Dielectric Quantum Research Articles

Impurity affected transport properties of quantum well heterostructures with electronic and high-κ dielectric quantum screening

The effect of electronic and high-κ dielectric quantum screening (ES and DS) on the impurity-limited electron transport properties of quantum well/high-κ dielectric barrier type heterostructures with two-dimensional electron gas (2DEG) is studied theoretically. Characteristic of these heterosystems the 2D compound forms of screened impurity potential are employed for the first time. In the framework of 2D Debye-Hückel potential form an electron momentum relaxation time (τ) expression depending on the impurity 2D screening radius is obtained analytically. A numerical analysis of τ is carried out for the realistic HfO/InSb/HfO2QW heterostructure taking account both the finite mismatch of the energy bands at the heterointerface and the energy band non-parabolicity of InSb. The contributions of screened potential compound 2D forms to τ are established depending on QW width. A significant suppression of the scattering rate τ−1 (by an order of magnitude) is received with accounting of ES + DS combined effect.

Revisiting Dynamic Processes and Relaxation Mechanisms in a Heterocyclic Glass-Former: Direct Observation of a Transient State.

Despite decades of studies, a clear understanding of near-Tg phenomena remains challenging for glass-forming systems. This review delves into the intricate molecular dynamics of the small, heterocyclic thioether, 6-methyl-2,3-dihydro-1,4-benzodithiine (MeBzS2), with a particular focus on its near-Tg cold crystallization and relaxation mechanisms. Investigating isothermal crystallization kinetics at various temperatures reveals a significant interplay between its molecular dynamics and recrystallization from a supercooled liquid. We also identify two independent interconversion paths between energetically privileged conformers, characterized by strained transition states. We demonstrate that these spatial transformations induce substantial alterations in the dipole moment orientation and magnitude. Our investigation also extends to the complex salt PdCl2(MeBzS2), where we observe the transient conformers directly, revealing a direct relationship between their abundance and the local or macroscopic electric field. The initially energetically privileged isomers in an undisturbed system become less favored in the presence of an external electric field or ions, resulting even in an unexpected inversion of states. Consequently, we confirm the intramolecular character of secondary relaxation in MeBzS2 and its mechanism related to conformational changes within the heterocyclic ring. The research is based on the combination of broadband dielectric spectroscopy, X-ray diffraction, and quantum density functional theory calculations.

Experimental characterization of Spherical Bragg Resonators for electromagnetic emission engineering at microwave frequencies

This work reports experimental investigation and numerical validation of millimeter-sized Spherical Bragg Resonators (SBRs) fabricated using 3D printing technology. The frequency dependencies of the reflection and transmission coefficients were analyzed, and eigenfrequency values were calculated to examine the density of photonic states in air/PLA-polylactide SBRs, showing the appearance of an eigenmode and an increase in the local density of states in the core of a defect cavity. A decay rate enhancement of {sim 10}^{2} was obtained for a dipole placed in the core of the defect SBR. The study also investigated the influence of the source position on the resonator's electromagnetic wave energy. Scattering efficiencies up to order twelve of the multipole electric and magnetic contribution in a 10-layer SBR were calculated to validate the presence of the resonant modes observed in the scattering measurements performed for parallel and perpendicular polarizations. The results demonstrate that SBRs can act as omnidirectional cavities to enhance or inhibit spontaneous emission processes by modifying the density of electromagnetic states compared to free space. This finding highlights the potential of SBRs engineering spontaneous electromagnetic emission processes in various applications, including dielectric nanoantennas, optoelectronics devices, and quantum information across the entire electromagnetic spectrum.

Lanthanum doped hybrid LaxBi2−xSn2O7/SnO2(β-Bi2O3) nanostructures for energy storage applications

Hybrid-phase metal oxides are known for immense and insistent daily life applications which makes them capable and competent for tremendous number of applications such as electrode material design, energy storage devices and fuel cells. In this context, a series of LaxBi2−xSn2O7/SnO2(β-Bi2O3) nanostructures is reported, synthesized preferably by using sol-gel technique. Lanthanum was replaced with bismuth with a doping concentration of (x = 0.0–1.0) with 0.2 step size and it was finely tuned within the lattice. Presence of hybrid phase metal oxides was confirmed after XRD analysis which was consistent with TEM results. These hybrid-phase metal oxides form heterojunction, working with multifunctional pyrochlore, which increases the dielectric constant and quantum efficiency of material. Electrical parameters like AC conductivity, impedance, dielectric constant, electric modulus and tangent loss were also studied via impedance analyzer meter at high frequencies (1 MHz–3 GHz). A detailed study of relaxation mechanisms was discussed showing the different polarization stages in applied frequency range. The appearance of relaxation peaks at different frequency exhibit high dielectric constant can make a prepared hybrid nanocomposites is suitable for energy storage devices for a wide range of frequency.

