Elementary Electronic Excitations Research Articles

Energy Transport in SiO2 Crystals: Luminescence Excitation Spectra of Stishovite and α-Quartz

Abstract The migration of elementary electronic excitations was studied in a single crystal of stishovite and compared with migration in a crystal of α-quartz and polycrystalline stishovite powder. The research method is based on comparing the transfer of absorbed energy to luminescence centers, used as detectors of quasiparticles, and the near-surface nonradiative annihilation of electronic excitations. A sign of migration is the appearance of some minima in the photoluminescence (PLE) excitation spectrum in the region of maxima in the intrinsic absorption spectrum. The PLE spectrum of stishovite contains the first minimum at 9.8 eV, indicating the migration of electronic excitations and the existence of an intrinsic absorption band in stishovite at 9.8 eV. In α-quartz, the first minimum in the PLE spectrum is located at 10.5 eV and corresponds well to the intrinsic absorption band of the exciton.

Bayesian spectroscopy in solid-state photo-physics

We propose Bayesian spectroscopy (BS) both for the spectral analyses of optical spectra and for normal mode analyses of coherent phonon (CP) signals in solid-state materials. In optical spectra due to elementary electronic excitations, multiple excitonic absorption peaks appear and are overlapped with other background optical transitions, which makes their spectral decomposition difficult. We demonstrate that BS can be used to estimate the band gap and the excitonic binding energies with high accuracies by the introduction of physical laws related with the excitonic transitions. For normal mode analyses of CP signals, we show that BS can estimate the frequency and initial vibrating phase of the normal mode with high accuracies. In contrast to the Fourier transform spectrum which has a broad spectral width on account of the damping behaviors of the CP signals, BS with a physical model of a damped oscillation improves the estimation accuracy of the normal mode frequency by two orders of magnitude compared to the Fourier transform method. These results indicate the significant advantages of BS over conventional methodologies such as the least-squares and Fourier transform methods.

A high-energy-resolution resonant inelastic X-ray scattering spectrometer at ID20 of the European Synchrotron Radiation Facility.

An end-station for resonant inelastic X-ray scattering and (resonant) X-ray emission spectroscopy at beamline ID20 of ESRF - The European Synchrotron is presented. The spectrometer hosts five crystal analysers in Rowland geometry for large solid angle collection and is mounted on a rotatable arm for scattering in both the horizontal and vertical planes. The spectrometer is optimized for high-energy-resolution applications, including partial fluorescence yield or high-energy-resolution fluorescence detected X-ray absorption spectroscopy and the study of elementary electronic excitations in solids. In addition, it can be used for non-resonant inelastic X-ray scattering measurements of valence electron excitations.

Coupling of Elementary Electronic Excitations: Drawing Parallels Between Excitons and Plasmons.

Recent advances in understanding the theoretical and experimental properties of excitons and plasmons have led to several technological breakthroughs. Though emerging from different schools of research, the parallels they possess both in their isolated and assembled forms are indeed interesting. Employing the larger framework of the dipolar coupling model, these aspects are discussed based on the excitonic transitions in chromophores and plasmonic resonances in noble metal nanostructures. The emergence of novel optical properties in linear, parallel, and helical assemblies of chromophores and nanostructures with varying separation distances, orientations, and interaction strengths of interacting dipolar components is discussed. The very high dipolar strengths of plasmonic transitions compared to the excitonic transitions, arising due to the collective nature of the electronic excitations in nanostructures, leads to the emergence of hot spots in plasmonically coupled assemblies. Correlations on the distance dependence of electric field with Raman signal enhancements have paved the way to the development of capillary tube-based plasmonic platforms for the detection of analytes.

Temperature-dependent dispersion model of float zone crystalline silicon

In this paper, we present the temperature dependent dispersion model of float zone crystalline silicon. The theoretical background for valence electronic excitations is introduced in the theoretical part of this paper. This model is based on application of sum rules and parametrization of transition strength functions corresponding to the individual elementary phonon and electronic excitations. The parameters of the model are determined by fitting ellipsometric and spectrophotometric experimental data in the spectral range from far infrared (70cm-1) to extreme ultraviolet (40eV). The ellipsometric data were measured in the temperature range 5–700K. The excitations of the valence electrons to the conduction band are divided into the indirect and direct electronic transitions. The indirect transitions are modeled by truncated Lorentzian terms, whereas the direct transitions are modeled using Gaussian broadened piecewise smooth functions representing 3D and 2D van Hove singularities modified by excitonic effects. Since the experimental data up to high energies (40eV) are available, we are able to determine the value of the effective number of valence electrons. The Tauc–Lorentz dispersion model is used for modeling high energy electron excitations. Two slightly different values of the effective number of valence electrons are obtained for the Jellison–Modine (4.51) and Campi–Coriasso (4.37) parametrization. Our goal is to obtain the model of dielectric response of crystalline silicon which depends only on photon energy, temperature and small number of material parameters, e.g. the concentration of substituted carbon and interstitial oxygen. The model presented in this paper is accurate enough to replace tabulated values of c-Si optical constants used in the optical characterization of thin films diposited on silicon substrates. The spectral dependencies of the optical constants obtained in our work are compared to results obtained by other authors.

