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The development of experimental techniques at the nanoscale has enabled the performance of spectroscopic measurements on single-molecule current-carrying junctions. These experiments serve as a natural intersection for the research fields of optical spectroscopy and molecular electronics. We present a pedagogical comparison between the perturbation theory expansion of standard nonlinear optical spectroscopy and the (non-self-consistent) perturbative diagrammatic formulation of the nonequilibrium Green's functions method (which is widely used in molecular electronics), highlighting their similarities and differences. By comparing the two approaches, we argue that the optical spectroscopy of open quantum systems must be analyzed within the more general Green's function framework. [ABSTRACT FROM AUTHOR]

Chiral active fluids can exhibit odd viscosity, a property that breaks the time-reversal and parity symmetries. Here, we examine the hydrodynamic flows of a rigid disk moving in a compressible 2D fluid layer with odd viscosity, supported by a thin lubrication layer of a conventional fluid. Using the 2D Green's function in Fourier space, we derive an exact analytical solution for the flow around a disk of arbitrary size, as well as its resistance matrix. The resulting resistance coefficients break the Onsager reciprocity, but satisfy the Onsager–Casimir reciprocity to any order in odd viscosity. [ABSTRACT FROM AUTHOR]

We introduce an alternative route to quasiparticle self-consistent GW calculations (qsGW) on the basis of a joint approximate diagonalization of the one-body GW Green's functions G ( ε n Q P ) taken at the input quasiparticle energies. Such an approach allows working with the full dynamical self-energy, without approximating the latter by a symmetrized static form as in the standard qsGW scheme. Calculations on the GW100 molecular test set lead, nevertheless, to a good agreement, at the 60 meV mean-absolute-error accuracy on the ionization potential, with respect to the conventional qsGW approach. We show further that constructing the density matrix from the full Green's function as in the fully self-consistent scGW scheme, and not from the occupied quasiparticle one-body orbitals, allows obtaining a scheme intermediate between the qsGW and scGW approaches, closer to coupled-cluster reference values. [ABSTRACT FROM AUTHOR]

We explore the impact of point defects, including oxygen vacancies (Ov), cerium interstitials (Ce-int), and hydroxyl groups (Hy), on the electronic and optical properties of bulk CeO2 using many-body Green's function theory (GW method and Bethe–Salpeter equation). Although these three defects all produce occupied electronic levels near the conduction band minimum, they impose quite different effects. Ov and Ce-int induce strong peaks in the low-energy region of the imaginary part of the microscopic dielectric function, indicating stronger electronic screening compared to the pristine CeO2. This causes pronounced narrowing of the bandgap, e.g., by 0.8 eV in G0W0 and 1.6 eV in the eigenvalue self-consistent GW for Ov. Comparatively, Hy affects little electronic screening and bandgap at different levels of GW calculations. For the lowest several 4f orbitals, the exchange part of the self-energy (|Σx| > 9 eV) in GW is much stronger than the correlation part (|Σc| < 5 eV) for Ov and Ce-int, while |Σc| is much stronger than |Σx| instead for the pristine CeO2 and Hy. Quasiparticle weights in Ov and Ce-int decrease by a large quantity compared to the pristine CeO2. Consideration of Ov and Ce-int might to some extent relieve the discrepancy between the GW bandgap of the pristine CeO2 and the experimental gap. Ov and Ce-int could reduce the excitonic binding energy several times and result in optical absorption, which corresponds to the experiments. [ABSTRACT FROM AUTHOR]

Single-Molecule Junctions (SMJs) are key platforms for the exploration of electron transport at the molecular scale. In this study, we present a method that employs different exchange-correlation density functionals for the molecule and the lead domains in an SMJ, enabling the selection of the optimal one for each part. This is accomplished using a formally exact projection-based density-functional theory (DFT-in-DFT) embedding technique combined with the non-equilibrium Green's function method to predict zero-bias conductance. The effectiveness of this approach is illustrated through transport calculations on SMJs with benzene-1,4-diamine and its tetramethylated and tetrafluorinated variants, using the CAM-B3LYP range-separated hybrid functional for the embedded molecule and the Perdew–Burke–Ernzerhof (PBE) functional for the electrodes. The findings indicate a substantial improvement in the accuracy of the predicted zero-bias conductance compared to traditional modeling using the PBE functional across the entire system. The causes for the noted improvement are demonstrated through the examination of alterations in the energy levels of the embedded molecule, along with variations in the electrode–molecule interactions. [ABSTRACT FROM AUTHOR]

Gaussian process regression is used to develop a model for predicting carrier transport in superlattice (SL) structures grown on GaSb and 6.2 Å substrates. This model is used to search SL structures optimized for enhanced hole transport in the vertical (growth) direction. Nonequilibrium Green's functions calculations are used to determine the vertical hole mobility of several chosen structures in both ideal and disordered cases. It is demonstrated that the conductivity effective mass can be used in some cases as a qualitative predictor for the relative hole mobility between different structures. However, in the case of disordered SLs, the effective mass must be calculated from quasi-random disordered structures as the results may differ significantly from the ideal case. Ultimately, a methodology for predicting SL structures optimized for high hole transport efficiency in the case of ideal and disordered SLs is demonstrated. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of a sample structure on the amplitude of time-domain Brillouin scattering (TDBS) oscillations using silicon wafers with different oxide layer thicknesses as an example. According to the calculation results based on transfer matrix theory and Green's function, along with experimental results, we discovered that the amplitude of TDBS exhibits dual peaks corresponding to the thickness of the silicon dioxide layer, highlighting the TDBS's acute sensitivity to an internal sample structure. Furthermore, our computational results indicate that both the roughness of the sample and the non-monochromatic nature of the probe light affect the time-domain Brillouin scattering signal, underscoring the significant role of interference effects in TDBS detection. The outcomes of this study suggest that by precisely designing the thickness of the transducer layer, the time-domain Brillouin scattering signal can be enhanced, and it may be possible to determine the roughness of the sample using the amplitude of the time-domain Brillouin oscillation. This is beneficial for improving the detection accuracy of time-domain Brillouin scattering and for extracting a broader range of physical information from TDBS oscillations. [ABSTRACT FROM AUTHOR]