Non-covalent interactions involving π effect between organic cations in low-dimensional organic/inorganic hybrid perovskites

Low-dimensional organic/inorganic hybrid perovskites (OIHPs) are a promising class of materials with a wide range of potential applications in optoelectronics and other fields since these materials can synergistically combine individual features of organic molecules and inorganics into unique properties. Non-covalent interactions are commonly observed in OIHPs, in particular, π-effect interactions between the organic cations. Such non-covalent interactions can significantly influence important properties of the low-dimensional OIHPs, including dielectric confinement, bandgap, photoluminescence, quantum efficiency, charge mobility, trap density, stability, and chirality. This perspective reviews recent studies of non-covalent interactions involving the π systems of organic cations in low-dimensional OIHPs. The analysis of crystal structures of low-dimensional OIHPs offers significant insight into understanding such non-covalent interactions and their impacts on specific properties of these OIHPs. The developed structure–property relationships can be used to engineer non-covalent interactions in low-dimensional OIHPs for applications.

Magnetic light amplification by stimulated emission of radiation in subwavelength systems of a dielectric cavity and magnetic quantum emitters

We propose a magnetic laser in a subwavelength system consisting of a high-refractive-index dielectric cavity and an active medium formed by magnetic quantum emitters. Stimulated emissions of magnetic quantum emitters induced by their coherent interactions with quantized magnetic fields of a cavity are theoretically considered. The condition to achieve such a magnetic laser is obtained. Numerical results show that magnetic lasers are feasible in some realistic systems, for example, a silicon disk of high-quality whispering gallery modes with embedded emitters. Furthermore, the competitions between the electric interaction and magnetic one in terms of their Purcell factors are also considered in some magnetic laser achievable systems. In a wavelength-scale silicon block of a high-order magnetic mode, the ratio of magnetic Purcell factor to the electric one can reach more than $\ensuremath{\sim}{10}^{3}$ large. Our results open up ways to enhanced magnetic light-matter interactions.

In English

In review, deals with the theory of exciton quasimolecules (formed of spatially separated electrons and holes) in a nanosystems that consists of semiconductor and dielectric colloidal quantum dots (QDs) synthesized in a dielectric and semiconductor matrixs. It has been shown that the exciton quasimolecule formation is of the threshold character and possible in a nanosystem, where the distance D between the surfaces of QD is given by the condition (where and are some critical distance). We have shown that in such a nanoheterostructures acting as “exciton molecules” are the QDs with excitons localizing over their surfaces. The position of the quasimolecule state energy band depends both on the mean radius of the QDs, and the distance between their surfaces, which enables one to purposefully control it by varying these parameters of the nanostructure. It was found that the binding energy of singlet ground state of exciton quasimolecules, consisting of two semiconductor and dielectric QDs is a significant large values, larger than the binding energy of the biexciton in a semiconductor and dielectric single crystals almost two orders of magnitude. It is shown that the major contribution to tue binding energy of singlet ground state of exciton quasimolecule is made by the energy of the exchange interaction of electrons with holes and this contribution is much more substantial than the contribution of the energy of the Coulomb interaction between the electrons and holes. It is established that the position of the exciton quasimolecule energy band depends both on the mean radius of the QDs and the distance between their surfaces. It is shown that with increase in temperature above the threshold (), a transition can occur from the exciton quasimolecule to exciton state. It has been found that at a constant concentration of excitons (i.e. constant concentration of QD) and temperatures Т below , one can expect a new luminescence band shifted from the exciton band by the value of the exciton quasimolecule binding energy. This new band disappears at higher temperatures (). At a constant temperature below , an increase in exciton concentration (i.e. in QD concentration) brings about weakening of the exciton luminescence band and strengthening of the exciton quasimolecule. These exciton quasimolecules are of fundamental interest as new quasi-atomic colloidal nanostructures; they may also have practical value as new nanomaterials for nanooptoelectronics. The fact that the energy of the ground state singlet exciton quasimolecule is in the infrared range of the spectrum, presumably, allow the use of a quasimolecule to create new infrared sensors in biomedical research.