Decoherence and relaxation of a single electron in a one-dimensional conductor

We study the decoherence and relaxation of a single elementary electronic excitation propagating in a one-dimensional chiral conductor. Using two-particle interferences in the electronic analog of the Hong-Ou-Mandel experiment, we analyze quantitatively the decoherence scenario of a single electron propagating along a quantum Hall edge channel at filling factor 2. The decoherence results from the emergence of collective neutral excitations induced by Coulomb interaction and leading, in one dimension, to the destruction of the elementary quasiparticle. This study establishes the relevance of electron quantum optics setups to provide stringent tests of strong interaction effects in one-dimensional conductors described by Luttinger liquids paradigm.

Hückel-Hubbard-Ohno modeling of π-bonds in ethene and ethyne with application to trans-polyacetylene.

Quantum chemistry calculations provide the potential energy between two carbon atoms in ethane (H3C-CH3), ethene (H2C[double bond, length as m-dash]CH2), and ethyne (HC[triple bond, length as m-dash]CH) as a function of the atomic distance. Based on the energy function for the σ-bond in ethane, Vσ(r), we use the Hückel model with Hubbard-Ohno interaction for the π electrons to describe the energies Vσπ(r) and Vσππ(r) for the σπ double bond in ethene and the σππ triple bond in ethyne, respectively. The fit of the force functions shows that the electron transfer matrix element and the Peierls coupling can be estimated with some precision whereas the Hubbard-Ohno parameters are insignificant at the distances under consideration. We apply the Hückel-Hubbard-Ohno model to describe the bond lengths and the energies of elementary electronic excitations of trans-polyacetylene, (CH)n, whereby we adjust the σ-bond potential for conjugated polymers.

ChemInform Abstract: Hot‐Electron‐Mediated Surface Chemistry: Toward Electronic Control of Catalytic Activity

AbstractReview: 62 refs.

Hot-Electron-Mediated Surface Chemistry: Toward Electronic Control of Catalytic Activity

Energy dissipation at surfaces and interfaces is mediated by excitation of elementary processes, including phonons and electronic excitation, once external energy is deposited to the surface during exothermic chemical processes. Nonadiabatic electronic excitation in exothermic catalytic reactions results in the flow of energetic electrons with an energy of 1-3 eV when chemical energy is converted to electron flow on a short (femtosecond) time scale before atomic vibration adiabatically dissipates the energy (in picoseconds). These energetic electrons that are not in thermal equilibrium with the metal atoms are called "hot electrons". The detection of hot electron flow under atomic or molecular processes and understanding its role in chemical reactions have been major topics in surface chemistry. Recent studies have demonstrated electronic excitation produced during atomic or molecular processes on surfaces, and the influence of hot electrons on atomic and molecular processes. We outline research efforts aimed at identification of the intrinsic relation between the flow of hot electrons and catalytic reactions. We show various strategies for detection and use of hot electrons generated by the energy dissipation processes in surface chemical reactions and photon absorption. A Schottky barrier localized at the metal-oxide interface of either catalytic nanodiodes or hybrid nanocatalysts allows hot electrons to irreversibly transport through the interface. We show that the chemicurrent, composed of hot electrons excited by the surface reaction of CO oxidation or hydrogen oxidation, correlates well with the turnover rate measured separately by gas chromatography. Furthermore, we show that hot electron flows generated on a gold thin film by photon absorption (or internal photoemission) can be amplified by localized surface plasmon resonance. The influence of hot charge carriers on the chemistry at the metal-oxide interface are discussed for the cases of Au, Ag, and Pt nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts.

