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Since controlling strain in different types of heterostructures devices causes the improvement of properties and functionalities in real devices, considering this matter is vital in simulation. In this paper, the impact of strain in the interface of different layers of solar cells has been investigated with density functional theory (DFT) and finite-difference time-domain (FDTD) techniques. We have simulated the complex issue of strain and relaxation of atomic layers by using a new, effective and simple method and using a precise meshing technique. The amplitude and region of the strain have been meshed to specific values. The lattice strain is included in both simple and gradient patterns in the theoretical simulations. The strain factor has been considered in two steps; between active layers in solar cells and between the active layer and the electron transport layer (ETL). DFT results indicate alterations in the structural and optical properties of the material as a function of strain. The results of DFT have been used in FDTD simulation. To describe this new method, we used perovskite as the active layer in the solar cell. We realized that the electric and optical parameters such as short circuit current density, absorptance, and reflectance of strained solar cells are different in comparison to strain free cells, and applying strain to the contacting layers in the solar cell alters the optoelectronic properties of the device.

We have designed high-efficient spin-filtering junctions composed of graphene and silicon carbide nanoribbons. We have calculated the spin and charge transport in the junction by non-equilibrium Green’s function formalism combined with the density functional theory to find its spin-dependent electrical conductance, thermal conductance and Seebeck coefficient. In addition, the effect of Si and C atoms vacancies on the transport properties of the junction has been carefully investigated. The enhanced spin-filtering is clearly observed due to the edge and vacancy effects. On the other hand, vacancy defects increase the electrical and spin conductances of the junctions. The results show that the considered junctions are half-metal with reduced thermal conductance which makes them a suitable spin-dependent thermoelectric device. Our results predict the promising potential of the considered junctions for application in spintronic devices.

We study the thermoelectric properties of a system that consists of fullerene molecule which connects to graphene nanoribbons . Our research includes C 20 as the smallest fullerenes and C60 as the most stable and abundant type of fullerenes. The calculations are done using the density functional theory and non-equilibrium Green function in a linear response regime. We address properly the important thermoelectric quantities and their behaviors. Results show that doping of fullerene with a nitrogen causes new levels of energy in vicinity of Fermi level. Although doping has different effects on the electrical conductivity , phonon and electron contributions to the thermal conductivity and thermopower of the molecule but it eventually causes the figure of merit increases.

We apply the NEGF + DFT technique to study the effect of anchoring groups on the electronic transport properties of a single pyrene molecule attached to two Au electrodes via three different anchoring groups (namely NO2, NH2 and CN). More specifically, we investigate the effect of asymmetric electrode coupling together with B and N doping on rectification ratio of a pyrene-based molecular device. The results indicate that the rectification ratio can be tuned by selecting configurations of maximum difference in the coupling parameters in the two sides of the gold electrodes, and its magnitude depends on the strength of the electronic coupling of the pyrene molecule to the gold electrodes. In addition, we observe that doping the molecule with B and N atoms decreases the coupling parameters by creating a resonant peak close to the Fermi level.

By using density functional theory calculations, we have studied the effects of V-, Cr-, Mn-, Fe- and Co-doped on the electronic and magnetic properties of the 1T-NiS2 monolayer. The results show that pure 1T-NiS2 monolayer is a non-magnetic semiconductor. Whereas depending on the species of transition metal atom, the substituted 1T-NiS2 monolayer can become a magnetic semiconductor (Mn-doped), half-metal (V- and Fe-doped) and magnetic (Cr-doped) or non-magnetic (Co-doped) metal. The results indicate that the magnetism can be controlled by the doping of 3d transition metal atoms on the monolayer. In this paper, the engineering of the electric and magnetic properties of 1T-NiS2 monolayer is revealed. It is clear that it could have a promising application in new nanoelectronic and spintronic devices.

By using density functional theory calculations, we have studied the effects of V-, Cr-, Mn-, Fe- and Co-doped on the electronic and magnetic properties of the 1T-NiS2 monolayer. The results show that pure 1T-NiS2 monolayer is a non-magnetic semiconductor. Whereas depending on the species of transition metal atom, the substituted 1T-NiS2 monolayer can become a magnetic semiconductor (Mn-doped), half-metal (V- and Fe-doped) and magnetic (Cr-doped) or non-magnetic (Co-doped) metal. The results indicate that the magnetism can be controlled by the doping of 3d transition metal atoms on the monolayer. In this paper, the engineering of the electric and magnetic properties of 1T-NiS2 monolayer is revealed. It is clear that it could have a promising application in new nanoelectronic and spintronic devices.