Our research investigates the magnon bands and their topological characteristics in a ferromagnetic pyrochlore lattice, with the Dzyaloshinskii–Moriya (DM) interaction playing a significant role. Given its kagome AB bilayer structure, the ferromagnetic exchange couplings, which may differ among the AB triangles, are further considered for their implications on the system's magnetic properties. By employing the non-equilibrium Green's function method, we explicitly demonstrate that the one-way chiral edge magnon transport is indeed regulated by the DM interaction direction (D → − D) and the exchange interaction of J 1 and J 2 (J 1 ↔ J 2). Moreover, we demonstrate that the topological edge state predominantly resides along the edges and exhibits an oscillatory decay as it penetrates into the bulk in a non-equilibrium state. Although the chiral edge magnons and the corresponding energy current tend to travel along one edge from the hot region to the cold one, in the bulk, however, the energy current flows reversely from the cold to the hot region. The valley magnon Hall effects and chiral edge transport proposed here may be realized in the thin films of the insulating ferromagnet, such as Lu 2 V 2 O 7. Thus, it will pave the way for a more extensive use of magnonics in future technologies. [ABSTRACT FROM AUTHOR]

Computationally tractable and reliable, albeit approximate, methods for studying exciton transport in molecular aggregates immersed in structured bosonic environments have been actively developed. Going beyond the lowest-order (Born) approximation for the memory kernel of the quantum master equation typically results in complicated and possibly divergent expressions. Starting from the memory kernel in the Born approximation, and recognizing the quantum master equation as the Dyson equation of Green's functions theory, we formulate the self-consistent Born approximation to resum the memory-kernel perturbation series in powers of the exciton–environment interaction. Our formulation is in the Liouville space and frequency domain and handles arbitrary exciton–environment spectral densities. In a molecular dimer coupled to an overdamped oscillator environment, we conclude that the self-consistent cycle significantly improves the Born-approximation energy-transfer dynamics. The dynamics in the self-consistent Born approximation agree well with the solutions of hierarchical equations of motion over a wide range of parameters, including the most challenging regimes of strong exciton–environment interactions, slow environments, and low temperatures. This is rationalized by the analytical considerations of coherence-dephasing dynamics in the pure-dephasing model. We find that the self-consistent Born approximation is good (poor) at describing energy transfer modulated by an underdamped vibration resonant (off-resonant) with the exciton energy gap. Nevertheless, it reasonably describes exciton dynamics in the seven-site model of the Fenna–Matthews–Olson complex in a realistic environment comprising both an overdamped continuum and underdamped vibrations. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the properties of the recently proposed real-time equation-of-motion coupled-cluster (RT-EOM-CC) cumulant Green's function approach [Rehr et al., J. Chem. Phys. 152, 174113 (2020)]. We specifically focus on identifying the limitations of the original time-dependent coupled cluster (TDCC) ansatz and propose an enhanced double TDCC ansatz, ensuring the exactness in the expansion limit. In addition, we introduce a practical cluster-analysis-based approach for characterizing the peaks in the computed spectral function from the RT-EOM-CC cumulant Green's function approach, which is particularly useful for the assignments of satellite peaks when many-body effects dominate the spectra. Our preliminary numerical tests focus on reproducing, approximating, and characterizing the exact impurity Green's function of the three-site and four-site single impurity Anderson models using the RT-EOM-CC cumulant Green's function approach. The numerical tests allow us to have a direct comparison between the RT-EOM-CC cumulant Green's function approach and other Green's function approaches in the numerical exact limit. [ABSTRACT FROM AUTHOR]

Owing to charge free property, magnon is highly promising to achieve dissipationless transport without Joule heating and, thus, potentially applicable to energy efficient devices. In this paper, using the non-equilibrium Green's function, we present the bulk-boundary correspondence for magnonic Kagome lattices by studying the edge magnons transport. With staggered exchange interaction and Dzyaloshinskii–Moriya interaction in the Kagome lattices, one can observe valley contrasting magnon Hall effect, which endows magnon transport with the valley degree of freedom and adds a new dimension to regulate magnon excitation. In particular, we demonstrate that the valley splitting in the Kagome lattice enables a tunable single edge chiral transport. Thermal rectification is a direction-dependent asymmetric heat transfer phenomenon; here, we report the tunable thermal rectification by asymmetric nonlinear effect, and it is, indeed, regulated by the Dzyaloshinskii–Moriya interaction direction (D → − D) and the exchange of J 1 and J 2 (J 1 ↔ J 2). Moreover, we show that the topological edge state mainly localizes around edges and leaks into the bulk with oscillatory decay. These give full play to spin and valley degrees of freedom and provide various avenues for information encoding and manipulation based on valley related magnonic flux. [ABSTRACT FROM AUTHOR]

This article analytically explores defect assisted spin injection in organic magnetic tunnel junctions (MTJs) [x/rubrene/Co, x = La 2 O 3 , LaMnO 3 , La 0.7 Ca 0.3 MnO 3 (LCMO), La 0.7 Sr 0.3 MnO 3 (LSMO)] employing nonequilibrium Green's function (NEGF). Spin precession at ferromagnet (FM)/organic semiconductor (OSC) interface defect states have been considered while modeling the MTJ devices. Variations in voltage dependent parallel (R P) and antiparallel (R A P ) resistances have been attributed to modified spin dependent scattering at modified spin resolved density of states of magnetic electrodes. Moreover, change in distribution of defect state depths at a spin injection interface has also been observed to modify R P /R A P , and hence, tunnel magnetoresistance (TMR) across the devices. Localization of defect state distribution due to a high spin split band may have resulted in large TMR for La 2 O 3 devices. Nonlinear spin transfer torque (STT) in devices other than LSMO indicates compensation of spin damping, resulting in a high TMR response across the devices. Hence, the localization of defect state distribution and the choice of magnetic electrodes with high spin split bands may be exercised to realize spintronic devices for low power spin memory applications. [ABSTRACT FROM AUTHOR]

