Electron Quantum Research Articles

Bonding properties and crystal packing in β-(SeCl4)4 derived from Hirshfeld Atom Refinement.

Binary chalcogen halogen EX4 species represent intriguing systems in terms of chemical bonding theories, such as hypervalency and stereoactivity of lone electron pairs. Instead of a simple molecular EX4 structure, selenium tetrachloride forms an ionic pair, Cl3Se+Cl-, that assembles into a tetrameric (SeCl4)4 structure, namely, tetra-μ3-chlorido-dodecachloridotetraselenium. This article describes the charge-density analysis of the tetrameric molecule of β-SeCl4 based on the aspherical model obtained from Hirshfeld Atom Refinement of the tetrameric molecule and of an explicit cluster of 15 tetramers that simulates the crystal packing. Deformation density, electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) were used to evaluate the bonding situation, the electron-density distribution around the Se atom and the interaction energy of the tetramer.

Transport effects of twist-angle disorder in mesoscopic twisted bilayer graphene.

Magic-angle twisted bilayer graphene is a tunable material with remarkably flat energy bands near the Fermi level, leading to fascinating transport properties and correlated states at low temperatures. However, grown pristine samples of this material tend to break up into landscapes of twist-angle domains, strongly influencing the physical properties of each individual sample. This poses a significant problem to the interpretation and comparison between measurements obtained from different samples. In this work, we study numerically the effects of twist-angle disorder on quantum electron transport in mesoscopic samples of magic-angle twisted bilayer graphene. We find a significant property of twist-angle disorder that distinguishes it from onsite-energy disorder: it leads to an asymmetric broadening of the energy-resolved conductance. The magnitude of the twist-angle variation has a strong effect on conductance, while the number of twist-angle domains is of much lesser significance. We further establish a relationship between the asymmetric broadening and the asymmetric density of states of twisted bilayer graphene at angles smaller than the first magic angle. Our results show that the qualitative differences between the types of disorder in the energy-resolved conductance of twisted bilayer graphene samples can be used to characterize them at temperatures above the critical temperatures of the correlated phases, enabling systematic experimental studies of the effects of the different types of disorders also on the other properties such as the competition of the different types of correlated states appearing at lower temperatures.

Spontaneous photon emission by shaped quantum electron wavepackets and the QED origin of bunched electron beam superradiance.

It has been shown that the spontaneous emission rate of photons by free electrons, unlike stimulated emission, is independent of the shape or modulation of the quantum electron wavefunction (QEW). Nevertheless, here we show that the quantum state of the emitted photons is non-classical and does depend on the QEW shape. This non-classicality originates from the shape dependent off-diagonal terms of the photon density matrix. This is manifested in the Wigner distribution function and would be observable experimentally through homodyne detection techniques as a squeezing effect. Considering a scheme of electrons interaction with a single microcavity mode, we present a QED formulation of spontaneous emission by multiple modulated QEWs through a build-up process. Our findings indicate that in the case of a density modulated QEWs beam, the phase of the off-diagonal terms of the photon state emitted by the modulated QEWs is the harbinger of bunched beam superradiance, where the spontaneous emission is proportional to N_e^2 . This observation offers a potential for enhancement of other quantum electron interactions with quantum systems by a modulated QEWs beam carrying coherence and quantum properties of the modulation.

Polymorphism in Type-II Dirac Semimetal WSi2 under Pressure: Structural, Mechanical, and Electronic Insights.

The type-II Dirac candidate semimetal WSi2 is a promising candidate for electronic devices, quantum computing, and topological materials research, owing its distinct electronic structure and superior mechanical properties. Here, we synthesized high-quality WSi2 materials and systematically investigated their compressive behavior, and structural and electronic properties under high pressure using in-situ high pressure experiments, complemented by first-principles calculations. The results confirms that WSi2 has the properties of a type-II Dirac semimetal. Our results demonstrate that WSi2 maintains structural stability under high pressure but undergoes an electronic phase transition from a semimetal to a metal around 40 GPa. Additionally, the mechanical hardness softens discontinuously at this pressure. The structural stability of WSi2 under high pressure is attributed to the strong hybridization of Si-3p and W-5d electrons, the rigid crystal lattice, and the adaptable electronic structure. The pressure-induced electronic phase transition and softening are primarily governed by the energy band reconstruction and W-5d orbitals. This study provides valuable insights into the high-pressure behavior of type-II Dirac semimetal, highlighting their potential for advanced applications in electronic devices and topological quantum computing under extreme conditions by elucidating their structural stability and electronic phase transition mechanisms.