Based on density functional theory and non-equilibrium Green’s function formalism, we explore the effect of Fe atom in Au-Fe@C20-Au monomer and dimer systems in comparison with the C20 fullerene molecular junctions. We calculate the spin-dependent transmission coefficient, spin polarization and also their spin thermoelectric coefficients to investigate magnetic properties in the system. Our results indicate that the presence of Fe atoms enhances substantially the spin-filter and increases the spin figure of merit in the dimer system. We suggest that the Au-(Fe@C20)2-Au system is a suitable junction for designing spin-filtering and spin thermoelectric devices and eventually it is a good candidate for spintronic applications.

The thermoelectric properties of a Phenanthrene molecule, such as thermopower, electrical conductivity, thermal conductivity and figure of merit, are investigated by applying the non-equilibrium Green's function (NEGF) method combined with the density functional theory (DFT). Phenanthrene is intended to couple to the graphene nanoribbons electrodes in two configurations. The vertical and horizontal orientations of the molecule between the nanoribbons are considered. The results reveal that the thermoelectric properties of the considered structures are dependent on the orientation of Phenanthrene configuration between the electrodes. At high chemical potential, the greatest figure of merit is observed for Phenanthrene, which is vertically attached to the electrodes, because of the small thermal conductivity of this configuration. On the other hand, the symmetric and horizontal configurations of the molecule make it a high-performance thermoelectric device at zero chemical potential.

Bilayer germanene nanoribbons are investigated in different stacks like buckled and flat armchair and buckled zigzag germanene nanoribbons by performing theoretical calculations using the nonequilibrium Greens function method combined with density functional theory. In these bilayer types, the current oscillates with change of interlayer distances or intra-layer overlaps and is dependent on the type of the bilayer. Band gap of AA-stacked of shifted flat bilayer armchair germanene nanoribbon oscillates by change of interlayer distance which is in contrast to buckled bilayer armchair germanene nanoribbon. So, results show the buckling makes system tend to be a semiconductor with wide band gap. Therefore, AA-stacked of shifted flat bilayer armchair germanene nanoribbon has properties between zigzag and armchair edges, the higher current under bias voltages similar to zigzag edge and also oscillations in current like buckled armchair edges. Also, it is found that HOMO-LUMO band gap strongly affects oscillation in currents and their I–V characteristic. This kind of junction improves the switching properties at low voltages around the band gap.

We have discussed effect of electron spin relaxation on optical bistability behavior and lasing without inversion in a three level V-type quantum system. A reasonable range for electron spin relaxation value is chosen to investigate the phenomena previously mentioned. It has been showed that for different values of electron spin relaxation of the system, the bistable threshold intensity and width of hysteresis loop changes dramatically. Following we showed that how one can manipulate the absorption of probe field by variation of electron spin relaxation and achieve laser without inversion in the absence of incoherent field.

In this paper we investigate the optical properties of an open four-level tripod atomic system driven by an elliptically polarized probe field in the presence of the external magnetic field and compare its properties with the corresponding closed system. Our result reveals that absorption, dispersion and group velocity of probe field can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field, magnetic field and cavity parameters i.e. the atomic exit rate from cavity and atomic injection rates. We show that the system can exhibit multiple electromagnetically induced transparency windows in the presence of the external magnetic field. The numerical result shows that the probe field in the open system can be amplified by appropriate choice of cavity parameters, while in the closed system with introduce appropriate phase difference between fields the probe field can be enhanced. Also it is shown that the group velocity of light pulse can be controlled by external magnetic field, relative phase of applied fields and cavity parameters. By changing the parameters the group velocity of light pulse changes from subluminal to superluminal light propagation and vice versa.

In this paper, the effect of plasmonic nanostructure on behavior of optical bistability and multistability in a four-level quantum system embedded in a unidirectional ring cavity has been studied. It is found that the distance between plasmonic nanostructures and a four-level quantum system is varied from 4.4 nm to 14.4 nm and has an essential role for controlling the threshold of optical bistability and multistability. Moreover, obtained results show that the group velocity of pulse propagation through the medium is strongly depended on the distance between the plasmonic nanostructure and the four-level quantum system.

