Local Field Effects Research Articles

Nonlinear bosonization of Fermi surfaces: The method of coadjoint orbits

We develop a method for bosonizing the Fermi surface based on the formalism of the coadjoint orbits. This allows one to parametrize the Fermi surface by a bosonic field that depends on the spacetime coordinates and on the position on the Fermi surface. The Wess-Zumino-Witten term in the effective action, governing the adiabatic phase acquired when the Fermi surface changes its shape, is completely fixed. As an effective field theory the action also involves a Hamiltonian, which contains, beside the kinetic energy and the Landau interaction, terms with arbitrary number of derivatives and fields. We show that the resulting local effective field theory captures both linear and nonlinear effects in Landau's Fermi liquid theory. The approach can be extended to incorporate spin degrees of freedom and the charge-2 fields corresponding to the BCS order parameter.

Investigation of the Second Harmonic Generation at the Water-Vacuum Interface by Using Multi-Scale Modeling Methods.

The Sequential Quantum Mechanics/Molecular Mechanics scheme has been enacted to perform a systematic investigation of the polarizability (α) and first hyperpolarizability (β) responses at the water-vacuum interface. After performing classical molecular dynamics simulations to provide snapshots of the structures, quantum chemistry calculations of the linear and nonlinear optical responses have been performed for clusters of five water molecules at the time-dependent DFT level in combination with different embedding schemes, ranging from point charges to polarizable point charges, with and without local field effects. When going from the bulk to the interface, the main observations of these calculations encompass i) a modest increase of the average polarizability but an increase by about a factor of two of its anisotropy, ii) an increase by about 20 % of the βHRS response, accompanied by a small increase of its depolarization ratio, and iii) a net increase of the component of the β tensor normal to the interface (βzzz ) as well as of β// . Globally, the interfacial effects on β are localized at the first molecular layer while they are observed up to the fourth molecular layer on α.

New Gibbs measures of the Ising model on a Cayley tree in the presence of triple effective local external fields

In this paper, we consider the Ising model on a Cayley tree in the presence of competing binary and prolonged ternary interactions and triple effective local external fields (TELEFs). We investigate Gibbs measures with memory of length 2 for the given Ising model using a measure-theoretic approach. We examine whether the TELEFs change the number of Gibbs measures. We also determine under what conditions the phase transition occurs.

Structural and optical characterization of tungsten phosphate glasses containing silver and erbium

Tungsten-phosphate glasses with up to 20 mol% of silver chloride content were prepared using the conventional melt-quenching method. Ag nanoparticles (AgNPs) formation was achieved by nucleation and growth using controlled thermal treatment. Thermal properties and the local structure were studied as a function of Ag content by means of DSC, Raman and 31P MAS NMR spectroscopy. The Ag NP growth was monitored by real-time UV–Vis spectroscopy and confirmed by TEM. The optical linear and nonlinear properties were evaluated as a function of the AgNPs growth. NIR emission of Er3+ ions was studied and showed a strong dependence on the AgNPs size. A weak luminescent enhancement occurs when small AgNPs are present, but on the other hand, a strong quenching takes place in the presence of larger AgNPs, due to the local field effect mediated by surface plasmon resonance (SPR) and Er3+ intersystem crossing processes, respectively. A stronger luminescence suppression by excitation at 545 nm was assigned to the increased contribution to back-energy transfer from Er3+ to AgNPs and re-absorption by SPR. These results highlight the importance of a careful study of the relation between noble metal NPs size and the excitation wavelength to increase the efficiency of the future photonic devices, such as NIR solid state laser, Kerr effect-based laser or amplifiers.

Optical response of two-dimensional systems: Insights from classical electromagnetism to ab initio calculations

Quasi-two-dimensional objects appear to be promising for the development of new optical devices since their electronic properties are expected to be governed by their size. The understanding of these properties can be achieved by means of theoretical spectroscopy based on the state-of-the-art ab initio formalisms. Time-dependent density functional theory is well suited since it accounts for the local field effects, which are expected to be large at the interfaces with vacuum. This framework allows the calculation of the response function to the external potential. For bulk materials, this quantity is related to the macroscopic dielectric function following the Adler and Wiser formula. This expression contains dimensionless quantities, while for the two-dimensional object, the physical observables should be proportional to the thickness. In this paper, we propose a mixed-space approach which allows us to calculate in a direct way the out-of-plane component and to evidence how the ambiguity on the thickness of the slab affects the calculation of the macroscopic dielectric function. The classical Lorentz model adapted to a thin slab reveals how the huge change of the induced electric field, and the arising of a transverse polarization, lead to modify the expression of the macroscopic dielectric function to get the absorption spectrum. Despite the influence of the thickness of the slab on the macroscopic dielectric function, the optical response resulting from the classical electromagnetism can be unambiguously calculated from the mixed-space simulations.