Electron transport and quantum phase transitions in cumulene-connected C80H20 fulleryne: DFT and tight-binding studies

Molecular bridges are opening up exciting new applications in diverse fields, improving the efficiency of conductive inks, enhancing the performance of devices such as organic light-emitting diodes and low-cost solar cells, and advancing the development of highly sensitive sensors, chemical reactions, drug delivery systems, and more. In this paper, we study the electron transport properties of a C80H20 fulleryne (dodecahedryne) connected to two cumulene electrodes. Using density functional theory (DFT), we determine the optimal molecular bridge structure. Based on the IR vibration spectra, different stable phases of the molecular bridge are obtained. The corresponding tight-binding (TB) parameters of the cage are obtained by assigning appropriate values of the length and type of bonds for the fulleryne cage through matching the HOMO-LUMO gap between the DFT calculations and the TB parameters. The electron transport for the desired structures is investigated using the obtained tight-binding parameters and the non-equilibrium Green's function (NEGF) method. Finally, it is concluded that among the five possible configurations for the cumulene-dodecahedryne -cumulene molecular bridge, only one specific configuration—where the electrodes are one edge apart—exhibits metallic behavior, while other positions act as insulators. In addition, the system exhibits quantum phase transitions from metal to semiconductor and from insulator to metal in the presence of critical electric fields. The ability to control quantum phase transitions in these molecular systems can be leveraged to develop qubits for quantum computing. The unique properties can be utilized to design advanced molecular electronic devices.

Quantum Carry Research of Q1D – SE on Helium at Charged Substrate

Known in nano-electronic a solid state quantum - size systems motivate they creating using the surface electrons over helium. The quantum carry of quasi-one-dimensional surface electrons (Q1D-SEs) over superfluid helium is considered here. Research performed according to an electron phase diagram in gas phase at conditions far from electron quantum melting. A substrate is dense row of the light-guide segments where the SEs channels are formed over helium in the fiber gaps. The electrostatic model of substrate profile demonstrates modulation of potential in the electric field leading to possibility of the fibers tops charge thereby improving the Q1D-SEs channels quality. The experiments carried out by a low - frequency electron transport method at the temperature from 1.5 K to 0.5 K and the concentrations of electrons were up to 109cm-2. The SE move transverse to channel satisfies conditions of quantization in sense both the temperature and the relaxation time of electron in a system. According to an experiment lower some temperature the SE conductivity is ladder-like. The differential of SE conductivity is peak-like corresponding qualitatively to an electron states density. The distance between peaks accords to the 1D energy spectrums in some approach. Possibility of apply the 1D-SEs quantized energy levels (vibration levels) as quantum bits of quantum computer is considered.

Molecular structure of 3-cyano-4-azido-1,2,5-oxadiazole 2-oxide studied by means of gas electron diffraction and quantum chemical calculations

Molecular structure of 3-cyano-4-azido-1,2,5-oxadiazole 2-oxide studied by means of gas electron diffraction and quantum chemical calculations

Unveiling sulfur vacancy pairs as bright and stable color centers in monolayer WS2

Color centers, arising from zero-dimensional defects, exploit quantum confinement to access internal electron quantum degrees of freedom, holding potential for quantum technologies. Despite intensive research, the structural origin of many color centers remains elusive. In this study, we employ in-situ cathodoluminescence scanning transmission electron microscopy combined with integrated differential phase contrast imaging to examine how defect configuration in tungsten sulfide determines color-center emission. Using an 80-kV accelerated electron beam, defects were deliberately produced, visualized, excited in situ and characterized in real time in monolayer WS2 within hBN|WS2 | hBN heterostructures at 100 K. These color centers were simultaneously measured by cathodoluminescence microscopy and differentiated by machine learning. Supported by DFT calculations, our results identified a crucial sulfur vacancy configuration organized into featured vacancy pairs, generating stable and bright luminescence at 660 nm. These findings elucidate the atomic-level structure-exciton relationship of color centers, advancing our understanding and quantum applications of defects in 2D materials.