We studied the steady state and transient evolution of probe absorption and population in an open four level N-type atomic system and compared its transient and steady state properties with the corresponding closed system. The effects of incoherent pump field, spontaneously generated coherence, probe detuning and cavity parameters (i.e. the atomic exit rate from cavity and atomic injection rates) on transient and steady state response of probe field and lasing with and without inversion are investigated. It is realized that in an open N-type system, regardless of incoherent pump field applied or not, due to existence of cavity parameter, by adjusting the values of other parameters, we can always obtain lasing without inversion, while there is no gain in closed system without incoherent pump field. Also results are shown that, the probe gain can be greatly amplified with SGC at the presence of incoherent pump field and absence of population inversion. We found that in the same condition the open system is favorable scheme for lasing without inversion.

Using the non-equilibrium Green's function formalism and density functional theory, we have performed a theoretical investigation of the electronic transport properties of borophene/B12N12 cage/borophene system in two armchair configurations (A1 and A2) and one zigzag configuration (A3). In fact, the successful preparation of borophene sheets and also its high electrical conductivity prompted our team to investigate the properties of this structure as electrodes in junction with B12N12 cage. The results show that the considered configurations have distinctly different transport behaviors under bias voltages. Also, the I-V curve follow the pattern A 2 > A 3 > A 1 . These results show that the borophene/B12N12 cage/borophene system at A2 configuration is a suitable candidate for electronics applications.

Inspired by recent success in experimental synthesis of π -conjugated transition metal.bis.dithiolene (TM.b.DT) wires, their charge- and spin-dependent thermoelectric properties have been investigated using density functional theory (DFT) and nonequilibrium Green's function formalism (NEGF). Mn, Co and Ni are considered as TMs in this study. The metal Ni.b.DT wire has the highest electrical conductance versus chemical potential because of having both α and β spin contribution to the transport. Whereas, because of their perfect spin-filtering efficiency at the Fermi level, the Co and Mn half-metal wires have high spin conductance and spin thermopower. In addition, the final results of charge- and spin-dependent thermoelectric efficiency suggests Co.b.DT and Mn.b.DT wires for promising devices in spin-filtering, charge- and spin-thermoelectric sciences.

We have studied the hydrogenation of germanene synthesized on Ge2Pt crystals using scanning tunneling microscopy and spectroscopy. The germanene honeycomb lattice is buckled and consists of two hexagonal sub-lattices that are slightly displaced with respect to each other. The hydrogen atoms adsorb exclusively on the Ge atoms of the upward buckled hexagonal sub-lattice. At a hydrogen exposure of about 100 L, the (1 × 1) buckled honeycomb structure of germanene converts to a (2 × 2) structure. Scanning tunneling spectra recorded on this (2 × 2) structure reveal the opening of a bandgap of about 0.2 eV. A fully (half) hydrogenated germanene surface is obtained after an exposure of about 9000 L hydrogen. The hydrogenated germanene, also referred to as germanane, has a sizeable bandgap of about 0.5 eV and is slightly n-type. © 2018 Author(s).

We have investigated the optical bistability and optical multistability behaviors in a unidirectional ring cavity filled with diamond nitrogen-vacancy (defect centers driven by an elliptically polarized probe field in the presence of magnetic field and compare its properties with the corresponding closed system. Our numerical result demonstrates that threshold of optical bistability and the width of hysteresis loop can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field and cavity parameters, i.e., the electronic exit rate from cavity and electron injection rates. It is also shown that optical bistability and optical multistability are very sensitive to the relative phase between applied fields and magnetic field. It can be realized that by tuning the parameters the transition from bistability to multistability or vice versa can be obtained.

The behavior of the Goos–Hanchen (GH) shifts of the reflected and transmitted probe and signal pulses through a cavity containing four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al 0.3 Ga 0.7 As barriers is theoretically discussed. The biexciton coherence set up by two coupling fields can induce the destructive interference to control the absorption and gain properties of probe field under appropriate conditions. It is realized that for the specific values of the intensities and the relative phase of applied fields, the simultaneous negative or positive GH shift in the transmitted and reflected light beam can be obtained via amplification in a probe light. It is found that by adjusting the controllable parameters, the GH shifts can be switched between the large positive and negative values in the medium. Moreover, the effect of exciton spin relaxation on the GH shift has also been discussed. We find that the exciton spin relaxation can manipulate the behavior of GH shift in the reflected and transmitted probe beam through the cavity. We show that by controlling the incident angles of probe beam and under certain conditions, the GH shifts in the reflected and transmitted probe beams can become either negative or positive corresponding to the superluminal or subluminal light propagation. Our proposed model may supply a new prospect in technological applications for the light amplification in optical sensors working on quantum coherence impacts in solid-state systems.