Chiral-induced-spin-selectivity of electron transport and its interplay with DNA's mechanical motion are explored in a double stranded DNA helix with spin–orbit-coupling. The mechanical degree of freedom is treated as a stochastic classical variable experiencing fluctuations and dissipation induced by the environment as well as force exerted by nonequilibrium, current-carrying electrons. Electronic degrees of freedom are described quantum mechanically using nonequilibrium Green's functions. Nonequilibrium Green's functions are computed along the trajectory for the classical variable taking into account dynamical, velocity dependent corrections. This mixed quantum-classical approach enables calculations of time-dependent spin-resolved currents. We showed that the electronic force may significantly modify the classical potential, which, at sufficient voltage, creates a bistable potential with a considerable effect on electronic transport. The DNA's mechanical motion has a profound effect on spin transport; it results in chiral-induced spin selectivity, increasing spin polarization of the current by 9% and also resulting in temperature-dependent current voltage characteristics. We demonstrate that the current noise measurement provides an accessible experimental means to monitor the emergence of mechanical instability in DNA motion. The spin resolved current noise also provides important dynamical information about the interplay between vibrational and spin degrees of freedom in DNA. [ABSTRACT FROM AUTHOR]

Motivated by the booming development of spintronics based on quantum dot systems, we employed the standard nonequilibrium Green's function theory to derive the transport formula and the heat generation formula of a quantum dot coupled to a substrate and study the relation between spin current and its accompanying heating or cooling. Our results demonstrate that (i) a thermal bias combined with Zeeman splitting can generate steady spin current in a limited dot level range, while a rotating magnetic field can generate time-average spin current in a global range and pure spin current can induce more heat generation than non-pure spin current; (ii) magnetic resonance of spin current can also effectively enhance heat generation; (iii) appropriate environmental temperature in conjunction with a thermal bias makes cooling, while increasing the frequency of the rotating magnetic can easily give rise to the transition from cooling to heating; and (iv) enhancing the coupling between quantum dots and substrates can effectively reduce heat generation while maintaining the fundamental properties of pure spin current. [ABSTRACT FROM AUTHOR]

We present a simple implicit solution for the time-dependent trajectory of a thin Asay foil ejecta diagnostic for the general case where the impinging ejecta cloud is generated by a source function characterized by an arbitrary (sustained) time dependence and a time-independent (stationary) particle velocity distribution. In the limit that the source function time dependence becomes a delta function, this solution—which is amenable to rapid numerical calculations of arbitrary accuracy—exactly recovers a previously published solution for the special case of instantaneous ejecta production. We also derive simple expressions for the free-surface arrival (catch-up) time as well as the true ejecta areal mass accumulation on the accelerating foil and place bounds on the level of error incurred when applying instant-production mass solutions to a sustained-production trajectory. We demonstrate these solutions with example calculations for hypothetical source functions spanning a wide range of ejecta production durations, velocity distributions, and temporal behaviors. These calculations demonstrate how the foil trajectory is often insensitive to the temporal dependence of the source function, instead being dominated by the velocity distribution. We quantify this insensitivity using a "compatibility score" metric. Under certain conditions, one may capitalize upon this insensitivity to obtain a good approximation of the second integral of the velocity distribution from the observed foil trajectory. [ABSTRACT FROM AUTHOR]

Exploring potential two-dimensional monolayers with large photogalvanic effect (PGE) has been of great importance for developing self-powered optoelectronic devices. In this paper, we systematically investigate the generation of PGE photocurrent in chalcogen-based Janus XYZ monolayers (X/Y/Z = S, Se, Te; X ≠ Y ≠ Z) based on non-equilibrium Green's function formalism with density functional theory. The optimized Janus SSeTe, SeSTe, and TeSeS monolayers in the rectangular phase are shown stable and, respectively, possess 1.54, 1.49, and 1.74 eV indirect bandgaps. Illuminated by linearly polarized light, the PGE photocurrent without bias voltage can be collected in both armchair and zigzag directions. Unlike common Janus 2D materials with C3v symmetry, the photocurrent peak values of Janus XYZ monolayers do not come up with certain polarization angles, while the relations can be fitted by Iph = α sin(2θ) + β cos(2θ) + γ at each photon energy. Meanwhile, the maximum photoresponses of Janus SSeTe, SeSTe, and TeSeS monolayers are 2.02, 3.33, and 4.42 a20/photon, respectively. The relatively large PGE photocurrents and complicated polarization relations result from the lower symmetry of Janus XYZ monolayers. Moreover, the specific polarization angles for maximum photoresponses at each photon energy and the ratio between two transport directions are demonstrated, reflecting the anisotropy. Our results theoretically predict a potential Janus monolayer family for self-powered optoelectronic applications. [ABSTRACT FROM AUTHOR]

The ferroelectric tunneling junctions (FTJs) are widely recognized as one of the non-volatile memories with significant potential. Ferroelectricity usually fades away as materials are thinned down below a critical value, and this problem is particularly acute in the case of shrinking device sizes, thus attracting attention to two-dimensional ferroelectric materials (2DFEMs). In this work, we designed 2D ferroelectric Ga2O3-based FTJs with out-of-plane polarization, and the influence of metal–semiconductor contact in the electrode region on the system is considered. Here, using density functional theory combined with the non-equilibrium Green's function approach to quantum transport calculations, we demonstrate robust ferroelectric polarization-controlled switching behavior between metallic and semiconducting states in Ga2O3/WS2 ferroelectric heterostructures. The potential barrier of the metal–semiconductor contact in the electrode region is lower than that of the intrinsic material, thereby resulting in an increased probability of electron tunneling. Our results reveal the crucial role of 2DFEMs in the construction of FTJs and highlight the significant impact of electrode contact types on performance. This provides a promising approach for developing high-density ferroelectric memories based on 2D ferroelectric semiconductor heterostructures. [ABSTRACT FROM AUTHOR]