Polyatomic time crystals of the brain neuron extracted microtubule are projected like a hologram meters away

When a perturbed periodic oscillation dephases, the system edits it to retrieve the original clock. The inherent clock born during retrieval is the time crystal. Time crystals have been explored for five decades, and only one inherent clock was detected in biological and artificial systems. Only one type of atom is used in those time crystals, but two or more atom types would lead to multi-functional and programmable time crystals. No such concept was ever conceived. Here, we demonstrate a multi-clock time crystal or a polyatomic time crystal in the brain neuron-extracted microtubule nanowire using dielectric resonance and quantum optics experiments. Earlier, one used to artificially reset the phase of an inherent clock to find a time crystal. Instead, we map how a biomaterial spontaneously generates distinct new clocks at many time domains at a time. We observe multiple time-symmetry-breaking events at a time. Moreover, unlike conventional time crystal research, we searched for polyatomic time crystals at least 103 orders lower than the excitation frequency region. Conventional time crystals could be rejected, arguing that inherent clocks born after the breaking of time symmetry are harmonics of the external input, and such an argument will not hold for us. Moreover, quantum experiments revealed a method to synthesize and fuse distinct clocks in one hologram as a polyatomic time crystal and project it like an antenna meters away. The discovery of material-like holographic engineering of polyatomic time crystals would make them useful.

Quantum edge plasmon excitations and electron spill-out effect

In this paper, by using the effective Schrödinger–Poisson model, we investigate quantum edge plasmon excitations and electron spill-out effect in an arbitrary degenerate electron gas in the presence of perpendicular electron drift momentum. It is found that the single-electron Schrödinger equation solution produces a nonoscillatory electron number density distribution on the interface showing characteristic surface-dipole and electron spill-out effects. However, the Schrödinger–Poisson model produces large amplitude dual-tone density distribution due to both wave-like and particle-like plasmon dispersion other than surface-dipole and electron spill-out effects. The variations in the density structure are investigated in terms of different parameters such as the chemical potential, temperature, quantum electron tunneling parameter, and perpendicular electron de Broglie's wavenumber. Furthermore, we extend our study to the case of collective electron tunneling and reveal that the interface potential energy significantly differs from the case of single-electron quantum tunneling and strongly depends on the electron gas parameters. The current study reveals interesting features of the transverse plasmon excitations and electron spill-out in a current carrying narrow metal slab or metal–dielectric quantum sandwich interfaces incorporating both single-electron and collective quantum tunneling.

Simple Rules for Complex Near-Glass-Transition Phenomena in Medium-Sized Schiff Bases.

Glass-forming ability is one of the most desired properties of organic compounds dedicated to optoelectronic applications. Therefore, finding general structure–property relationships and other rules governing vitrification and related near-glass-transition phenomena is a burning issue for numerous compound families, such as Schiff bases. Hence, we employ differential scanning calorimetry, broadband dielectric spectroscopy, X-ray diffraction and quantum density functional theory calculations to investigate near-glass-transition phenomena, as well as ambient- and high-pressure molecular dynamics for two structurally related Schiff bases belonging to the family of glycine imino esters. Firstly, the surprising great stability of the supercooled liquid phase is shown for these compounds, also under high-pressure conditions. Secondly, atypical self-organization via bifurcated hydrogen bonds into lasting centrosymmetric dimers is proven. Finally, by comparing the obtained results with the previous report, some general rules that govern ambient- and high-pressure molecular dynamics and near-glass transition phenomena are derived for the family of glycine imino esters. Particularly, we derive a mathematical formula to predict and tune their glass transition temperature (Tg) and its pressure coefficient (dTg/dp). We also show that, surprisingly, despite the presence of intra- and intermolecular hydrogen bonds, van der Waals and dipole–dipole interactions are the main forces governing molecular dynamics and dielectric properties of glycine imino esters.

A Compact Model of Gate Capacitance in Ballistic Gate-All-Around Carbon Nanotube Field Effect Transistors

This paper presents a one-dimensional analytical model for calculating gate capacitance in Gate-All-Around Carbon Nanotube Field Effect Transistor (GAA-CNFET) using electrostatic approach. The proposed model is inspired by the fact that quantum capacitance appears for the Carbon Nanotube (CNT) which has a low density of states. The gate capacitance is a series combination of dielectric capacitance and quantum capacitance. The model so obtained depends on the density of states (DOS), surface potential of CNT, gate voltage and diameter of CNT. The quantum capacitance obtained using developed analytical model is 2.84 pF/cm for (19, 0) CNT, which is very close to the reported value 2.54 pF/cm. While, the gate capacitance comes out to be 24.3×10-2 pF/cm. Further, the effects of dielectric thickness and diameter of CNT on the gate capacitance are also analysed. It was found that as we reduce the thickness of dielectric layer, the gate capacitance increases very marginally which provides better gate control upon the channel. The close match between the calculated and simulated results confirms the validity of the proposed model.