We investigated the propagation effect on gain without inversion (GWI) phenomena in an open four level quantum dot nanostructure in the presence and absence of incoherent pumping field. The simulation results show that, the ratio of the injection rates and strength of incoherent pumping field has remarkable effect on spatial evolution of GWI and output. We can obtain the optimal GWI and output by choosing appropriate values of parameters. The theoretical results show that, in the open system the value of gain (output) in the absence of incoherent pumping field is much larger than that in the presence of incoherent pumping field.

The thermoelectric properties of a benzene molecule coupled to three-dimensional metallic electrodes are examined in the presence of dephasing processes using Green function formalism in the linear response regime. The three different kind of configurations (ortho, meta and para) are taken into account for the coupling between the molecule and electrodes. Results show that the thermoelectric properties of the single molecular junction are strongly dependent on the coupling geometry. Our results predict that the thermoelectric efficiency is increased in specific geometry as a consequence of interference effects. It is found that the dephasing effects result in the reduction of the thermoelectric efficiency.

The inelastic electron transport properties through two polymeric (trans-polyacetylene and polythiophene) molecular junctions are studied using Keldysh nonequilibrium Green function formalism. The Hamiltonian of the polymers is described via Su–Schrieffer–Heeger model and the metallic electrodes are modeled by the wide-band approximation. Results show that the step-like behavior of the current–voltage characteristics is deformed in presence of strong electron–phonon interaction. Also, the magnitude of current is slightly decreased in the phonon assistant electron transport regime. In addition, it is observed that the I–V curves are independent of temperature.

In this paper, the spectral behavior of two-cell phase conjugating mirror (PCM) with a two-pass Nd:YAG amplifier has been analyzed experimentally and theoretically. For this purpose, input intensity with single and multi-longitudinal modes has been investigated. The numerical model is based on focused geometry model (1+1 dimension) equations of Stokes back-scattered intensity and acoustic waves, for two-cell generator-amplifier phase conjugating mirror with proper boundary conditions that are solved simultaneously with the rate equations of Nd:YAG optical amplifier. Results of the Fourier analysis of the amplified intensity show considerable differences between Fourier amplitudes of the amplifier equipped with PCM and a two-pass amplifier with a conventional mirror under the same output energy. The amplifier with PCM has a completely filtered and different spectral behavior with clearly reduction of the beating between Fourier components of input optical field. Calculations show that the filtering of Fourier components by a PCM is done more effectively with lower pumping energy.

In this paper, we theoretically investigate transmission and reflection properties of incident light through dielectric medium doped by GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al 0.3 Ga 0.7 As barriers, grown by metal organic chemical vapor deposition. The destructive quantum interference is set up by a control pulse that couples to a resonance of biexcitons. We found that many-particle interactions such as biexciton binding energy and biexciton decoherence which are inherent in semiconductors can affect the transmission and reflection properties of incident light on the slab. We have also shown that simultaneous subluminal or superluminal transmission, reflection can be achievable at different frequencies of probe field.

The behavior of the Goos—Hanchen (GH) shifts of the reflected and transmitted probe light beams is theoretically investigated. In a fixed geometrical configuration, the effect of quantum interference induced by spontaneous emission on the phase control of the GH shifts is analyzed in this paper. It is found that in a four-level N-type atomic system as an intracavity medium, the GH shifts of the reflected and transmitted probe light beam are completely phase dependent.

The effect of permanent dipole moments on the optical bistability of weak probe light in a unidirectional ring cavity with a three-level molecule is investigated. It is found that the intensity threshold of optical bistability and optical multistability can be controlled by quantum coherence induced by permanent dipole moments. It is shown that switching from optical bistability to optical multistability and lasing without population inversion can be occurred by this coherence under different conditions.

In this paper, two atomic models are proposed in an 35 nm Er3+-doped YAG crystal. The effect of Er3+ ion concentration and incoherent pumping field on optical bistability is discussed. The results for two models show that the threshold of optical bistability for some Er3+ concentration reduces and for some concentration increases. We display that the incoherent pumping field makes the behavior of optical bistability for two proposed model completely different at identical conditions for Er3+ concentration. Our results show that in the absence and presence of incoherent pumping field some Er3+ concentration can lead to maximum and minimum OB threshold. We hope that our proposed model can be suitable for optimizing and controlling the optical bistability in Er3+:YAG crystal.

