Quasi-free Electrons Research Articles

Inelastic resonant scattering of electrons on hydrogen-like ions

Abstract The inelastic electron scattering is one of the processes that must be understood in detail for the correct interpretation of astrophysical data. We suggest ab initio QED treatment of the inelastic scattering of quasi-free electrons on hydrogen-like ions with possible formation and subsequent decay of intermediate autoionizing states. We calculate the doubly differential cross sections for scattering on F8+, Ca19+ and Kr35+ in the range of energies where doubly excited 3 l 3 l ′ states are involved. The energies and widths of these states are presented.

Electron Attachment to the Nucleobase Uracil in Diethylene Glycol: The Signature of a Doorway.

The cellular environment plays a significant role in low energy electron-mediated radiation damage to genetic materials. In this study, we have modeled the effect of the bulk medium on electron attachment to nucleobases in diethylene glycol (DEG) using uracil as a test case, in accordance with recent experimental work on the observation of dissociative quasi-free electron attachment to nucleoside via excited anion radical in solution (in DEG). Our EOM-CCSD-based quantum mechanical/molecular mechanical (QM/MM) simulations indicate that the electron scavenging by uracil in DEG is much slower than that observed in the aqueous medium due to its viscosity. This work also establishes that a doorway mechanism exists in uracil microsolvated and bulk solvated with DEG, with the dipole-bound state and solvent-bound state acting as doorway states, respectively.

Consciousness: a quantum optical effect in fluorescent protein pathways

This paper presents a physical mechanism of embodied consciousness based on the dynamic organicity theory. We use the entropic pilot wave theory to describe the quantum dipole oscillations from dipole-bound delocalized (quasi-free) electrons in nonpolar nanocavities of aromatic amino acid residues (benzene moiety /cyclic hydrocarbons that contain resonance structures) and their fluorescent pathways. These pathways contain cavity quasipolariton condensates composed of quantized polarization waves of entangled photons. The behavior of oscillating molecular dipoles is influenced by the quantum nature of dynamic organicity, which causes energy fluctuations necessary to move delocalized electrons and create bare polaritons (quantized polarization waves). These waves correspond to photon quasiparticles interacting with water molecules to form quasipolaritons, softened by interacting with hydroxide ions (OH-) within crystal lattices of interfacial water H30. When [H3O+]=[OH−], the solution is neutral in hydrophobic nanocavities. In such nonpolar cavities, evanescent photons (non-radiative transitions in the absence of any source) are emitted while protons (H+) diffuse due to recombination with hydroxide (OH-) ions, acting as protonic analogs of ‘holes’ or excitons. In protein pores, proton motion strongly coupled with π-electron delocalization is a conduit for exciton-photon (polariton) and its polarization wave component. Internal energy fluctuations comprise both quantum potential energy and negative quantum kinetic energy. We explore how quantum potential energy influences the negentropic effect of a 'repulsive force' guided by entropic pilot waves through pilot wave force (negentropic force), functioning as an information-based action of the polarization wave as a conduit of the cavity quasipolariton. When the rate of change of quantum entropy is zero, and momentum of the polarization wave is zero the internal energy transduction between quantum potential energy to quantum kinetic energy manifests as the negentropic force and facilitates the movement of information-based action for information encoding when negative quantum kinetic energy happens at certain times. Experiments have shown that biphoton entanglement interferes with anaesthetics. We postulate that the disruption of cavity polaritonic condensate through its polarization wave component disrupts the decoding of information, suggesting consciousness is attributed to a quantum optical effect. Therefore, we further theorize that consciousness is attributed to the negative quantum kinetic energy of the polarization wave, which provides an informational structure of multiscale redundancy when negentropic action reduces information redundancy. This has profound implications for understanding consciousness as nonmechanical action channeled through negentropic force when the rate of change of quantum entropy is zero.

Fermi Rubik’s Cube in High-Pressure Induced Chlorine-Rich Compounds

Abstract In the quasi-free electron model, the Fermi surface spreads into a sphere in the Brillouin zone, i.e., the Fermi sphere. The Fermi sphere exists widely in metal systems, no matter whether the crystal is in a body-center cubic, face-center cubic, or hexagonal close-packed lattice. Here, we report a class of compounds stabilized at high pressure with Rubik’s cubic Fermi surface, in which the representative example is P m 3 ¯ n -CaCl3. Our quantum-mechanical variable-composition evolutionary simulations predict the thermal stabilities of CaCl3, and the tight-binding model reveals that its unique Fermi surface originates from the quasi-one-dimensional interaction, structural symmetric protection, and particle-hole symmetry breaking. Furthermore, by its flat and steep band structure, CaCl3 has a huge span of effective mass from 9.08 × 103 m e (super-heavy) to 5.13 × 10−4 m e on the Fermi level, which supplies an interesting platform for quasiparticle research.