Impact of Sn4+ substitution in Mg–Zn ferrites: Deciphering the structural, morphological, dielectric, electrical and magnetic properties

From the viewpoint of enormous applications and research, ferrite materials have already been achieved the status of one of the important branches of materials science. In this report, we have tuned the physical properties of Mg–Zn ferrites by Sn substitution investigated using X-ray diffraction, field emission scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, electrical and dielectric properties and quantum design physical properties measurement system. The Mg0·5Zn0.5SnxFe2-xO4 (0 ≤ x ≤ 0.10) samples have been synthesized by the conventional ceramic technique. The studied ferrites exhibits the single-phase up to x = 0.08 where an increase in lattice constant was observed. The FESEM images revealed the microstructure and the energy dispersive spectroscopy (EDS) confirms the absence of any unwanted elements. The increase (decrease) in bulk density (porosity) was associated with the variation of average grain size. FTIR spectra confirmed the formation of spinel structure. The dielectric polarization or conduction mechanism in these materials is due to the hopping of charge carriers at the octahedral sites. The common dielectric behavior of studied compositions is also observed. The substitution of Sn ions leads to enhanced dielectric constant and ac conductivity due to increased hopping of charge carriers. Complex impedance spectroscopy study revealed the non-Debye type of relaxation process within the studied compositions with a dominant contribution from grain boundary resistance. The dynamic magnetic hysteresis loops are measured to obtain the magnetic parameters. The low values of coercivity revealed the soft magnetic nature of the studied compositions. The obtained saturation magnetization (Ms) for Mg–Zn ferrite (x = 0.00) is comparable with the prior result. Non-linear decrease of Ms (62-44 emu/g) due to Sn substitution is explained based on the variation of magnetic moments over A- and B-sites. The squareness ratio (Mr/Ms) revealed that the magneto-statical interaction is present within the synthesized samples. The constant value of initial permeability (μʹ) over a wide range of frequencies revealed the compositional stability and quality of the prepared ferrite. The variation of μʹ with Sn content is similar to that of Msvs Sn contents. Moreover, theoretical cation distribution and the effect of Sn substitution on the related parameters have also been studied. The studied parameters are compared with the reported results, where available.

Optical absorption by a nanosystem with dielectric quantum dots

The mechanisms of formation of the spectra of interband optical absorption in nanosystems containing aluminum oxide quantum dots, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the band of the electron–hole pair states cause absorption in the ultraviolet wavelengths and cause the experimentally observed significant blurring of the absorption band.

Optical absorption by electron states in nanosystem containing dielectric quantum dots

In the framework of dipole approximation, it is shown that the oscillator strengths of transitions as well as the dipole moments for transitions for one-particle electron quantum-confined states emerging above the spherical surface quantum dot of aluminum oxide assume giant values considerably (by two orders of magnitude) exceeding the typical values of the corresponding quantities for dielectrics. It has been established that the giant values of the light absorption cross section in the nanosystems under investigation make it possible to use such nanosystems as strongly absorbing nanomaterials in a wide range of infrared waves with a wavelength that can be varied in a wide range depending in the type of contacting materials.

Nonlinear optical properties of semiconductor double quantum wires coupled to a quantum-sized metal nanoparticle

We theoretically investigate linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs) of two quantum wires (QWs) separated by a quantum-sized metal nanoparticle (MNP) using a density matrix method and dielectric quantum theory. The exciton-plasmon coupling and the dipole-dipole interaction (DDI) between the two QWs are taken into account. We find that the magnitudes of the linear and nonlinear OACs (RICs) from the QWs are enhanced by one order of magnitude, in contrast to the case without a MNP, due to the exciton-plasmon coupling and the DDI between the two QWs. The quantum size effect in a MNP induces a pronounced enhancement in the magnitudes of the linear and nonlinear OACs (RICs) with the increase of the MNP radius. Furthermore, the optical responses can be further strengthened via increasing the MNP radius or decreasing the radius and gap of the QWs, owing to the enhanced exciton-plasmon coupling and the DDI between the two QWs. Moreover, the magnitudes of the total OACs (RICs) are reduced by increasing the optical intensity, along with a splitting effect of the OACs under strong optical intensity. Our results provide the possibility of designing the hybrid nanostructures with large nonlinearity for applications in nano-devices such as optical switches and amplifiers.