Directional and inter-acquisition variability in diffusion-weighted imaging and editing for restricted diffusion.

PurposeTo evaluate and quantify inter‐directional and inter‐acquisition variation in diffusion‐weighted imaging (DWI) and emphasize signals that report restricted diffusion to enhance cancer conspicuity, while reducing the effects of local microscopic motion and magnetic field fluctuations.MethodsTen patients with biopsy‐proven prostate cancer were studied under an Institutional Review Board‐approved protocol. Individual acquisitions of DWI signal intensities were reconstructed to calculate inter‐acquisition distributions and their statistics, which were compared for healthy versus cancer tissue. A method was proposed to detect and filter the acquisitions affected by motion‐induced signal loss. First, signals that reflect restricted diffusion were separated from the acquisitions that suffer from signal loss, likely due to microscopic motion, by imposing a cutoff value. Furthermore, corrected apparent diffusion coefficient maps were calculated by employing a weighted sum of the multiple acquisitions, instead of conventional averaging. These weights were calculated by applying a soft‐max function to the set of acquisitions per‐voxel, making the analysis immune to acquisitions with significant signal loss, even if the number of such acquisitions is high.ResultsInter‐acquisition variation is much larger than the Rician noise variance, local spatial variations, and the estimates of diffusion anisotropy based on the current data, as well as the published values of anisotropy. The proposed method increases the contrast for cancers and yields a sensitivity of 98.8% with a false positive rate of 3.9%.ConclusionMotion‐induced signal loss makes conventional signal‐averaging suboptimal and can obscure signals from areas with restricted diffusion. Filtering or weighting individual acquisitions prior to image analysis can overcome this problem.

Fluid-Driven Instabilities in Granular Media: From Viscous Fingering and Dissolution Wormholes to Desiccation Cracks and Ice Lenses

Single and multi-phase fluids fill the pore space in sediments; phases may include gases (air, CH4, CO2, H2, and NH3), liquids (aqueous solutions or organic compounds), and even ice and hydrates. Fluids can experience instabilities within the pore space or trigger instabilities in the granular skeleton. Then, we divided fluid-driven instabilities in granular media into two categories. Fluid instabilities at constant fabric take place within the pore space without affecting the granular skeleton; these can result from hysteresis in contact angle and interfacial tension (aggravated in particle-laden flow), fluid compressibility, changes in pore geometry along the flow direction, and contrasting viscosity among immiscible fluids. More intricate fluid instabilities with fabric changes take place when fluids affect the granular skeleton, thus the evolving local effective stress field. We considered several cases: 1) open-mode discontinuities driven by drag forces, i.e., hydraulic fracture; 2) grain-displacive invasion of immiscible fluids, such as desiccation cracks, ice and hydrate lenses, gas and oil-driven openings, and capillary collapse; 3) hydro-chemo-mechanically coupled instabilities triggered by mineral dissolution during the injection of reactive fluids, from wormholes to shear band formation; and 4) instabilities associated with particle transport (backward piping erosion), thermal changes (thermo-hydraulic fractures), and changes in electrical interparticle interaction (osmotic-hydraulic fractures and contractive openings). In all cases, we seek to identify the pore and particle-scale positive feedback mechanisms that amplify initial perturbations and to identify the governing dimensionless ratios that define the stable and unstable domains. A [N/m] Contact line adhesion

An ultrasensitive bacteria biosensor using “multilayer cake” silver microelectrode based on local high electric field effect

A signal response mechanism of local high electric field effects was designed to detect bacteria using a chemically modified “multilayer cake” micro-nanostructured pillar electrode. Since the silver electrode has a strong specific electrochemical signal response to chloride ions, we choose silver as the electrode material. The microelectrode was prepared by a one-step localized electrochemical deposition method without the use of mold. Then the electrode was successively functionalized with chitosan, catechol, and aptamer. Many nano- and micro-scale protrusion tips on the electrode surface generated a local high electric field and drove the leakage of intracellular chloride ions when bacteria were captured by APT; thus, a reduced signal of the silver electrode related to chloride ions was recorded. A pseudocapacitor structure composed of chitosan, catechol, Ru3+, and Fc was constructed on an electrode surface to further amplify the signal. The electrochemical sensor based on this electrode showed excellent performance for template bacteria Staphylococcus aureus detection in terms of the detection limit (1 CFU mL−1), linear response range (1–105 CFU mL−1), and specificity. This work provides another way to design an electrochemical biosensor using the nanoeffect of the electrode rather than the conventional current response based on the electrical properties of the bacterial surface.