Composite Operator Method Analysis of the Underdoped Cuprates Puzzle

The microscopical analysis of the unconventional and puzzling physics of the underdoped cuprates, as carried out lately by means of the composite operator method (COM) applied to the 2D Hubbard model, is reviewed and systematized. The 2D Hubbard model has been adopted as it has been considered the minimal model capable of describing the most peculiar features of cuprates held responsible for their anomalous behavior. COM is designed to endorse, since its foundation, the systematic emergence in any SCS of new elementary excitations described by composite operators obeying noncanonical algebras. In this case (underdoped cuprates—2D Hubbard model), the residual interactions—beyond a 2-pole approximation—between the new elementary electronic excitations, dictated by the strong local Coulomb repulsion and well described by the two Hubbard composite operators, have been treated within the noncrossing approximation. Given this recipe and exploiting the few unknowns to enforce the Pauli principle content in the solution, it is possible to qualitatively describe some of the anomalous features of high-Tc cuprate superconductors such as large versus small Fermi surface dichotomy, Fermi surface deconstruction (appearance of Fermi arcs), nodal versus antinodal physics, pseudogap(s), and kinks in the electronic dispersion. The resulting scenario envisages a smooth crossover between an ordinary weakly interacting metal sustaining weak, short-range antiferromagnetic correlations in the overdoped regime to an unconventional poor metal characterized by very strong, long-but-finite-range antiferromagnetic correlations leading to momentum-selective non-Fermi liquid features as well as to the opening of a pseudogap and to the striking differences between the nodal and the antinodal dynamics in the underdoped regime.

Inelastic electron and Raman scattering from the collective excitations in quantum wires: Zero magnetic field

The nanofabrication technology has taught us that an m-dimensional confining potential imposed upon an n-dimensional electron gas paves the way to a quasi-(n-m)-dimensional electron gas, with m ⩽n and 1 ⩽ n, m ⩽ 3. This is the road to the(semiconducting) quasi-n dimensional electron gas systems we have been happily traversing on now for almost two decades. Achieving quasi-one dimensional electron gas (Q-1DEG) [or quantum wire(s) for more practical purposes] led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A realistic Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. In the language of condensed matter physics, a critical scrutiny of Q-1DEG systems has provided us with a host of exotic(electronic, optical, and transport) phenomena unseen in their higher- or lower-dimensional counterparts. This has motivated us to undertake a systematic investigation of the inelastic electron scattering (IES) and the inelastic light scattering(ILS) from the elementary electronic excitations in quantum wires. We begin with the Kubo's correlation functions to derive the generalized dielectric function, the inverse dielectric function,and the Dyson equation for the dynamic screened potential in the framework of Bohm-Pines’random-phase approximation. These fundamental tools then lead us to develop methodically the theory of IES and ILS for the Q-1DEG systems. As an application of the general formal results, which know no bounds regarding the subband occupancy, we compute the density of states, the Fermi energy, the full excitation spectrum[comprised of intrasubband and intersubband single-particle as well as collective excitations], the loss functions for the IES and the Raman intensity for the ILS. We observe that it is the collective (plasmon)excitations that largely contribute to the predominant peaks in the energy-loss and the Raman spectra. The inductive reasoning is that the IES can be a potential alternative of the overused ILS for investigating collective excitations in quantum wires. We trust that this research work shall be useful to all – from novice to expert and from theorist to experimentalist – who believe in the power of traditional science.

Optical dielectric function of gold

In metal optics gold assumes a special status because of its practical importance in optoelectronic and nano-optical devices, and its role as a model system for the study of the elementary electronic excitations that underlie the interaction of electromagnetic fields with metals. However, largely inconsistent values for the frequency dependence of the dielectric function describing the optical response of gold are found in the literature. We performed precise spectroscopic ellipsometry measurements on evaporated gold, template-stripped gold, and single-crystal gold to determine the optical dielectric function across a broad spectral range from 300 nm to 25 $\ensuremath{\mu}$m (0.05--4.14 eV) with high spectral resolution. We fit the data to the Drude free-electron model, with an electron relaxation time ${\ensuremath{\tau}}_{D}=14\ifmmode\pm\else\textpm\fi{}3$ fs and plasma energy $\ensuremath{\hbar}{\ensuremath{\omega}}_{p}=8.45$ eV. We find that the variation in dielectric functions for the different types of samples is small compared to the range of values reported in the literature. Our values, however, are comparable to the aggregate mean of the collection of previous measurements from over the past six decades. This suggests that although some variation can be attributed to surface morphology, the past measurements using different approaches seem to have been plagued more by systematic errors than previously assumed.