We present a semi-analytical treatment of the spontaneous emission enhancement for collective lattice resonances of a linear 1D array of metallic nanoparticles in order to improve the physical understanding of these resonances, previously explored numerically. The treatment is based on the coupled-dipole approximation and Green's function formalism. We calculate the Purcell factor of the surface lattice resonance for localized emitters as a function of emitter position and compare it to the resonant enhancement for a localized plasmonic resonance of an isolated single nanoparticle. We find that the Purcell factor for a single emitter (or an incoherent ensemble of emitters) near the nanoparticle is typically smaller for the surface lattice resonance, although it can be higher for emitters nearly halfway between the particles. Nevertheless, in agreement with previous models, the lattice resonances display stronger emission in certain regions as well as a much narrower range of emission angles, which can lead to improved collection efficiency. Finally, we show that the "slow-propagating" modes of square 2D lattices of nanoparticles are capable of significantly stronger Purcell-enhanced emission. [ABSTRACT FROM AUTHOR]

A plethora of biological, physical, and chemical phenomena involve transport of charged particles (ions). Its continuum-scale description relies on the Poisson–Nernst–Planck (PNP) system, which encapsulates the conservation of mass and charge. The numerical solution of these coupled partial differential equations is challenging and suffers from both the curse of dimensionality and difficulty in efficiently parallelizing. We present a novel particle-based framework to solve the full PNP system by simulating a drift–diffusion process with time- and space-varying drift. We leverage Green's functions, kernel-independent fast multipole methods, and kernel density estimation to solve the PNP system in a meshless manner, capable of handling discontinuous initial states. The method is embarrassingly parallel, and the computational cost scales linearly with the number of particles and dimension. We use a series of numerical experiments to demonstrate both the method's convergence with respect to the number of particles and computational cost vis-à-vis a traditional partial differential equation solver. [ABSTRACT FROM AUTHOR]

A preceding paper [M. Dhar, J. A. Dickinson, and M. A. Berg, J. Chem. Phys. 159, 054110 (2023)] shows how to remove additive noise from an experimental time series, allowing both the equilibrium distribution of the system and its Green's function to be recovered. The approach is based on nonlinear-correlation functions and is fully nonparametric: no initial model of the system or of the noise is needed. However, single-molecule spectroscopy often produces time series with either photon or photon-counting noise. Unlike additive noise, photon noise is signal-size correlated and quantized. Photon counting adds the potential for bias. This paper extends noise-corrected-correlation methods to these cases and tests them on synthetic datasets. Neither signal-size correlation nor quantization is a significant complication. Analysis of the sampling error yields guidelines for the data quality needed to recover the properties of a system with a given complexity. We show that bias in photon-counting data can be corrected, even at the high count rates needed to optimize the time resolution. Using all these results, we discuss the factors that limit the time resolution of single-molecule spectroscopy and the conditions that would be needed to push measurements into the submicrosecond region. [ABSTRACT FROM AUTHOR]

As a newly synthesized two-dimensional (2D) carbon material, monolayer quasi-hexagonal phase fullerene (qHP C60) has an excellent electronic structure and low thermal conductivity. qHP C60 attracted significant attention from scientists because it has potential applications in thermoelectric materials. Thermoelectric properties of 2D materials significantly depend on the transport of carriers (such as electrons and phonons), and strain engineering is an essential method for modulating the transport of electrons and phonons in 2D materials. However, the strain engineering method for the modulation of the thermoelectric properties of monolayer qHP C60 has not been reported yet. In the present paper, the first-principles combined with the non-equilibrium Green's function method are used to investigate the ballistic transport properties of electrons and phonons in monolayer qHP C60. The effects of temperature, chemical potential, and biaxial tensile strain on the thermoelectric transport parameters (including conductivity, Seebeck coefficient, power factor, and thermal conductivity) as well as the figure of merit (ZT) of monolayer qHP C60 are presented, compared, discussed, and analyzed. We found that monolayer qHP C60 exhibits anisotropic characteristics in electron and phonon transport properties, showcasing outstanding thermoelectric properties. The distinctive quasi-hexagonal phase fullerene network structure offers a novel platform for exploring innovative 2D thermoelectric materials in research. This study provides crucial theoretical insights to guide the designing and implementation of 2D thermoelectric materials based on fullerenes. [ABSTRACT FROM AUTHOR]

This study explores the enhancement of thermoelectric response in a zigzag chain through irradiation with arbitrarily polarized light. The irradiation induces changes in hopping strengths, creating an asymmetric transmission profile around the Fermi energy, which is a crucial factor for achieving a higher figure of merit (FOM). Specific light configurations result in an FOM exceeding unity. We employ the Floquet–Bloch ansatz and minimal coupling scheme to model the irradiation effect, with transport properties evaluated using Green's function technique within the Landauer–Büttiker formalism. The investigation covers electrical conductance, thermopower, and thermal conductance due to electrons and phonons. Our research deepens understanding and opens avenues for tailoring nanostructures to fine-tune thermoelectric properties, advancing highly efficient energy conversion devices exploiting irradiation effects. [ABSTRACT FROM AUTHOR]