Nanophysics in modern medicine

WNanophysics is rapidly developing for the recent couple of decades. Unique physical properties of materials at the nanoscale are the reason for this rapid development. Ideas, materials and structures of nanophysics have found their wide application in related fields of modern science, including biology and medicine. This short review is devoted to the application of nanophysics in modern medicine. The main focus was on application of ideas and physical phenomena of nanophysics in oncology and antiviral therapy. We have focused on the use of nanosystems both for tumor imaging and for the struggle against some types of tumors. The use of nanoparticles as nanocontainers for targeted drug delivery was briefly discussed. We also demonstrated how the effects of nanophysics can be used to develop new non-traditional methods of antiviral therapy. The focus of these methods was the idea of physical (field) action of nanoparticles on the viruses, which is based on the local-field enhancement effect that is the reason of ponderomotive forces acting on the viruses up to destruction of viral envelopes.

Enhanced nonlinear absorptive behaviour of phenylcalix[4]resorcinarene-graphene oxide nanocomposite

Calix[4]resorcinarenes is a macrocyclic molecule that serves as a host for various metal ions and neutral molecules. The anisotropic nature of this molecule makes it attractive as a nonlinear optical material. Herein, we report the remarkable developments in nonlinear absorption and competent optical limiting action of noncovalently functionalized phenylcalix[4]resorcinarene (PCR) graphene oxide (GO) compared to its constituent compounds. The Fourier transform infrared spectrum, Raman spectrum, photoluminescence spectrum, and UV–Visible absorption spectrum of the composite (PCR-GO NC) reveal the modified optical properties of PCR. The nonlinear optical studies were investigated by z scan technique using Q switched Nd: YAG laser operating at 532 nm with 7 ns pulse width. Reverse saturable absorption primarily contributes to the absorptive nonlinearity of PCR and PCR-GO NC in the nanosecond regime. Compared to the bare PCR sample, an elevated nonlinear optical (NLO) response is observed for the nanocomposite (PCR-GO NC), and the enhancement factor in the absorptive nonlinearity is found to be 3.4. Moreover, the optical limiting behaviour of PCR-GO nanocomposite (limiting threshold value - 0.91 J/cm2) is highly impressive compared to many of the benchmark results, making it suitable for making laser safety devices that can protect the human eye and devices from laser-induced damages. The phenomenally enhanced NLO behaviour of the nanocomposite could be derived from the combined effect of nonlinear absorption, photoinduced charge transfer between PCR and GO, and the intensified local field effect produced by GO.

Upper crustal anisotropy in the Southeastern Sichuan Basin, China from shear-wave splitting measurements

The Sichuan basin which embodies salt and shale gas resources, is characterized by low seismicity. Seismicity in the southeastern Sichuan basin increased dramatically in recent years, including a series of moderate to strong earthquakes. We investigate seismic anisotropy in the upper crust by performing shear wave splitting analyses on local earthquakes recorded at seventeen stations around the Changning-Xingwen area, southeastern Sichuan basin between January 2016–February 2021. We perform an automatic shear wave splitting analysis and obtain 2926 high-quality splitting measurements by examining 5174 local earthquakes. The delay times range between 0.08 and 0.20 s, and the anisotropy magnitude ranges between 1.9% and 5.5% with a mean of 4.2%, indicating that the study area has significant strength of anisotropy. The fast polarization directions are highly variable reflecting a combined effect of complex local structure and stress field in this area. In the southeastern part of the study area, fast directions are aligned parallel to NW- and NE-oriented surface structures, suggesting structural anisotropy. In the northwestern part of the study area, fast-polarization directions align parallel to the strike of folds and the direction of maximum horizontal compressive stress, probably reflecting the combination of both stress- and structural-controlled anisotropy. Whereas at these stations of central part, fast directions tend to align parallel to the direction of maximum horizontal compressive stress, suggesting stress-induced anisotropy. We examined the temporal variation of seismic anisotropy associated with the 2019 MS 6.0 Changning earthquake. The significant changes in splitting parameters during the Changning earthquake period may only reflect the spatial changes in seismic anisotropy.

Morphology-Dependent One- and Two-Photon Absorption Properties in Blue Emitting CsPbBr3 Nanocrystals.