Since perovskite solar cells have attracted a lot of attentions over the past years, the enhancement of their optical absorption and current density are among the basic coming challenges. For this reason, first, we have studied structural and optical properties of organic-inorganic hybrid halide perovskite CH3NH3PbI3 and the compounds doped by chlorine halogen CH3NH3PbI3-xClx in the cubic phase by using density functional theory (DFT). Then, we investigate the light absorption efficiency and optical current density of the single-junction perovskite solar cell CH3NH3PbI3-xClx for the values (x=0,1,2,3) by utilizing optical constants (n,k) resulted from these calculations. The results suggest that increasing the amount of chlorine in the CH3NH3PbI3-xClx compound leads an increase in bandgap energy, as well as a decrease in lattice constants and optical properties like refractive index and extinction coefficient of the structure. Also, the results obtained by simulation express that by taking advantage of light trapping techniques of SiO2, a remarkable increase of light absorption will be achieved to the magnitude of 83.13%, which is noticeable., 13 pages, 8 figures

In this paper, we have studied a two pass amplifier with a single and two-cell stimulated Brillouin scattering (SBS) phase conjugating mirrors. The role of longitudinal mode structure on the energy reflectivity of the SBS process and temporal behavior of the reflected pulse has been investigated experimentally. The results for different mode structures including single, double and multi-mode pump pulse for SBS mirrors with single and two cells are compared to each other. Our results show that the two cell SBS mirror has some new advantages over the single cell configuration when the laser oscillator operates in multi-mode regime. We found higher reflectivity at high entrance energy for backwardly amplified Stokes pulse. The mode beating become considerably smaller and fluctuations of Stokes pulse are smoothed in the SBS amplifier.

In this paper, phase control of Kerr nonlinearity in a GsAs multiple quantum wells (MQWs) with 17.5 nm GaAs wells and 15 nm Al0.3Ga0.7 barriers is studied. The role of exciton spin relaxation and biexciton binding energy as well as Rabi frequencies of applied fields on phase control of Kerr nonlinearity and nonlinear absorption is also discussed. It is found that exciton spin relaxation (spin decoherence) and biexciton binding energy which resulted from many-particle interaction in semiconductors have essential roles in producing giant Kerr nonlinearity with nonlinear amplification for some values of relative phase between applied fields. Our study provides a suitable treatment for the next generation of all-optical systems in semiconductor nanostructures. Moreover, we hope that our theoretical work may be helpful for the future experimental works based on many-particle interaction in the semiconductors.

The effect of Er3+ doped ion concentration on optical properties of two type three-level schemes in 35 nm Er3+:YAG (yttrium aluminum garnet) crystal is studied. It is found that intensity threshold of optical bistability and multistability can be changed by Er3+ doped ion concentration. Moreover, switching from optical multistability to optical bistability can be done differently by Er3+ concentration in two types of three-level schemes. The steady-state and transient behaviors of absorption, dispersion and group index of weak probe field in two schemes are also discussed. In this study, we will report an initial study on optical properties in Er3+:YAG crystal and propose a basis for selecting the suitable concentration to carry out experimental investigations in the future.

In this paper, the effect of terahertz signal field on optical bistability and multistability in InGaN/GaN quantum dot nanostructure inside a unidirectional ring cavity is investigated. Quantum dot nanostructure is designed numerically by Schrodinger and Poisson equations which solve self consistently. By size control of quantum dot and external voltage, one can design a four level quantum dot with appropriate energy levels which can be suitable for controlling the optical bistability and multistability by terahertz signal field. It is found that the frequency detuning and intensity control of terahertz signal radiation as well as the dephasing decay rates can influence the optical bistability and multistability behaviors.

In this paper, phase control of optical bistability and multistability based biexciton coherence is investigated in GaAs/AlxGal−xAs semiconductor structure with 15 periods of 17.5 nm GaAs layer and 25-nm Al0.3Ga0.7 barriers, grown by molecular beam epitaxy, four-level quantum dot nanostructure. By two control fields that couple to a biexciton state, the destructive interference can be obtained. In this case, the optical bistability (OB) and optical multistability (OM) can be dramatically altered with adjusting the absorption of two weak probe and signal fields. The results show that the OB and OM behavior of the medium are different for two-weak-pulsed probe fields due to effect of exciton spin relaxation, intensity of coupling fields and relative phase between applied fields.