In this manuscript, carrier transport simulation methods are proposed for devices with the coexistence of quantum transport and diffusive transport by combining the nonequilibrium Green's function method with the drift-diffusion transport simulation method. Current continuity between quantum transport and drift-diffusion transport is ensured by setting quantum transport current as the connection boundary condition of drift-diffusion simulation or by introducing quantum transport-induced carrier generation rates to drift-diffusion simulation. A comprehensive study of our method and the method combining the Wentzel–Kramers–Brillouin (WKB) method with the drift-diffusion transport simulation method is performed for n-type tunnel oxide passivating contact solar cell to investigate their applicable conditions and balance the accuracy and computational cost. As the oxide barrier width, barrier height, and electron effective mass increase, or the doping concentration in the electron transport layer decreases to the extent that the blocking effect of the oxide barrier on light-generated electrons becomes significant, method I is more accurate since the transmission coefficient near the conduction band edge calculated by WKB is overestimated; otherwise, method II is more suitable due to its low computational cost without the loss of accuracy. In addition, the differences between current densities, carrier densities, and Shockley–Read–Hall recombination rates simulated under the two current continuity conditions for the solar cell with different carrier mobilities are also further explored and analyzed. [ABSTRACT FROM AUTHOR]

The time-periodic modulation of a temperature gradient can alter the heat transport properties of a physical system. Oscillating thermal gradients give rise to behaviors such as modified thermal conductivity and controllable time-delayed energy storage that are not present in a system with static temperatures. Here, we examine how the heat transport properties of a molecular lattice model are affected by an oscillating temperature gradient. We use analytical analysis and molecular dynamics simulations to investigate the vibrational heat flow in a molecular lattice system consisting of a chain of particles connected to two heat baths at different temperatures, where the temperature difference between baths is oscillating in time. We derive expressions for heat currents in this system using a stochastic energetics framework and a nonequilibrium Green's function approach that is modified to treat the nonstationary average energy fluxes. We find that emergent energy storage, energy release, and thermal conductance mechanisms induced by the temperature oscillations can be controlled by varying the frequency, waveform, and amplitude of the oscillating gradient. The developed theoretical approach provides a general framework to describe how vibrational heat transmission through a molecular lattice is affected by temperature gradient oscillations. [ABSTRACT FROM AUTHOR]

The non-equilibrium Green's function (NEGF) and quantum master equation (QME) are two main classes of approaches for electronic transport. We discuss various Floquet variances of these formalisms for transport properties of a quantum dot driven via interaction with an external periodic field. We first derived two versions of the Floquet NEGF. We also explore an ansatz of the Floquet NEGF formalism for the interacting systems. In addition, we derived two versions of Floquet QME in the weak interaction regime. With each method, we elaborate on the evaluation of the expectation values of the number and current operators. We examined these methods for transport through a two-level system that is subject to periodic driving. The numerical results of all four methods show good agreement for non-interacting systems in the weak regime. Furthermore, we have observed that circular light can introduce spin current. We expect these Floquet quantum transport methods to be useful in studying molecular junctions exposed to light. [ABSTRACT FROM AUTHOR]

Understanding the electronic transport properties of low-dimensional devices has increased dramatically in recent decades, especially for those with a promising future for application in nanotechnology. Among these nanoscopic systems are molecular systems, particularly organic molecules such as catechol, representing the small piece of a potential conductor assembled through larger biomolecules and inserted between two or more metal contacts. In this work, we present a theoretical description of the electronic transport of catechol, based on its π -conjugated aromatic system, under an external magnetic field stimulus, which is transverse to the alignment of the molecule. Thus, we analyze catechol's spintronic properties through the magnetoresistance generated by this field. We model the molecule using a tight-binding Hamiltonian and Green's functions; the transmission probability is calculated by means of the Fisher-Lee relation, and the characteristic current–voltage, spin polarization, and magnetoresistance curves based on Landauer's approach for two linking models of catechol to the metallic contacts. The results suggest a strong dependence on the spin direction of the charge carriers and the Zeeman energy (E z) on the Fermi level, generating a switch-like mechanism going from conducting to semiconducting material. This behavior opens a potential application of these catechol-based systems in future spintronic devices. [ABSTRACT FROM AUTHOR]

We study a moving adsorbate interacting with a metal electrode immersed in a solvent using the time-dependent Newns–Anderson–Schmickler model Hamiltonian. We have adopted a semiclassical trajectory treatment of the adsorbate to discuss the electron and energy transfers that occur between the adsorbate and the electrode. Using Keldysh Green's function scheme, we found a non-adiabatically suppressed electron transfer caused by the motion of the adsorbate and coupling with bath phonons that model the solvent. The energy is thus dissipated into electron–hole pair excitations, which are hindered by interacting with the solvent modes and facilitated by the applied electrode potential. The average energy transfer rate is discussed in terms of the electron friction coefficient and given an analytical expression in the slow-motion limit. [ABSTRACT FROM AUTHOR]

Terahertz (THz) quantum cascade lasers (QCLs) are technologically important laser sources for the THz range but are complex to model. An efficient extended rate equation model is developed here by incorporating the resonant tunneling mechanism from the density matrix formalism, which permits to simulate THz QCLs with thick carrier injection barriers within the semi-classical formalism. A self-consistent solution is obtained by iteratively solving the Schrödinger–Poisson equation with this transport model. Carrier–light coupling is also included to simulate the current behavior arising from stimulated emission. As a quasi-ab initio model, intermediate parameters, such as pure dephasing time and optical linewidth, are dynamically calculated in the convergence process, and the only fitting parameters are the interface roughness correlation length and height. Good agreement has been achieved by comparing the simulation results of various designs with experiments, and other models such as density matrix Monte Carlo and non-equilibrium Green's function method that, unlike here, require important computational resources. The accuracy, compatibility, and computational efficiency of our model enable many application scenarios, such as design optimization and quantitative insights into THz QCLs. Finally, the source code of the model is also provided in the supplementary material of this article for readers to repeat the results presented here, investigate, and optimize new designs. [ABSTRACT FROM AUTHOR]