Ultrafast Heating-Induced Suppression of d-Band Dominance in the Electronic Excitation Spectrum of Cuprum.

The combination of isochoric heating of solids by free-electron lasers (FELs) and in situ diagnostics by X-ray Thomson scattering (XRTS) allows for measurements of material properties at warm dense matter (WDM) conditions relevant for astrophysics, inertial confinement fusion, and materials science. In the case of metals, the FEL beam pumps energy directly into electrons with the lattice structure of ions being nearly unaffected. This leads to a unique transient state that gives rise to a set of interesting physical effects, which can serve as a reliable testing platform for WDM theories. In this work, we present extensive linear-response time-dependent density functional theory (TDDFT) results for the electronic dynamic structure factor of isochorically heated copper with a face-centered cubic lattice. At ambient conditions, the plasmon is heavily damped due to the presence of d-band excitations, and its position is independent of the wavenumber. In contrast, the plasmon feature starts to dominate the excitation spectrum and has a Bohm-Gross-type plasmon dispersion for temperatures T ≥ 4 eV, where the quasi-free electrons in the interstitial region are in the WDM regime. In addition, we analyze the thermal changes in the d-band excitations and outline the possibility to use future XRTS measurements of isochorically heated copper as a controlled testbed for WDM theories.

Reactivity of quasi-free electrons toward N3- and its impact on H2 formation mechanism in water radiolysis.

Picosecond pulse radiolysis measurements were employed to assess the effectiveness of N3- in scavenging quasi-free electrons in aqueous solutions. The absorption spectra of hydrated electrons were recorded within a 100 ps timeframe across four distinct solutions with N3- concentrations of 0.5, 1, 2, and 5 M in water. The results revealed a concentration-dependent shift in the maximum absorption spectra of fully solvated electrons. Notably, at 5 M concentration, the maximum absorption occurred at 670 nm, in contrast to 715 nm observed for water. Intriguingly, the formation yield of hydrated electrons within the initial 5 ps electron pulse remained unaffected, showing that, even at a concentration of 5 M, N3- does not effectively scavenge quasi-free electrons. This is in disagreement with conclusions from stochastic models found in the literature. This observation has an important impact on understanding the mechanism of H2 formation in water radiolysis, which we discuss briefly here.

О генерации электрического разряда в диэлектрике потоком фотонов

The development of an electric discharge during photon scattering in a dielectric material is considered. A preliminary mathematical model of the discharge process is presented. The model is based on a quantum kinetic equation for quasi-free charge carriers produced by bulk radiation effects and impact ionization. Equations are obtained for the concentration, drift current density, and gas temperature of quasi-free electrons. A test example is considered, confirming that the model does not contradict the known conditions for the formation of an electric discharge.

Time-domain modeling of interband transitions in plasmonic systems

Efficient modeling of dispersive materials via time-domain simulations of the Maxwell equations relies on the technique of auxiliary differential equations. In this approach, a material’s frequency-dependent permittivity is represented via a sum of rational functions, e.g., Lorentz poles, and the associated free parameters are determined by fitting to experimental data. In the present work, we present a modified approach for plasmonic materials that requires considerably fewer fit parameters than traditional approaches. Specifically, we consider the underlying microscopic theory and, in the frequency domain, separate the hydrodynamic contributions of the quasi-free electrons in partially filled bands from the interband transitions. As an illustration, we apply our approach to gold and demonstrate how to treat the interband transitions within the effective model via connecting to the underlying electronic band structure, thereby assigning physical meaning to the remaining fit parameters. Finally, we show how to utilize this approach within the technique of auxiliary differential equations. Our approach can be extended to other plasmonic materials and leads to efficient time-domain simulations of plasmonic structures for frequency ranges where interband transitions have to be considered.

Electron thermalization length in solid para-hydrogen at low-temperature.