Coherent couplings between magnetic dipole transitions of quantum emitters and dielectric nanostructures

Here we study theoretically the optical responses of hybrid structures composed of dielectric nanostructures and quantum emitters with magnetic dipole transitions. Coherent couplings between magnetic dipole transitions and magnetic modes can occur, leading to giant modifications of the extinction spectra of the constituents in the hybrid structures. For a given hybrid structure, the extinction-cross-section spectra show linear or nonlinear behaviors depending on the strength of the excitation field. For a weak excitation, the extinction of the quantum emitters is greatly enhanced. The hybrid structure shows a dip on its extinction spectrum. For a strong excitation, the resonant extinction of the quantum emitters is weakly enhanced while the extinction spectrum is broadened obviously. The hybrid structure shows a Fano-like line shape on its extinction spectrum, which is different from that with a weak excitation. This difference is highly related to the behaviors of the magnetic polarizabilities of the quantum emitters in the hybrid structure. The optical responses of hybrid structures can be largely tuned by varying the geometric and material parameters.

In-situ fabricated anisotropic halide perovskite nanocrystals in polyvinylalcohol nanofibers: Shape tuning and polarized emission

We report an in-situ fabrication of halide perovskite (CH3NH3PbX3, CH3NH3 = methylammonium, MA, X= Cl, Br, I) nanocrystals in polyvinylalcohol (PVA) nanofibers (MAPbX3@PVA nanofibers) through electrospinning a perovskite precursor solution. With the content of the precursors increased, the resulting MAPbBr3 nanocrystals in PVA matrix changed the shape from ellipsoidal to pearl-like, and finely into rods-like. Optimized MAPbBr3@PVA nanofibers show strong polarized emission with the photoluminescence quantum yield of up to 72%. We reveal correlations between the shape of in-situ fabricated perovskite nanocrystals and the polarization degree of their emission by comparing experimental data from the single nanofiber measurements with theoretical calculations. Polarized emission of MAPbBr3@PVA nanofibers can be attributed to the dielectric confinement and quantum confinement effects. Moreover, nanofibers can be efficiently aligned by using parallel positioned conductor strips with an air gap as collector. A polarization ratio of 0.42 was achieved for the films of well-aligned MAPbBr3@PVA nanofibers with a macroscale size of 0.5 cm × 2 cm, which allows potential applications in displays, lasers, waveguides, etc.

A quantum dot model for nanoparticles in polymer nanocomposites

Nanoparticles in polymer nanocomposites can be dielectric quantum dots (DQDs). A quantum dot model is proposed for nanoparticles imbedded in polymers based on both this new concept and the multicore model proposed in 2005. QDs should be as small as de Broglie's wavelength and the exciton Bohr diameter, and accommodate a countable number of charge carriers. DQDs are a little bit larger than metal and semiconductor QDs. Some of dielectric performances such as permittivity, charge transport, space charge and treeing can be explained in terms of nonlinear multi-functional traps derived from the DQD model. It was verified that different combination of polymers and nanoparticles lead to different characteristics.

Optical spectroscopy of excitons with spatially separated electrons and holes in nanosystems containing dielectric quantum dots

It is shown that in the potential energy of an exciton of spatially separated electrons and holes [hole moves in the amount of quantum dots (QDs), the electron is localized on a spherical surface section (QD—dielectric matrix)], taking into account centrifugal, energy gives rise band of the quasistationary surface exciton states that with the increase of the radius of QD becomes stationary state. The mechanisms of formation of the spectra of interband and intraband absorption (emission) of light in nanosystems containing aluminum oxide QDs, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the area of the surface exciton states cause significant absorption in the visible and near-infrared wavelengths and cause the experimentally observed significant blurring of the absorption edge.

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Summary Inorganic CsPbX3 perovskites have gained great attention owing to their excellent thermal stability and carrier transport properties. However, the power conversion efficiency (PCE) of solution-processed CsPbX3 perovskite solar cells is still far inferior to that of their hybrid analogues. Insufficient film thickness and undesirable phase transition are the two major obstacles limiting their device performance. Here, we show that by adopting a new precursor pair, cesium acetate (CsAc) and hydrogen lead trihalide (HPbX3), we were able to overcome the notorious solubility limitation for Cs precursors to fabricate high-quality CsPbX3 perovskite films with large film thickness (∼500 nm). We further introduced a judicious amount of phenylethylammonium iodide (PEAI) into the system to induce reduced-dimensional perovskite formation. Unprecedentedly, the resulting quasi-2D perovskites significantly suppressed undesirable phase transition and thus reduced the film's trap density. Following this approach, we reported a state-of-the-art PCE to date, 12.4%, for reduced-dimensional α-CsPbI3 perovskite photovoltaics with greatly improved performance longevity.