Quantum efficiency enhancement of reflective GaAs photocathodes with exponential-doping structure generating a favorable built-in electric field

The rapid development of GaAs photocathodes has led to an increased focus on the attainment of high quantum efficiency. Three types of exponential-doping structures with a high to low doping concentration distribution from the interior to the surface are proposed for reflective GaAs emission layers. These three structures generate different built-in electric fields that facilitate photoelectron emission. The one-dimensional continuity equations for the increasing, constant, and decreasing types of built-in electric fields are derived, respectively. The electron concentration distribution and quantum efficiency varying with the wavelength are solved numerically by the finite difference method. The simulation results indicate that the quantum efficiency of the GaAs photocathode with the increasing type of built-in electric field is superior to that with the constant built-in electric field, while the GaAs photocathode with the decreasing type of built-in electric field shows the worst performance. Then, the designed GaAs photocathodes with the increasing and constant types of built-in electric fields are grown by metal-organic chemical vapor deposition and activated by cesium-oxygen alternating deposition. The measured spectral response curves show that the quantum efficiency of the GaAs photocathode with the increasing type of built-in electric field is higher in the whole band than that with the constant type of built-in electric field. In addition, the exponential-doping structure generating the increasing type of built-in electric field is beneficial for improving the surface potential barrier and increasing the surface electron escape probability.

A comprehensive Investigation of Donor-Acceptor anthraquinone derivatives as Versatile and efficient photosensitizers for Dye-Sensitized solar cells

A new metal-free anthraquinone donor–acceptor-π-anchor (D-A-π-A) design was developed using unsymmetrically substituted anthraquinone (ATQ) derivatives functionalized with bromine (Br), diphenylamine (DPA), indoline (Ind), BrATQBzOH, DPAATQBzOH, and IndATQBzOH. The synthesised compounds, functionalized with an anchor group (ethynylbenzoic acid), were evaluated in practical dye-sensitised solar cell, DSSC, devices with the aiming to improve electron injection efficiency. Their properties and applicability were analysed and rationalised based on their energy levels and parameters derived from the current–voltage (I-V) curve analysis in real devices. Femtosecond transient absorption measurements of the sensitiser IndATQBzOH with TiO2 revealed distinct excited state dynamics and charge transfer properties, highlighting the influence of the semiconductor interface. In addition, Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) electronic quantum calculations were performed, which revealed that the new anthraquinone-based dyes exhibit optimal coplanarity for efficient electron transfer, with their LUMO and HOMO energy levels facilitating electron injection into TiO2. In contrast to the low efficiencies found for previous anthraquinone derivatives, with maximum photocurrent efficiencies (PCE) below 0.2%, 9,10-anthraquinone derivatives were used as acceptors attached to suitable donors (DPA or Ind), and PCE above 1% were obtained.

Superconductivity in twisted bilayer WSe2.

Moiré materials have enabled the realization of flat electron bands and quantum phases that are driven by the strong correlations associated with flat bands1-4. Superconductivity has been observed, but only in graphene moiré materials5-9. The absence of robust superconductivity in moiré materials beyond graphene, such as semiconductor moiré materials4, has remained a mystery and challenged our current understanding of superconductivity in flat bands. Here we report the observation of robust superconductivity in both 3.5° and 3.65° twisted bilayer tungsten diselenide (WSe2), which hosts a hexagonal moiré lattice10,11. Superconductivity emerges near half-band filling and zero external displacement fields. The optimal superconducting transition temperature is about 200 mK in both cases and constitutes about 1-2% of the effective Fermi temperature; the latter is comparable to the value in high-temperature cuprate superconductors12 and suggests strong pairing. The superconductor borders on two distinct metals below and above half-band filling; it undergoes a continuous transition to a correlated insulator by tuning the external displacement field. The observed superconductivity on the verge of Coulomb-induced charge localization suggests roots in strong electron correlations12,13.

Dissecting the hydrogen bond network of water: Charge transfer and nuclear quantum effects

The molecular structure of water is dynamic, with intermolecular (H)-bond interactions being modified by both electronic charge transfer and nuclear quantum effects (NQEs). Electronic charge transfer and NQEs potentially change under acidic / basic conditions, but such details have not been measured. Here, we developed correlated vibrational spectroscopy, a symmetry-based method that distinctively separates interacting from non-interacting molecules in self- and cross-correlation spectra, giving access to previously inaccessible information. We found that OH − donated ~8% more negative charge to the H-bond network of water and H 3 O + accepted ~4% less negative charge from the H-bond network of water. D 2 O had ~9% more H-bonds compared to H 2 O, and acidic solutions displayed more dominant NQEs than basic ones.