The linear and nonlinear optical parameters and morphologic dependence of CsPbBr3 nanocrystals (NCs) are crucial for device engineering. In particular, such information in asymmetric nanocrystals is still insufficient. We characterized the OPLA (σ1) and TPA cross sections (σ2) of a series CsPbBr3 nanocrystals with various aspect ratios (AR) using femtosecond transient absorption spectroscopy (TAS). The σ1 presents a linear volume dependence of all the samples, which agrees with the previous behavior in CsPbBr3 QDs. However, the σ2 values do not exhibit conventional power dependency of the crystal volume but are also modulated by the shape-dependent local field factors. In addition, the local field effect in CsPbBr3 NCs is contributed by their asymmetric morphologies and polar ionic lattices, which is more pronounced than in conventional semiconductor NCs. Finally, we revealed that the lifetimes of photogenerated multiexcitonic species of those nanocrystals feature identical morphology independence in both OPLA and TPA.

Second-Order Nonlinear Optical Responses of AlN Two-Dimensional Monolayer: A Real-Time First-Principles Study.

Two-dimensional materials have recently attracted attention due to their unique physical properties and promising applications. This work reports the electronic, linear and second-order nonlinear optical properties of aluminum nitride (AlN) monolayer by using a real-time first-principles approach based on Green's function theory. In this approach, quasi-particle corrections, crystal local field effects, and excitonic contributions are considered for investigating the linear and nonlinear responses. As a two-dimensional material with a wide direct gap of around 6.45 eV, the AlN monolayer exhibits strong resonances of absorption and second-harmonic spectra in the ultraviolet range. In the transparent spectral range from blue to deep ultraviolet (2.8-5.3 eV), strong peaks of second-order nonlinear susceptibility appear in the AlN monolayer with a large peak value of around 430 pm/V, which is one or two orders-of-magnitude larger than the nonlinear materials used in the ultraviolet range. The results presented in this work will find important applications for nonlinear imaging, spectroscopy, and nonlinear nanophotonics in the ultraviolet range.

Effect of laser ablated gold nanoparticles on the nonlinear optical properties of π-extended BODIPY dyes

Dipyrromethene boron difluoride (BODIPY) and its derivatives have attracted considerable interest due to their remarkable photophysical properties beneficial for developing fluorescent sensors, biolabels, photodynamic therapy agents, photonic materials, and so on. Herein, we report gold nanoparticles (AuNPs) induced modulation of nonlinear optical properties of π-extended BODIPY derivatives BPA and BDIPA. The spherical gold nanoparticles with an average particle size of 11 ± 3.5 nm were synthesized by pulsed laser ablation technique and characterized by transmission electron microscopy and dynamic light scattering. The interaction of AuNPs with the dye molecules was confirmed by UV/vis absorption and steady-state emission spectroscopy studies. Further, the dual-beam thermal lens technique was used to validate dye-nanoparticle interaction. The thermal diffusivity values of the samples at an excitation wavelength of 532 nm were measured and found that the overall heat diffusion was slower in the AuNPs added samples than that of the dye alone sample, corroborating dye-nanoparticle interaction. The third-order nonlinear optical absorption properties of the samples were investigated by using the Z-scan technique in the infrared region (1064 nm). The open aperture configuration shows significant reverse saturable absorption characteristics for all the samples. Determination of nonlinear absorption coefficient for the dye samples at different input intensities identified two-photon absorption as the important mechanism that produces reverse saturable absorption. The AuNPs incorporated dye samples showed a substantial enhancement in the nonlinear optical behavior. The nonlinear absorption coefficient of the AuNPs incorporated dye samples (10 cm/GW) was enhanced almost two times than that of dye alone samples (5 cm/GW). The enhanced nonlinearity is attributed to the intense local field effect of AuNPs.

Duality, decay rates, and local-field models in macroscopic QED

Any treatment of magnetic interactions between atoms, molecules, and optical media must start at the form of the interaction energy. This forms the base on which predictions about any number of magnetic atom-light properties stands, spontaneous decay rates and forces included. As is well known, the Heaviside-Larmor duality symmetry of Maxwell's equations, where electric and magnetic quantities are exchanged, is broken by the usual form of the magnetic interaction energy. We argue that this symmetry can be restored by including general local-field effects and that local fields should be treated as a necessity for correctly translating between the microscopic world of the dipole and the macroscopic world of the measured fields. This may additionally aid in resolving a long-standing debate over the form of the force on a dipole in a medium. Finally, we compute the magnetic dipole decay rate in a magnetodielectric with local-field effects taken into account and show that macroscopic quantum electrodynamics can be made to be dual symmetric at an operator level, instead of only for expectation values.