High Chern number topological insulators can be obtained in a film of layered magnetic block system theoretically and experimentally. With nonzero Chern numbers, Chern insulators become valuable for fundamental topological physics and for improving next-generation electronic devices. We study energy and angular momentum radiation from layered topological insulators using the Dirac Fermion approach and by Green's function method. We make a connection between radiation magnitude and topological phase transitions. We find that the magnetic exchange field, intra-layer coupling, and inter-layer interaction are efficient measures to modify the energy radiation of layered topological materials. Moreover, the magnetic exchange field is indispensable for emitting angular momentum due to the need for breaking time-reversal symmetry. [ABSTRACT FROM AUTHOR]

Dielectric interfaces are crucial to the behavior of charged membranes, from graphene to synthetic and biological lipid bilayers. Understanding electrolyte behavior near these interfaces remains a challenge, especially in the case of rough dielectric surfaces. A lack of analytical solutions consigns this problem to numerical treatments. We report an analytic method for determining electrostatic potentials near curved dielectric membranes in a two-dimensional periodic "slab" geometry using a periodic summation of Green's functions. This method is amenable to simulating arbitrary groups of charges near surfaces with two-dimensional deformations. We concentrate on one-dimensional undulations. We show that increasing membrane undulation increases the asymmetry of interfacial charge distributions due to preferential ionic repulsion from troughs. In the limit of thick membranes, we recover results mimicking those for electrolytes near a single interface. Our work demonstrates that rough surfaces generate charge patterns in electrolytes of charged molecules or mixed-valence ions. [ABSTRACT FROM AUTHOR]

Gallenene is a novel metallic 2D material that can provide a semiconducting counterpart if patterned into quasi-one-dimensional (quasi-1D) nanostructures, i.e., gallenene nanoribbons (GaNRs). We investigate semiconducting GaNRs as a potential channel material for future ultrascaled field-effect transistors (FETs) by employing quantum transport simulations based on Green's functions and tight-binding Hamiltonians with the orbital resolution calibrated on ab initio calculations. The impact of GaNR width downscaling from ∼6 nm down to ∼0.2 nm on the electronic, transport, and ballistic device properties is investigated for the FET channel length of 15 nm. We report current enhancement and injection velocity overshoot effects for sub-1.2 nm-wide nFETs and pFETs, with a maximum current increase of 53% in the 1.2 nm-wide GaNR pFET in comparison to the widest device. In addition, promising current-driving capabilities of n- and p-channel GaNR FETs are observed with top ballistic currents of more than 2.2 mA/μm and injection velocities of up to 2.4 × 107 cm/s. The reported data are explained by analyzing the evolution of band structure and related parameters such as injection velocity, quantum capacitance, effective transport mass etc., with increasing quantum confinement effects in ultranarrow GaNRs. Generally, we find that quasi-1D gallenene is a promising channel material for future nanoscale FETs, especially for transistor architectures based on stacked nanosheets. [ABSTRACT FROM AUTHOR]

Negative differential resistance (NDR) is observed in various emerging electronic devices. As compared to the conventional silicon-based field effect transistor (FET), the NDR is widely investigated in two-dimensional (2D) transition metal dichalcogenide (TMD) FETs. In this work, we study the NDR effect for the TMD-based metal-edge-contact MoS 2 double-gate FET with 10 nm channel length. The multiscale atomistic simulation is demonstrated for the lateral heterostructure of a metal–semiconductor–metal FET by density functional theory, maximally localized Wannier function tight-binding Hamiltonian, and non-equilibrium Green's function methods. The quantum transport model in the given lateral heterostructure resulted in NDR in a double-gate FET. Here, we focus on the NDR by the systematic study of the transmission spectrum of the metal-edge-contact MoS 2 channel FET and finally compare it with zero NDR ideal highly doped FET. The peak-to-valley ratio in the NDR response can be modulated with the change in the gate-to-source voltage and can be used to explore various future electronic applications. [ABSTRACT FROM AUTHOR]

The band-anticrossing (BAC) model provides the basis for the self-consistent Green's function method that we have previously developed to calculate the density of states of GaN x As 1 − x dilute nitride alloys. In this paper, we extend this Green's function method to include the complex energy states and to find the poles of the Green's function, thereby allowing one to calculate the dispersion relation, group velocity, and the carrier decay rate in disordered dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the conventional two-band BAC model, which assumes that all N states are located at the same energy, and (2) a model which includes N states distributed over a range of energies, as expected in actual dilute nitride samples. Our results for the second model show a much shorter carrier mean-free path, and lower carrier mobility for GaN x As 1 − x , with the magnitude of the calculated mobility in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

In this work, we investigate the possibilities of performing charge and spin current rectifications using graphene nano-ribbon in the presence of Rashba spin–orbit (SO) interaction. More specifically, we explore the specific role of mechanical strain on these two different types of current rectifications. The system is simulated by a tight-binding framework, where all the results are worked out based on the standard Green's function formalism. In order to have current rectification, an asymmetry is required, which is incorporated through uncorrelated disorder among the constituent lattice points. From our extensive numerical analysis, we find that reasonably large charge and spin current rectifications can be obtained under strained conditions, and all the physical pictures are valid for a broad range of tight-binding parameters. The rectification properties are studied mostly for zigzag graphene nano-ribbons; however, an armchair ribbon is also taken into account for a clear comparison. Our work may provide a new direction of getting strain-controlled current rectifications in similar kinds of other physical systems as well. [ABSTRACT FROM AUTHOR]

In quantum chemical calculations of heterogeneous structures in solids, e.g., when an impurity is located on the surface, the conventional cluster model is insufficient to describe the electronic structure of substrates due to its finite size. The open-boundary cluster model (OCM) overcomes this problem by performing cluster calculations under the outgoing-wave boundary condition. In this method, a complex absorbing potential (CAP) is used to impose the boundary condition, but the CAP used in the previous studies required parameter optimization based on the complex variational principle. This study proposes and applies a parameter-free CAP to OCM calculations. This approach makes it possible to uniquely determine the band-specific CAP based on the surface Green's function theory. Using this CAP, we conducted OCM calculations of the tight-binding model of a one-dimensional semi-infinite chain, and we found that the calculated density of states agreed with the exact one. Surface states of the Newns–Anderson–Grimley model were also computed using the CAP, and the projected density of states on the adsorbed atom was successfully reproduced. [ABSTRACT FROM AUTHOR]