Inelastic electron and light scattering from the elementary electronic excitations in quantum wells: Zero magnetic field

The most fundamental approach to an understanding of electronic, optical, and transport phenomena which the condensed matter physics (of conventional as well as nonconventional systems) offers is generally founded on two experiments: the inelastic electron scattering and the inelastic light scattering. This work embarks on providing a systematic framework for the theory of inelastic electron scattering and of inelastic light scattering from the electronic excitations in GaAs/Ga1−xAlxAs quantum wells. To this end, we start with the Kubo's correlation function to derive the generalized nonlocal, dynamic dielectric function, and the inverse dielectric function within the framework of Bohm-Pines’ random-phase approximation. This is followed by a thorough development of the theory of inelastic electron scattering and of inelastic light scattering. The methodological part is then subjected to the analytical diagnoses which allow us to sense the subtlety of the analytical results and the importance of their applications. The general analytical results, which know no bounds regarding, e.g., the subband occupancy, are then specified so as to make them applicable to practicality. After trying and testing the eigenfunctions, we compute the density of states, the Fermi energy, the full excitation spectrum made up of intrasubband and intersubband – single-particle and collective (plasmon) – excitations, the loss functions for all the principal geometries envisioned for the inelastic electron scattering, and the Raman intensity, which provides a measure of the real transitions induced by the (laser) probe, for the inelastic light scattering. It is found that the dominant contribution to both the loss peaks and the Raman peaks comes from the collective (plasmon) excitations. As to the single-particle peaks, the analysis indicates a long-lasting lack of quantitative comparison between theory and experiments. It is inferred that the inelastic electron scattering can be a potential alternative of the inelastic light scattering for investigating elementary electronic excitations in quantum wells.

Terahertz plasmon and infrared coupled plasmon–phonon modes in graphene

Plasmon and coupled plasmon–phonon modes of Dirac particles in graphene are investigated theoretically within the diagrammatic self-consistent field theory. It shows that two terahertz plasmon modes and four infrared coupled plasmon–phonon modes can be achieved via intra- and inter-band transitions in graphene. We find that with increasing q and carrier density, the plasmon modes are strongly coupled with optic-phonon modes in graphene in the infrared region. The coupled plasmon–phonon modes exhibit some interesting features which can be utilized to realize the plasmonic devices. Our results suggest that the carrier–phonon interaction should be considered to understand and explain the properties of elementary electronic excitations in graphene.

Electron Quantum Optics: Partitioning Electrons One by One

We have realized a quantum optics like Hanbury Brown-Twiss (HBT) experiment by partitioning, on an electronic beam splitter, single elementary electronic excitations produced one by one by an on-demand emitter. We show that the measurement of the output currents correlations in the HBT geometry provides a direct counting, at the single charge level, of the elementary excitations (electron-hole pairs) generated by the emitter at each cycle. We observe the antibunching of low energy excitations emitted by the source with thermal excitations of the Fermi sea already present in the input leads of the splitter, which suppresses their contribution to the partition noise. This effect is used to probe the energy distribution of the emitted wave packets.

Single-particle and collective excitations in quantum wires made up of vertically stacked quantum dots: Zero magnetic field

We report on the theoretical investigation of the elementary electronic excitations in a quantum wire made up of vertically stacked self-assembled InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the experimental setups prompt us to consider an infinitely periodic system of two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers. The resultant quantum wire is characterized by a two-dimensional harmonic confining potential in the x-y plane and a periodic (Kronig-Penney) potential along the z (or the growth) direction within the tight-binding approximation. Since the wells and barriers are formed from two different materials, we employ the Bastard's boundary conditions in order to determine the eigenfunctions along the z direction. These wave functions are then used to generate the Wannier functions, which, in turn, constitute the legitimate Bloch functions that govern the electron dynamics along the direction of periodicity. Thus, the Bloch functions and the Hermite functions together characterize the whole system. We then make use of the Bohm-Pines' (full) random-phase approximation in order to derive a general nonlocal, dynamic dielectric function. Thus, developed theoretical framework is then specified to work within a (lowest miniband and) two-subband model that enables us to scrutinize the single-particle as well as collective responses of the system. We compute and discuss the behavior of the eigenfunctions, band-widths, density of states, Fermi energy, single-particle and collective excitations, and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier- and well-widths can allow us to tailor the excitation spectrum in the desired energy range. Given the advantage of the vertically stacked quantum dots over the planar ones and the foreseen applications in the single-electron devices and in the quantum computation, it is quite interesting and important to explore the electronic, optical, and transport phenomena in such systems.

Spectroscopic characterization of actinide materials

Advanced spectroscopic techniques provide new and unique tools for unraveling the nature of the electronic structure of actinide materials. Inelastic neutron scattering experiments, which address temporal aspects of lattice and magnetic fluctuations, probe electromagnetic multipole interactions and the coupling between electronic and vibrational degrees of freedom. Nuclear magnetic resonance clearly demonstrates different magnetic ground states at low temperature. Photoemission spectroscopy provides information on the occupied part of the electronic density of states and has been used to investigate the momentum-resolved electronic structure and the topology of the Fermi surface in a variety of actinide compounds. Furthermore, x-ray absorption and electron energy-loss spectroscopy have been used to probe the relativistic nature, occupation number, and degree of localization of 5f electrons across the actinide series. More recently, element- and edge-specific resonant and non-resonant inelastic x-ray scattering experiments have provided the opportunity of measuring elementary electronic excitations with higher resolution than traditional absorption techniques. Here, we will discuss results from these spectroscopic techniques and what they tell us of the electronic and magnetic properties of selected actinide materials.