Evidence for a Local Field Effect in Surface Plasmon-Enhanced Sum Frequency Generation Vibrational Spectra

Surface plasmon-enhanced vibrational spectroscopy has been demonstrated to be an important highly sensitive diagnostic technique, but its enhanced mechanism is yet to be explored. In this study, we couple femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) with surface plasmon generated by the excitation of localized gold nanorods/nanoparticles and investigate the plasmonically enhanced factors (EFs) of SFG signals from poly(methyl methacrylate) films. Through monitoring the SFG intensity of carbonyl and ester methyl groups, we have established a correlation between EFs and the coupling of localized surface plasmon resonance with SFG and visible beams. It is found that the total enhanced factor is approximately proportional to the square of an enhanced factor of the SFG electromagnetic field and the fourth power of the enhanced factor of the visible electromagnetic field. The local field effect is roughly expressed to be the square of an enhanced factor of the visible electromagnetic field. This finding will help to guide the experimental design of plasmon-enhanced SFG to drastically improve the detection sensitivity and thus provide greater insight into the ultrafast dynamics near plasmonic surfaces.

Anomalous screening in narrow-gap carbon nanotubes

The screening of Coulomb interaction controls many-body physics in carbon nanotubes, as it tunes the range and strength of the force that acts on charge carriers and binds electron-hole pairs into excitons. In doped tubes, the effective Coulomb interaction drives the competition between Luttinger liquid and Wigner crystal, whereas in undoped narrow-gap tubes it dictates the Mott or excitonic nature of the correlated insulator observed at low temperature. Here, by computing the dielectric function of selected narrow- and zero-gap tubes from first principles, we show that the standard effective-mass model of screening systematically underestimates the interaction strength at long wavelength, hence missing the binding of low-energy excitons. The reason is that the model critically lacks the full three-dimensional topology of the tube, being adapted from graphene theory. As ab inito calculations are limited to small tubes, we develop a two-band model dielectric function based on the plane-wave expansion of Bloch states and the exact truncated Coulomb cutoff technique. We demonstrate that our -- computationally cheap -- approach provides the correct screening for narrow-gap tubes of any size and chirality. A striking result is that the screened interaction remains long-ranged even in gapless tubes, as an effect of the microscopic local fields generated by the electrons moving on the curved tube surface. As an application, we show that the effective electron-electron force that is felt at distances relevant to quantum transport experiments is super Coulombic.

Dielectric and optical properties of cubic perovskites ATiO[formula omitted] (A = Ca, Sr, Ba, Pb)

We study dielectric and optical properties of perovskites ATiO3 (A = Ca, Sr, Ba, Pb) in the cubic phase. The calculations are performed within the time-dependent density functional theory, including local field effects. The origin of absorption peaks is indicated based on the orbital-projected band structure. The theoretical calculations show that the perovskites have a plasmon mode at around 12 eV, which was not observed in experiments.

The Root Cause Behind a Peculiar Dual-Mode ON-State Breakdown in High Voltage LDMOS

This work investigates the often-observed current discontinuity much before avalanche breakdown (dual-mode ON-state breakdown) in the output characteristics of a laterally diffused metal–oxide–semiconductor (LDMOS) device. The physical origin of the dual-mode ON-state breakdown, often reasoned to be due to parasitic n-p-n, is shown to be independent of parasitic n-p-n. A laterally diffused tunnel FET (LDTFET) with a drift region profile same as LDMOS was experimented to rule out the effect of parasitic n-p-n. LDTFET device, which intrinsically cannot have parasitic n-p-n, also shows similar output characteristics with dual-mode ON-state breakdown. This proved that the parasitic bipolar turn-on is not the root cause behind the observed behavior. On the contrary, it was found to be dependent on the onset of space charge modulation (SCM) in the drift region, resulting in localized high electric field and quasi-saturation effects at low drain voltages. The effect of mobility degradation due to the high electric field in the drift region post-SCM is also presented, emphasizing that the observed behavior results from the high field mobility degradation of majority charge carriers.

First-principles calculations for transient absorption of laser-excited magnetic materials

We investigate the modification in the optical properties of laser-excited bulk cobalt and nickel using the time-dependent density functional theory at a finite electron temperature. As a result of the first-principles simulation, a complex change in the photoabsorption of the magnetic materials is observed around the M 2,3 absorption edge. Based on the microscopic analysis, we clarify that this complex absorption change consists of the two following components: (i) the decrease in the photoabsorption in a narrow energy range around the M 2,3 edge, which reflects the blue shift of the absorption edge due to the light-induced demagnetization, and (ii) the increase in the photoabsorption in a wider range around the M 2,3 edge, which reflects the modification in the local-field effect due to the light-induced electron localization. The relation between the transient optical and magnetic properties may open a way to monitor ultrafast (de)magnetization and spin dynamics in magnetic materials via transient absorption spectroscopy.