We present an atomistic simulation of thermoelectric properties in cove-edged graphene nanoribbons (CGNRs) via the nonequilibrium Green's function. Different from gapless zigzag graphene nanoribbons (ZGNRs), CGNRs exhibit a noticeable bandgap. Such a bandgap can be modulated by varying three structural parameters (namely, the width N, the distance between adjacent coves m, as well as the shortest offset n) of CGNRs, which can give rise to the transition from semiconducting to semi-metallic. Due to the less dispersive phonon bands and the decrease in the number of phonon channels of CGNRs, they are found to have the lower phonon thermal conductance than ZGNRs. Modulation of CGNRs can produce over tenfold improvement of the maximum of ZT compared to ZGNRs. This improvement is due to the promotion of the Seebeck coefficient together with the degradation of the phonon thermal conductance of CGNRs compared to ZGNRs. [ABSTRACT FROM AUTHOR]

The paper investigated the approximate solution of the extended Fisher–Kolmogorov. For this, an advanced approach: the improved quintic B-spline collocation technique has been employed, which is an enhancement over the conventional B-spline collocation method. The B-spline interpolant of degree five has been refined through the posteriori corrections, leading to the development of the improved B-spline solution. This proposed technique demonstrates superior convergence compared to the standard B-spline method, as assessed both theoretically and numerically. In tackling the extended Fisher–Kolmogorov equation, the space discretization is conducted using the improved quintic B-spline collocation methodology (IQSCM), and for the temporal domain discretization, the Crank-Nicolson scheme is applied. The error bounds and convergence analysis is established using the Green's functions. Von-Neumann stability analysis is carried out to discuss the stability of the technique. A few examples are solved and are represented graphically which helps in determining the nature of the solution. Also, $ L_{2} $ L 2 , $ L_{\infty } $ L ∞ error norms, and order of convergence are calculated to demonstrate the contribution of the new improved technique over the standard spline collocation technique. [ABSTRACT FROM AUTHOR]

The calculation of synthetic seismograms for global centroid moment tensor (GCMT) inversions relies on advanced 3-D Earth models. However, use of the path-average approximation for mode summation and surface-wave ray theory limits the method's accuracy. This can cause incorrect predictions of ground motion amplitude and polarization, and other unaccounted-for effects, which can bias the estimated earthquake parameters. To address this issue, we have developed a new and efficient way to calculate, store and access high-fidelity, long-period synthetic seismograms for state-of-the-art 3-D tomographic Earth models. We adapted the spectral-element wave-equation solver SPECFEM3D_GLOBE to generate a data base of Green functions on a global, sparse spectral-element grid of hypocenters for a large set of 180 station locations, using source–receiver reciprocity to speed up the calculation. The seismograms are organized and stored in a format that facilitates rapid access to a particular source region and stations of the Global Seismographic Network. Seismograms for any centroid location can be calculated efficiently via spatial interpolation without losing accuracy compared to full forward calculation. As a proof-of-concept, we perform |$\sim$| 9000 CMT inversions using the Sawade et al. approach, with GCMT solutions as starting models and without restriction on the number of iterations. Although the location updates are consistent with Sawade et al. we find a reduction in non-double-couple components in all types of events except for shallow strike-slip events. Given these encouraging results for future routine implementation, we present a first test and an outlook for routine 3-D GCMT analysis. [ABSTRACT FROM AUTHOR]

Rocks near a fault plane are commonly damaged by multiple earthquake ruptures, forming damage zones. The damage zone is an important structure controlling various properties of a fault, yet its fine scale (tens to hundreds of meters) structure is difficult to resolve with surface seismic observations. We propose to use earthquakes that occur at depth within a fault zone as virtual seismometers (VSs) and use surface observations to extract Green's function (GFs) between VS pairs (VSGFs). This method resembles that of ambient noise tomography and the retrieved VSGFs are related to the structures between event pairs. In this study, we develop the theory about how to extract VSGFs using surface stations deployed across a fault zone. First, we use a half-space model and Fresnel zone analysis to determine the upper and lower limits of the GF frequency band, which is controlled by the station spacing and aperture of a given seismic array. Then, for VS in a fault zone, we demonstrate that the VSGF can be retrieved by linear seismic arrays deployed across the fault, and that the VSGF is equivalent to waves emitted simultaneously from an array of mirror sources of one event and received by the other. Secondly, the half-space result is directly adopted to determine the corresponding frequency band in the damage zone situation. Thirdly, we analyse different combinations of VS pair geometry and conclude that a relatively larger VS distance (much larger than the damage zone width) is more effective to recover damage zone structures for the available frequency bands. In this situation, VSGFs are trapped waves, that is represented by the interference of mirror sources. In such a case, the trapped waves are equivalent to surface waves, which have dispersion features to extract damage zone structures. Finally, we adopt the VSGF method to the Ridgecrest earthquake aftershock monitoring array and use a profile of aftershocks to extract six pairs of VSGFs. The spatial variation of VSGFs may reflect the depth-dependent variation of damaged zone. Our analysis shows a promising direction to use VSGFs to extract spatial variations of fault damaged zones. [ABSTRACT FROM AUTHOR]

