperature, it can be thought of as the integrated (up to the chemical potential) excess electronic density, and thus lacks the energy resolution which is essential in detecting the subtle bulk effects mentioned above. Since it generally contains contributions from both localized edge states and extended bulk states, its analysis with respect to the topology of the phase in question is highly nontrivial. We show how the boundary charge can be divided into contributions stemming from bulk states, edge states and from the polarization of the unit cell respectively. We propose novel, boundary charge based invariants, which are given in terms of winding numbers of bulk Green���s functions and which are applicable to all insulating systems, irrespective of symmetry constraints. We demonstrate their validity using randomly generated one-dimensional models. The scope of this thesis lies in the demonstration that the topological invariant approach yields an incomplete picture in certain circumstances, necessitating the use of further theoretical tools, such as those discussed in the following., Published by RWTH Aachen University, Aachen

Metamaterials are composites that are engineered purposefully for realizing electromagnetic characteristics that do not occur naturally in mineral or organic form. These characteristics are realized by regular arrangements of meta atoms, the building blocks of metamaterials, that mimic the atoms in an element. The electric and magnetic responses of these building blocks are engineered in such a way that the effective permittivity and permeability of metamaterials can be tuned. Similarly, the anisotropy of constitutive electromagnetic parameters can also be controlled efficiently. This dissertation focuses on the enhancement of the interaction between light and matter using bulk anisotropic metamaterials and magnetic meta atoms, in order to enhance, control and/or isolate electric and magnetic nature of emitters. This is achieved first through utilization of hyperbolic metamaterials (HMs) which are a subcategory of uniaxially anistotropic materials exhibiting opposite signs of permittivity or permeability along and orthogonal the axis of anisotropy. HMs host a wide spatial spectrum of propagating waves, i.e., high gradient field features can be transferred in HMs owing to the propagating waves in ideally indefinitely large spatial spectrum. Optical HMs are mainly constructed by periodic alternating layers of plasmonic metals and dielectrics. The power emitted by point sources (and arrays of point sources) in the vicinity of HMs is highly boosted compared to regular dielectric media. Moreover, most of the power is absorbed by the HM. Similar characteristics can be realized using graphene layers instead of metals in the infrared regime, where the chemical potential can be an effective means of controlling emission enhancement. Thereafter, a reactively loaded transmission line grid is presented as an example of a two-dimensional HMs, where the canalization of large spectral waves leads to transferring high resolution features. HMs can also be molded into resonators that provide high-quality resonances even in subwavelength dimensions. These extraordinary resonances are demonstrated to boost radiative emission of dipolar emissions. Another exotic property of anisotropic metamaterials is investigated with near-zero permittivity conditions where huge electric field enhancements are achieved in larger intensities than those demonstrated using isotropic near-zero permittivity materials. Lastly, a circular cluster of plasmonic nanospheres under azimuthally polarized vector beams are studied as a way of boosting local magnetic field and isolating it from electric field, which is promising for studying weak magnetic transitions in high frequency range.

Characterizing the many-body localization (MBL) transition in strongly disordered and interacting quantum systems is an important issue in the field of condensed matter physics. We study the single particle Green's functions for a disordered interacting system in one dimension using exact diagnonalization in the infinite temperature limit and provide strong evidence that single particle excitations carry signatures of delocalization to MBL transition. In the delocalized phase, the typical values of the local density of states and the scattering rate are finite while in the MBL phase, the typical values for both the quantities become vanishingly small. The probability distribution functions of the local density of states and the scattering rate are broad log-normal distributions in the delocalized phase while the distributions become very narrow and sharply peaked close to zero in the MBL phase. We also study the eigenstate Green's function for all the many-body eigenstates and demonstrate that both, the energy resolved typical scattering rate and the typical local density of states, can track the many-body mobility edges., Comment: A few changes to the text to improve clarity. No change in results. Close to the published version

This work presents an investigation of carrier transport in $\mathrm{Ga}\mathrm{N}$-based light-emitting diodes in the subthreshold forward-bias regime where tunneling processes are relevant. A quantum kinetic theory of trap-assisted tunneling is developed within the framework of the nonequilibrium Green's function formalism. Based on fully nonlocal scattering self-energies computed in the self-consistent Born approximation and a multiband description of the electronic structure, the model provides access to spectral quantities, such as the local density of states and the current density, which are essential to understand the nature of the tunneling process. The quantum nonradiative recombination rates can be reproduced by the conventional Shockley-Read-Hall theory, provided that the classical charge is replaced with the correct quantum charge, which means that trap-assisted tunneling can be described with drift-diffusion solvers complemented with appropriate quantum corrections for the calculation of the local density of states. The subthreshold $I$-$V$ characteristics and ideality factors predicted by the quantum kinetic model are in agreement with measurements.

We derive a general expression for the electric and magnetic part of the near-field energy density of $N$ dipoles of temperatures ${T}_{1},...,{T}_{N}$ immersed in a background field having a different temperature ${T}_{b}$. In contrast to former expressions this inclusion of the background field allows for determining the energy density of heated or cooled isotropic dipolar objects within an arbitrary environment which is thermalized at a different temperature. Furthermore, we show how the energy density is related to the local density of states. We use this general expression to study the near-field enhanced energy density at the edges and corners of one-dimensional (1D) Su-Schrieffer-Heeger chains and 2D Su-Schrieffer-Heeger lattices of plasmonic InSb nanoparticles when the phase transition from a topological trivial to a topological nontrivial state is made. We discuss the robustness of these modes when adding defects and the possibility to measure the topological edge and corner modes.