We report the first ever measurements of the thermalization length of low-energy electrons injected into solid para-hydrogen at a temperature T ≈ 2.8 K. The use of the pulsed Townsend photoinjection technique has allowed us to investigate the behavior of quasi-free electrons rather than of massive, slow negative charges, as reported in all previous literature. We have found an average thermalization length ⟨z0⟩ = 26.1 nm, which is three to five times longer than that in liquid helium at the same temperature.

Validation of the Heuristic Model for the Mobility of Quasi-Free Electrons in Dense Helium Gas

Validation of the Heuristic Model for the Mobility of Quasi-Free Electrons in Dense Helium Gas

Engineering quantum states and electronic landscapes through surface molecular nanoarchitectures

Surfaces are at the frontier of every known solid. They provide versatile supports for functional nanostructures and mediate essential physicochemical processes. Being intimately related with 2D materials, interfaces and atomically thin films often feature distinct electronic states with respect to the bulk, which are key for many relevant properties, such as catalytic activity, interfacial charge-transfer, or crystal growth mechanisms. Of particular interest is reducing the surface electrons' dimensionality and spread with atomic precision, to induce novel quantum properties via lateral scattering and confinement. Both atomic manipulation and supramolecular principles provide access to custom-designed molecular superlattices, which tailor the surface electronic landscape and influence fundamental chemical and physical properties at the nanoscale. Herein, we review the confinement of surface state electrons focusing on their interaction with molecule-based scaffolds created by molecular manipulation and self-assembly protocols under ultrahigh vacuum conditions. Starting from the quasi-free 2D electron gas present at the (111)-terminated surface planes of noble metals, we illustrate the enhanced molecule-based structural complexity and versatility compared to simple atoms. We survey low-dimensional confining structures in the form of artificial lattices, molecular nanogratings or quantum dot arrays, which are constructed upon appropriate choice of their building constituents. Whenever the realized (metal-)organic networks exhibit long-range order, modified surface band structures with characteristic features emerge, revealing intriguing physical properties, such as discretization, quantum coupling or energy and effective mass renormalization. Such collective electronic states can be additionally modified by positioning guest species at the voids of open nanoarchitectures [...].

High-Performance Room-Temperature NO2 Gas Sensor Based on Au-Loaded SnO2 Nanowires under UV Light Activation.

Optical excitation is widely acknowledged as one of the most effective means of balancing sensor responses and response/recovery properties at room temperature (RT, 25 °C). Moreover, noble metals have been proven to be suitable as photosensitizers for optical excitation. Localized surface plasmon resonance (LSPR) determines the liberalization of quasi-free electrons in noble metals under light irradiation, and numerous injected electrons in semiconductors will greatly promote the generation of chemisorbed oxygen, thus elevating the sensor response. In this study, pure SnO2 and Au/SnO2 nanowires (NWs) were successfully synthesized through the electrospinning method and validated using XRD, EDS, HRTEM, and XPS. Although a Schottky barrier led to a much higher initial resistance of the Au/SnO2 composite compared with pure SnO2 at RT in the dark, the photoinduced resistance of the Au/SnO2 composite became lower than that of pure SnO2 under UV irradiation with the same intensity, which confirmed the effect of LSPR. Furthermore, when used as sensing materials, a detailed comparison between the sensing properties of pure SnO2 and Au/SnO2 composite toward NO2 in the dark and under UV irradiation highlighted the crucial role of the LSPR effects. In particular, the response of Au/SnO2 NWs toward 5 ppm NO2 could reach 65 at RT under UV irradiation, and the response/recovery time was only 82/42 s, which far exceeded those under Au modification-only or optical excitation-only. Finally, the gas-sensing mechanism corresponding to the change in sensor performance in each case was systematically proposed.

Search for Spontaneous Radiation from Wave Function Collapse in the Majorana Demonstrator.

The Majorana Demonstrator neutrinoless double-beta decay experiment comprises a 44kg (30kg enriched in ^{76}Ge) array of p-type, point-contact germanium detectors. With its unprecedented energy resolution and ultralow backgrounds, Majorana also searches for rare event signatures from beyond standard model physics in the low energy region below 100keV. In this Letter, we test the continuous spontaneous localization (CSL) model, one of the mathematically well-motivated wave function collapse models aimed at solving the long-standing unresolved quantum mechanical measurement problem. While the CSL predicts the existence of a detectable radiation signature in the x-ray domain, we find no evidence of such radiation in the 19-100keV range in a 37.5kg-y enriched germanium exposure collected between December 31, 2015, and November 27, 2019, with the Demonstrator. We explored both the non-mass-proportional (n-m-p) and the mass-proportional (m-p) versions of the CSL with two different assumptions: that only the quasifree electrons can emit the x-ray radiation and that the nucleus can coherently emit an amplified radiation. In all cases, we set the most stringent upper limit to date for the white CSL model on the collapse rate, λ, providing a factor of 40-100 improvement in sensitivity over comparable searches. Our limit is the most stringent for large parts of the allowed parameter space. If the result is interpreted in terms of the Diòsi-Penrose gravitational wave function collapse model, the lower bound with a 95%confidence level is almost an order of magnitude improvement over the previous best limit.