Intra- and intersite electronic excitations in multiferroicTbMnO3probed by resonant inelastic x-ray scattering

$\text{Mn}\text{ }3d$ valence states and elementary electronic excitations in single-crystalline ${\text{TbMnO}}_{3}$ were probed with resonant inelastic x-ray scattering (RIXS) (or resonant x-ray emission spectroscopy, RXES), polarized x-ray absorption spectra and ab initio electron-structure calculations. Polarized $\text{Mn}\text{ }K$-edge x-ray absorption spectra of ${\text{TbMnO}}_{3}$ crystals exhibit a significant anisotropy along three crystallographic directions, particularly for the white-line region. The $1s3p$-RXES spectra obtained at the $\text{Mn}\text{ }K$ edge reveal that the quadrupolar Raman regime is restricted predominantly to below the pre-edge peak whereas the fluorescence regime starts from the first pre-edge peak of $1s\ensuremath{\rightarrow}3d$ transitions, indicating a relatively delocalized character of unoccupied $\text{Mn}\text{ }3d$ states. The additional $\text{K}\ensuremath{\beta}$ emission profile at energy loss $\ensuremath{\sim}62\text{ }\text{eV}$ is attributed to the off-site dipole $\text{Mn}\text{ }1s{\text{-Mn}}^{\ensuremath{'}}\text{ }3d$ and/or $\text{Mn}\text{ }1s\text{-Tb}\text{ }5d$ transitions, originating from hybridization between $\text{Mn}\text{ }4p$ states and neighboring ${\text{Mn}}^{\ensuremath{'}}\text{ }3d/\text{Tb}\text{ }5d$ states. The off-site dipole transition makes a considerable contribution to the pre-edge region of $\text{Mn}\text{ }K$-edge spectrum. Three prominent RIXS features at $\ensuremath{\sim}2.9$, 7, and 11 eV were observed. Based on $\text{GGA}+U$ calculations, the 7 eV region corresponds to transitions from $\text{O}\text{ }2p$ states to unoccupied minority $\text{Mn}\text{ }3d$ states, whereas the 11 eV band is ascribed to transitions from the $\text{O}\text{ }2p$ band to the empty $\text{Tb}\text{ }5d$ band. The broad 2.9 eV band is attributed to the coexistence of on-site $\text{Mn}\text{ }3d\text{-Mn}\text{ }3d$ and off-site $\text{Mn}\text{ }3d{\text{-Mn}}^{\ensuremath{'}}\text{ }3d$ transitions.

109 Expression and activation of protein kinases in Triple Negative Breast Cancer (TNBC)

We investigate InAs self-assembled quantum dots (SAQD) by resonant inelastic light scattering. By applying a gate voltage between a metallic front gate and a back electrode, we can charge the quantum dots with single electrons (1–6). With resonant inelastic light scattering, we can directly observe the elementary electronic excitations of the few-electron quantum-dot atoms, which are formed by the SAQD. We observe excitations which we identify as transitions of electrons from the s- to the p-shell (s–p transitions) and from the p- to the d-shell (p–d transitions) of the quasiatoms. We find that the s–p transition energy decreases when the p-shell is filled with 1–4 electrons. This can be explained as an effect of Coulomb interaction, which is confirmed by calculations of the few-electron system, using exact numerical diagonalization.

1109 Direct cell entry of gold/iron-oxide magnetic nanoparticles in adenovirus mediated gene delivery

We investigate InAs self-assembled quantum dots (SAQD) by resonant inelastic light scattering. By applying a gate voltage between a metallic front gate and a back electrode, we can charge the quantum dots with single electrons (1–6). With resonant inelastic light scattering, we can directly observe the elementary electronic excitations of the few-electron quantum-dot atoms, which are formed by the SAQD. We observe excitations which we identify as transitions of electrons from the s- to the p-shell (s–p transitions) and from the p- to the d-shell (p–d transitions) of the quasiatoms. We find that the s–p transition energy decreases when the p-shell is filled with 1–4 electrons. This can be explained as an effect of Coulomb interaction, which is confirmed by calculations of the few-electron system, using exact numerical diagonalization.