In the present work, first-principle thermoelectric property investigations of pristine and defective α-graphyne nanoribbons (α-GYNRs) are conducted. Investigations have also been extended toward variation in temperature affecting the thermoelectric properties. Other objectives of the work presented are to investigate the thermoelectric properties at three temperatures, 300K, 500K, and 700K, of a single vacancy defect in a carbon atom removed from α-GYNRs. Pristine α-GYNRs is an intrinsic band gap semiconductor since defects occur naturally during synthesis, and the band gap significantly increases due to single vacancies and removal of carbon atoms at different positions. It results in a change of electrical conductivity Seebeck coefficient, and thermal conductivity. For some defective structures, with increasing temperature, the Seebeck coefficient increases compared with that of the pure structure and decreases. Also, the total thermal conductivity increases with increasing temperature. The obtained results show that the figure-of-merit value of defective α-GYNRs is much better than pristine α-GYNRs. In addition, ZT decreases in different structures by increasing temperature. Among all the considered structures, the Seebeck coefficient values and the ZT of some defective structures reach about 1.18 and 2.5 times that of the pristine structures at room temperature, respectively. [ABSTRACT FROM AUTHOR]

A case study of seismic interferometry applied to a small microseismic monitoring network is here presented. The main objectives of this study are (i) to quantify the lateral variability of shear-wave velocities in the studied area, and (ii) to investigate the bias produced by noise directionality and nonstationarity in the velocity estimate. Despite the limited number of stations and the short-period character of the seismic sensors, the empirical Green's functions were retrieved for all station pairs using two years of passive data. Both group and phase velocities were derived, the former using the widespread frequency-time analysis, the latter through the analysis of the real part of the cross-spectra. The main advantage of combining these two methods is a more accurate identification of higher modes, resulting in a reduction of ambiguity during picking and data interpretation. Surface wave tomography was run to obtain the spatial distribution of group and phase velocities for the same wavelengths. The low standard deviation of the results suggests that the sparse character of the network does not limit the applicability of the method, for this specific case. The obtained maps highlight the presence of a lower velocity area that extends from the centre of the network towards southeast. Group and phase velocity dispersion curves have been jointly inverted to retrieve as many shear-wave velocity profiles as selected station pairs. While the average model can be used for a more accurate location of the local natural seismicity, the associated standard deviations give us an indication of the lateral heterogeneity of seismic velocities as a function of depth. Finally, the same velocity analysis was repeated for different time windows in order to quantify the error associated to variations in the noise field. Errors as large as 4% have been found, related to the unfavorable orientation of the receiver pairs with respect to strongly directional noise sources, and to the very short time widows. It was shown that using a one-year time window these errors are reduced to 0.3%. [ABSTRACT FROM AUTHOR]

Appropriate and precise selective sensing of highly reactive materials, especially nitroaromatic explosives, is critical for various essential security applications, such as airport security screening and strengthening homeland security. Detection of these compounds can be substantially improved with the advent of new nanoscale systems, such as two-dimensional materials. Among these materials, graphene stands out due to its excellent physical properties, attracting significant interest from researchers in several areas, and especially those related to real-world nanodevice applications. In this work, density functional theory along with a non-equilibrium Green's function scattering approach has been used to examine the capability of graphene for selective sensing of single molecules. It was found that both graphene nanosheets and graphene nanodevices can be used for discriminative detection of four types of explosive molecules: 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, tetryl, and picric acid. The results show that each explosive molecule affects the electronic properties of graphene differently, producing characteristic and unique features in the density of states and the electronic transport properties. In particular, the addition of explosive molecules leads, on the one hand, to the opening of an energy gap around the Fermi energy (EF) and to the emergence of peaks in the density of states, especially below the Fermi energy, and, on the other hand, to dips in the electronic transmission. Moreover, the presence of the explosive molecules also gives rise to an enhancement of the Seebeck coefficient (S), which can be used as well for discriminating between the targeted molecules. These results corroborate that it would be feasible to design and manufacture graphene-based nanosensors to discriminate between different types of compounds, particularly between explosive molecules which could have significant implications in the design of new security applications. [ABSTRACT FROM AUTHOR]

We show existence, uniqueness and positivity for the Green's function of the operator (Δ g + α) k in a closed Riemannian manifold (M , g) , of dimension n > 2 k , k ∈ N , k ≥ 1 , with Laplace-Beltrami operator Δ g = − div g (∇ ⋅) , and where α > 0. We are interested in the case where α is large: We prove pointwise estimates with explicit dependence on α for the Green's function and its derivatives. We highlight a region of exponential decay for the Green's function away from the diagonal, for large α. [ABSTRACT FROM AUTHOR]

This work introduces a novel method for estimating hydrological loading displacement using 3D Convolutional Neural Networks (3D-CNN). This approach utilizes vertical displacement time series data from 41 Global Navigation Satellite System (GNSS) stations across Yunnan Province, China, and its adjacent areas, coupled with spatiotemporal variations in terrestrial water storage derived from the Gravity Recovery and Climate Experiment satellites (GRACE). The 3D-CNN method demonstrates markedly higher inversion precision compared to conventional load Green's function inversion techniques. This improvement is evidenced by substantial reductions in deviations from GNSS observations across various statistical metrics: the maximum deviation decreased by 1.34 millimeters, the absolute minimum deviation by 1.47 millimeters, the absolute mean deviation by 79.6%, and the standard deviation by 31.4%. An in-depth analysis of terrestrial water storage and loading displacement from 2019 to 2022 in Yunnan Province revealed distinct seasonal fluctuations, primarily driven by dominant annual and semi-annual cycles, and these periodic signals accounted for over 90% of the variance. The spatial distribution of terrestrial water loading displacement is strongly associated with regional precipitation patterns, showing smaller amplitudes in the northeast and northwest and larger amplitudes in the southwest. The research findings presented in this paper offer a novel perspective on the spatiotemporal variations of environmental load effects, particularly those related to the terrestrial water loading deformation with significant spatial heterogeneity. Accurate assessment of the effects of terrestrial water loading displacement (TWLD) is of considerable importance for precise geodetic observations, as well as for the establishment and maintenance of high-precision dynamic reference frames. Furthermore, the development of TWLD model that integrates GRACE and GNSS data provides valuable data support for the higher-precision inversion of changes in terrestrial water storage. [ABSTRACT FROM AUTHOR]