Conformations of α-cyclodextrin and its role on the stability of inclusion complexes in aqueous solution

α-Cyclodextrin (αCD), a cyclic carbohydrate polymer, presents a wealth of opportunities for drug delivery and various industrial applications. Its high affinity and selectivity in encapsulating target molecules have been well-documented. However, the influence of αCD's conformational variations on its encapsulation capacity remains a promising area for further exploration. This study explores the conformational dynamics of αCD and its relationship with the formation of inclusion complexes (ICs) in aqueous solutions, focusing on understanding the forces driving these dynamics and the formation of stable ICs. Classical molecular dynamics (CMD) demonstrate that αCD solvated in water can adopt two conformations: a truncated cone shape with a suitable cavity for encapsulation and a distorted cone shape with a collapsed cavity. The predominant conformation observed in the CMD trajectory of pristine αCD is the distorted cone. However, under complexation conditions with aliphatic molecules, the guest molecule's size dictates the ICs' stability, forcing αCD to maintain the truncated cone conformation. Quantum chemistry methods and electron density analyses (Quantum Theory of Atoms in Molecules and Non-Covalent Interactions index) support CMD observations by characterizing and quantifying non-covalent interactions. Findings indicate that the shift from the truncated to the distorted cone conformation in αCD is primarily driven by intramolecular non-covalent interactions and the reconfiguration of water molecules surrounding αCD. The ICs' analysis displays a significant correlation between the size of the aliphatic chain and the intensity of intermolecular interactions. The strength of these interactions can effectively disrupt the αCD intramolecular non-covalent interactions that lead to a conformational change and, consequently, the loss of the inclusion complex. In conclusion, although αCD's conformational change can affect encapsulation, guest molecules can manipulate the conformational preference. The systematic analysis of non-covalent interactions offers a way to characterize and quantify these forces, enhancing our ability to understand and predict the stability of inclusion complexes.

Tailoring Single-Electron Emission Distributions in the Time-Energy Phase Space.

The precise characterization and control of single-electron wave functions emitted from a single-electron source are essential for advancing electron quantum optics. Here, we introduce a method for tailoring a single-electron emission distribution using energy filtering, enabling selective control of the distribution under various energy barrier conditions of the filter. The tailored electron is studied by reconstructing its Wigner distribution in the time-energy phase space using the continuous-variable tomography method. Our results reveal that the filtering cuts the portion of the distribution below the energy-barrier height of the filter in the time-energy space. While the filtering is demonstrated in a classical regime of the emitted electrons, we expect that this study significantly contributes to the design and implementation of advanced experiments toward quantum information processing based on single electrons.

Different built-in electric fields for transmission-mode GaAs photocathodes through doping engineering: Design and modeling

In order to enhance the emission performance of transmission-mode GaAs photocathodes used in optoelectronic field, different exponential doping structures are designed for the GaAs emission layer to generate different types of built-in electric fields. These built-in electric fields include the constant, increasing and decreasing types, which can help photoelectron transport toward the emission surface. By solving the one-dimensional continuity equation using the finite difference method, the electron concentration distribution and quantum efficiency of the three types of exponential doping GaAs photocathodes are derived. Meanwhile, the light absorption distributions in the emission layer are simulated by the finite difference time domain method. By comparing the optical absorption distribution and the electron concentration distribution, it is concluded that, among the three types of exponential doping structures, the exponential doping structure generating the increasing built-in electric field has the most sufficient long-wave light absorption capacity and the strongest photoelectron transport ability, thereby achieving the highest quantum efficiency. This theoretical work can help understand the mechanism of improving the photoemission performance of GaAs photocathodes through doping engineering.

Computational analysis of 1T-MoS2: Probing the interplay of layer-dependent electronic structure, quantum capacitance, charge density and mechanical properties