Magneto-optic Kerr effect in Gd20Co80 alloy

The magneto-optical Kerr effect in Gd20Co80 alloy and cobalt thin films has been studied in a broad spectral range applying spectral ellipsometry experimental technique. The results of the experiments showed the complex nature of the complex Kerr angle dispersion curves. A quantum mechanical formalism for degenerate and non-degenerate Landau levels for quasi-free electrons in ferromagnetic material has been developed in order to analyze the experimental data. The equivalence of relations for off-diagonal dielectric tensor elements for non-degenerate Landau levels to the classical case of the motion of quasi-free electrons along circular trajectories in a magnetic field has been theoretically shown. The degenerate Landau levels in this approach are the result of motion of electrons in small confined volumes near rare-earth alloy atoms. Rotation of light polarization occurs in this case due to transitions between subbands having different magnetic quantum numbers. This theoretical approach allowed us to interpret in detail shapes and sign of the complex Kerr angle dispersion curves, which actually include the contributions of optical transitions between degenerate and non-degenerate energy levels. The complex Kerr angle sign is determined by the magnetization magnetic field direction for non-degenerate Landau levels and the Hund rule for degenerate Landau levels.

Features of the radiative properties of quantum-size particles of narrow-gap semiconductors

For colloidal quantum-size particles (QP) of narrow-gap semiconductors, in contrast to quantum dots of wide-gap CdSe, in QP-PbS there take place an anomalous temperature dependence of the photoluminescence intensity. Also, in the planar microstructure containing QP-InSb, long-wavelength radiation (more than 3 μm) and photoconductivity (over 20 μm) was observed. Under certain conditions, the radiation intensity and photoconductivity demonstrate a resonance maximum. The effects were explained in the model of a one-dimensional quantum oscillator, which energy substantially depends on the effective mass of its quasi-free electron. This leads to competition between the manifestations of long-wave radiation and photoluminescence, and hence, to the anomalous temperature dependence of photoluminescence. It is assumed that QP-InSb in a planar microstructure can be sources and receivers of terahertz radiation, which properties depend on the crystal structure of quantum-sized particles determined by the parameters of their synthesis. Keywords: quantum-dimensional particle, quantum dot, narrow-gap semiconductor, effective mass, Brillouin zone, dimensional quantization, quantum oscillator, photoluminescence, long-wavelength radiation.

Observation of the ponderomotive effect in non-valence bound states of polyatomic molecular anions

The ponderomotive force on molecular systems has rarely been observed hitherto, despite potentially being extremely useful for the manipulation of the molecular properties. Here, the ponderomotive effect in the non-valence bound states has been experimentally demonstrated, for the first time to the best of our knowledge, giving great promise for the manipulation of polyatomic molecules by the dynamic Stark effect. Entire quantum levels of the dipole-bound state (DBS) and quadrupole-bound state (QBS) of the phenoxide (or 4-bromophenoxide) and 4-cyanophenoxide anions, respectively, show clear-cut ponderomotive blue-shifts in the presence of the spatiotemporally overlapped non-resonant picosecond control laser pulse. The quasi-free electron in the QBS is found to be more vulnerable to the external oscillating electromagnetic field compared to that in the DBS, suggesting that the non-valence orbital of the former is more diffusive and thus more polarizable compared to that of the latter.