Three dimensional photonic crystals offer the possibility to completely inhibit the local density of states (LDOS) for emitters inside the crystal [1] allowing the control of the LDOS which is crucial for emission control, quantum information science, photovoltaics and many more. However, total inhibition is completely true only for crystals of infinite size, whereas real devices are finite. Therefore, it is important to investigate the role of thr position and the dipole orientation of sources inside finite three-dimensional photonic crystals.

The concept of the local density of optical states (widely referred to as "LDOS") is ubiquitous in nanophotonics as it serves to explain a wide range of electromagnetic phenomena, varying from antenna physics [1] , fluorescence [2] - [4] and emission control [5] , [6] , inter-molecular energy transfer [7] , [8] , and strong coupling [9] . Recently, we explored the fundamentals of this concept and its consequences in a broad didactic overview [10] . Here, we focus in greater detail on one of the wide-ranging implications from our study, namely our newly gained insights of how one can view the local density of states in several different ways. Each of these different approaches offers an alternative conceptual insight into the local density of optical states. Importantly, by making a detailed comparison between the different approaches we show the equivalence of rather different research fields, namely electrical engineering, quantum optics, and nanophotonics viewpoints.

The direct measurement of a single emitter decay rate and the simultaneous knowledge of their position is a powerful tool for the study of light-matter interaction at the nanometer scale. In particular, the decay rate is directly related to the local density of states (LDOS) which measures the number of modes of the electromagnetic environment available for the decay of an emitter.

In this study, we use first-principles calculations to investigate the electronic and structural properties of $\text{Mo}{X}_{2}$ $(X=\text{S}, \mathrm{Se}, \mathrm{Te})$ monolayers doped with substitutional Sb atoms, with a central focus on the Sb(Mo) substitution. In ${\mathrm{MoS}}_{2}$, we observe that this substitution is energetically favored under S-rich conditions, where the ${\mathrm{S}}_{2}$ gaseous phase is likely to be present. This result is compatible with a recent experimental observation in Sb-doped ${\mathrm{MoS}}_{2}$ nanosheets grown by chemical vapor deposition. A similar behavior is found in ${\mathrm{MoSe}}_{2}$, but in ${\mathrm{MoTe}}_{2}$ the Sb(Mo) substitution is less likely to occur due to the possible absence of gaseous Te phases in experimental setups. In all cases, several impurity-induced states are found inside the band gap, with energies that span the entire gap. The Fermi energy is pinned a few tenths of eV above the top of the valence band, suggesting a predominant $p$-type behavior, and gap energies are slightly increased in comparison to the pristine systems. The orbital nature of these states is further investigated with projected and local density of states calculations, which reveal similarities to defect states induced by single Mo vacancies as well as their rehybridization with the $5s$ orbital from Sb. Additionally, we find that the band gap of the doped systems is increased in comparison with the pristine materials, in contrast with a previous calculation in Sb-doped ${\mathrm{MoS}}_{2}$ that predicts a gap reduction with a different assignment of valence band and impurity levels. We discuss the similarities, discrepancies, and the limitations of both calculations. We also speculate possible reasons for the experimentally observed redshifts of the $A$ and $B$ excitons in the presence of the Sb dopants in ${\mathrm{MoS}}_{2}$. We hope that these results spark future investigations on other aspects of the problem, particularly those concerning the effects of disorder and electron-hole interaction, and continue to reveal the potential of doped transition-metal dichalcogenides for applications in optoelectronic devices.

In this talk I show how to find materials supporting topological edge states through extending the concept of the refractive index. Rather than compute a topological invariant, we compute the refractive index as a function of propagation direction, finding that zero index in a complex direction corresponds to one-way propagation. As well as providing an alternative viewpoint, we find a circulation dependent local density of states, an optical instance of the Atiyah–Singer index theorem, and a re-interpretation of spin–momentum locking.

The interaction between light and plasmonic structures at the deep-nanometer scale, which is essentially governed by nonclassical effects, has been increasingly investigated by the hydrodynamic model. Several hydrodynamic models have been introduced, in order to describe the motion of the free electron gas in metals. In this work, by employing the hard wall hydrodynamic model (HW-HDM) and the quantum hydrodynamic model (Q-HDM), the nonlocal response of an isolated metallic nanoparticle, excited by a dipole emitter, is investigated. The analysis is performed for the local density of states of an emitter coupled with a spherical nanoparticle, which may be treated analytically. Both radial and tangential emitters are studied, while varying the emitter–nanoparticle separation, and the nanoparticle’s size and material. It is shown that HW-HDM and Q-HDM may generate striking spectral features, which do not arise within the classical approach.

Spontaneous light emission is known to be affected by the local density of states and enhanced when coupled to a resonant cavity. Here, we report on an experimental study of silicon-vacancy (SiV) color center fluorescence and spontaneous Raman scattering from subwavelength diamond particles supporting low-order Mie resonances in the visible range. For the first time to our knowledge, we have measured the size dependences of the SiV fluorescence emission rate and the Raman scattering intensity from individual diamond particles in the range from 200 to 450 nm. The obtained dependences reveal a sequence of peaks, which we explicitly associate with specific multipole resonances. The results are in agreement with our theoretical analysis and highlight the potential of intrinsic optical resonances for developing nanodiamond-based lasers and single-photon sources.