To meet the high energy demand of society, a conversion to renewable energy sources has become essential and energy should be appropriately stored for future use. This has led to the development of energy-storing devices such as supercapacitors (SCs). To enhance capacitive behavior, the concept of quantum capacitance (CQ) is unveiled, which results from the confinement of electrons in their energy states. In this work, 1T phase of MoS2 is studied as it has received a lot of attention because of its wide applications in the energy storage devices and electronics. Here, the electronic structure, CQ and surface charge density (σ) of one, two and three-layered structures of 1T phase is studied using Density Functional Theory. No bandgap is obtained in the Density of States (DOS) and the bands plot of 1T structure indicates their metallic character and the DOS is continuous in all three layers. The CQ of three-layered structure dominates over the other two layers throughout the potential window. The larger CQ and σ values are obtained as 1718.06 μF cm−2 and -1299.50 μC cm−2 for three-layered structure at −0.27 V and −1 V respectively. For analyzing the mechanical strength, Young's modulus is evaluated for optimized structure by applying uni-axial strain. The value is obtained as 177.37 GPa, which is a measure of elastic deformation behavior. The results suggest that the capacitive performance of 1T MoS2 for SC applications is better and it can function as flexible cathode material for asymmetric SC applications.

Temperature dependence of the electron quantum lifetime in InGaAs/GaAs double quantum well: Fukuyama-Abrahams mechanism

In the n-InGaAs/GaAs double quantum well, the suppression of resonant resistance by an in-plane magnetic field B ≤ 9 T in the temperature range T = (1.8–70) K is studied. The electron quantum lifetime, τq, is determined and the contributions of various scattering mechanisms to τq(T) are separated. It is shown that the observed nonmonotonic temperature dependence of the electron quantum lifetime is due to a combination of the interference contribution from the exchange electron-electron interaction in the ballistic regime and the inelastic electron-electron scattering in the diffusion regime (Fukuyama-Abrahams mechanism).

A Theoretical Approach to the Investigation of Electrostatic Plasma Waves in Laser Pulse Interaction with Hypothetical Nonuniform Quantum Electron–Positron Magnetoplasma

A Theoretical Approach to the Investigation of Electrostatic Plasma Waves in Laser Pulse Interaction with Hypothetical Nonuniform Quantum Electron–Positron Magnetoplasma

Observation of Circular Dichroism Induced by Electronic Chirality.

Chiral phases of matter, characterized by a definite handedness, abound in nature, ranging from the crystal structure of quartz to spiraling spin states in helical magnets. In 1T-TiSe_{2} a source of chirality has been proposed that stands apart from these classical examples as it arises from combined electronic charge and quantum orbital fluctuations. This may allow its chirality to be accessed and manipulated without imposing either structural or magnetic handedness. However, direct bulk evidence that broken inversion symmetry and chirality are intrinsic to TiSe_{2} remains elusive. Here, employing resonant elastic x-ray scattering technique, we reveal the presence of circular dichroism, i.e., polarization dependence of the resonant diffraction intensity, up to ∼40% at forbidden Bragg peaks that emerge at the charge and orbital ordering transition. The dichroism varies dramatically with incident energy and azimuthal angle. Comparison to calculated scattering intensities traces its origin to bulk chiral electronic order in TiSe_{2} and establishes resonant elastic x-ray scattering as a sensitive probe to electronic chirality.

Screening nitrogen-fixing cyanobacteria that can alleviate cadmium toxicity to rice and reduce cadmium accumulation in brown rice

Among food crops, rice is the most serious food crop contaminated with cadmium (Cd). It is critical to reduce Cd bioavailability in the soil and prevent its accumulation in brown rice. The use of microorganisms to lessen Cd toxicity in rice has been the subject of numerous studies carried out in recent years. The nitrogen-fixing cyanobacterium (NFC) is a potent biofertilizer and heavy metal biosorbent. However, there is a dearth of research on the impact of NFC supplementation on rice's susceptibility to Cd poisoning. This study screened for Cd-tolerant NFCs and assessed how well they might promote growth and lower the amount of Cd in rice. Four NFCs with tolerance to 1 mg L−1 Cd were selected from ten NFCs. The results of seedling experiment showed that SCAU-10 treatment increased plant height and biomass while reducing Cd levels in seedlings by 62.0 %. The pot experiment also demonstrated that SCAU-10 was effective in lowering Cd content in brown rice by 85.3 %. Reducing the bioavailability of soil Cd, shielding rice roots, preventing Cd transfer from below to above ground, generating phytohormones, and enhancing the photochemical electron quantum yield of rice leaves are a few possible action mechanisms of the NFC. It indicates that Trichormus sp. SCAU-10 has a great deal of promise for use as a biofertilizer in the safe management of Cd-contaminated rice fields. This is the first report on using Trichormus sp. biofertilizer for relieving the toxicity of Cd to rice and reducing Cd accumulation in brown rice.