Plasma reflectivity behavior under strong subpicosecond excitation of liquids

Emerging laser plasma-based technologies require new knowledge on the optical pump optimization and underlying physics of laser–matter interaction. Plasma in liquid jets is still largely unexplored, although this configuration is actively used as a part of optical devices. Hereby, in this work, we report on the reflectivity-based approach to study the optical properties of the induced plasma and quasi-free electron temporal dynamics. The single-shot experiments provide plasma characteristics relative to the laser pump parameters. A strong angular dependence of the plasma absorptivity, which affects rigorously the reflectivity curve, is demonstrated. Furthermore, twofold higher plasma reflectivity in ethanol is revealed and explained through the theoretical model of ultrashort laser pulse interaction with a thin dielectric surface layer. Finally, the time-resolved fundamental and third harmonic reflection measurements and associated analytical study provide the new insight into the electron density dynamics in the case of optical breakdown in water and ethanol. We believe that these findings are of particular significance for the development of highly efficient plasma-based x rays and THz radiation sources.

Anomalous two-photon Compton scattering

X-ray free-electron lasers can generate radiation pulses with extreme peak intensities at short wavelengths. This enables the investigation of laser–matter interactions in a regime of high fields, yet at a non-relativistic ponderomotive potential, where ordinary rules of light–matter interaction may no longer apply and nonlinear processes are starting to become observable. Despite small cross-sections, first nonlinear effects in the hard x-ray regime have recently been observed in solid targets, including x-ray-optical sum-frequency generation (XSFG), x-ray second harmonic generation (XSHG) and two-photon Compton scattering (2PCS). Nonlinear interactions of bound electrons in the x-ray range are fundamentally different from those dominating at optical frequencies. Whereas in the optical regime nonlinearities are predominantly caused by anharmonicities of the atomic potential in the chemical bonds, x-ray nonlinearities far above atomic resonances are expected to be due to nonlinear oscillations of quasi-free electrons, including inner-shell atomic electrons. While the quasi-free-electron model agrees reasonably well with the experimental data for XSFG and XSHG, 2PCS measurements have led to unexpected results: the energy of the nonlinearly scattered photons from non-relativistic electrons shows a substantial unexpected red shift in addition to the Compton shift that is well beyond that predicted by a nonlinear quantum electrodynamics model for free electrons.A potential explanation for the spectral broadening is based on a previously unexplored scattering process that involves the whole atom rather than just quasi-free electrons. A first simulation that includes the atomic binding potential was successful in describing a broadening of the spectrum of the nonlinearly scattered photons to longer wavelengths for soft x-rays. However, the same model does not show any broadening at hard x-ray wavelengths, which is in agreement with other simulation approaches. To this point no calculation has been able to reproduce the experimentally observed broadening.Here we present further experimental data of 2PCS for an extended parameter range using additional diagnostics. In particular, we present measurements of the electron momentum distribution during the interaction that strongly suggest that the spectral broadening is not caused by an increased plasma temperature. We extend our measurement of the magnitude of the red shift in beryllium to in addition to the Compton shift expected for free electrons and expand the measurement of the angular distribution to include forward scattering angles. We also present first measurements of 2PCS from diamond.

Quasi-Free Electron-Mediated Radiation Sensitization by C5-Halopyrimidines.

Substitution of the thymidine moiety in DNA by C5-substituted halogenated thymidine analogues causes significant augmentation of radiation damage in living cells. However, the molecular pathway involved in such radiosensitization process has not been clearly elucidated to date in solution at room temperature. So far, low-energy electrons (LEEs; 0-20 eV) under vacuum condition and solvated electrons (esol-) in solution are shown to produce the σ-type C5-centered pyrimidine base radical through dissociative electron attachment involving carbon-halogen bond breakage. Formation of this σ-type radical and its subsequent reactions are proposed to cause cellular radiosensitization. Here, we report time-resolved measurements at room temperature, showing that a radiation-produced quasi-free electron (eqf-) in solution promptly breaks the C5-halogen bond in halopyrimidines forming the σ-type C5 radical via an excited transient anion radical. These results demonstrate the importance of ultrafast reactions of eqf-, which are extremely important in chemistry, physics, and biology, including tumor radiochemotherapy.

Metals, the plasma of the poor man?

The electron screening effect in the d(d,p)t reaction has been studied for deuterated metals, insulators, and semiconductors, i.e. 58 samples in total. As compared to measurements performed with a gaseous D2 target, a large effect has been observed in most metals, while a small (gaseous) effect is found e.g. for the insulators, semiconductors, and lanthanides. The periodic table provides the ordering of the observed small and large effects in the samples. An explanation of the large effects in metals is possibly provided by the classical plasma screening of Debye applied to the quasi-free metallic electrons. The data also provide information on the solubility of hydrogen in the samples.