In this paper, the effect of microwave field on the transient and steady state response of the four-level inverted Y-type atomic system is investigated. It is found that the properties of transient and steady processes can be affected by microwave field. It is found that the absorption spectrum behaves differentially for single-photon absorption and two-photon absorption. Also it is observed that in the one-photon absorption, the microwave field can lead to the probe gain and for two-photon absorption case, the strong microwave can enhance the absorption.

Propagation of Gaussian pulse in a defect dielectric medium in the presence of spin coherence is theoretically investigated. We consider a dielectric slab doped with semiconductor quantum well nanostructure. We show that the reflected and transmitted pulses can be tuned from subluminal to superluminal by changing spin coherence in a slab. Our result predicts that the group velocity of the reflected and transmitted pulses in different wavelengths depend on the thickness of the slab, intensity of the coupling field and relative phase between applied fields.

In this paper, we report theoretical investigation of controlling the optical bistability (OB) and optical multistability (OM) in a GaAs quantum well inside a unidirectional ring cavity. In this scheme quantum interference is raised by a control pulse that couples to a resonance of a biexcitons. It is shown that many-particle interactions which are natural in semiconductors can be used to creation of quantum coherence. In this case optical bistability and multistability can be controlled by biexciton energy renormalization which resulted from many-particle coulomb interactions.

In this paper, group velocity control of Gaussian beam in a dielectric medium doped with nanodiamond nitrogen vacancy (NV) centers under optical excitation is discussed. The shape of transmitted and reflected pulses from dielectric can be tuned by changing the intensity of magnetic field and polarization of the control beam. The effect of intensity of control beam on group velocity is also investigated.

Thermoelectric properties of metal/molecule/metal junction is investigated for different lengths of polythiophene connected to three dimensional metallic electrodes, using Green function formalism in linear response regime. An extended Su–Schrieffer–Heeger model is used to describe the Hamiltonian of polythiophene molecule and a tight-binding model is chosen to study the effect of length change on thermoelectric coefficients of the molecular junction. Increasing the molecular length results in decrease of HOMO–LUMO gap, decrease of the electrical conductance and increase of the value and oscillation of the thermopower. In addition, our results show that the temperature dependence of the thermoelectric coefficients is strongly related to the molecule length.

In this paper, we investigate the effect of incoherent pumping field and exciton spin relaxation on optical properties of four-level biexciton–exciton double cascade-type configuration. It is shown that probe absorption, dispersion and group velocity can be controlled via incoherent pumping field and exciton spin relaxation. Also it is found that the probe absorption is converted to the probe gain in the presence of population inversion.

A novel four-level atomic system which interacted by an elliptically polarized probe field and a control laser field in the presence of external magnetic field is proposed. Here, we are interested in the transient properties of a weak probe field due to its potential application on quantum computing and quantum communication. It is shown that the external magnetic field and relative phase between two electric field components of the probe field can influence the probe absorption and dispersion.

The influence of spin-dependent transport on the thermoelectric properties of a carbon nanotube quantum dot coupled to ferromagnetic leads is investigated using Green function formalism in the linear response regime. The interactions of electron–electron, electron–phonon, and spin–orbit are taken into account. Spin degeneracy is eliminated by applying a magnetic field on the system. The spin conductance and the spin Seebeck coefficient are increased by the increase of magnetic field and polarization of leads, resulting in enhancement of spin figure of merit.

Thermoelectric properties of a carbon nanotube quantum dot such as electrical conductance, thermal conductance, thermopower, and figure of merit are analyzed. Influence of electron–electron, spin–orbit, and electron–phonon (EPI) interactions on the thermoelectric properties of system is taken into account using the Green function formalism in the linear response regime. It is observed that the temperature difference between electron and phonon subsystems results in the fluctuation of the thermopower and enhancement of the figure of merit. It is also found that the figure of merit is reduced in high temperatures due to the bipolar effect induced by the EPI resulting in the reduction of electrical conductance and increase of thermal conductance.

We consider a single level quantum dot interacting with a phonon mode and weakly coupled to metallic leads which are subjected to a time-dependent gate voltage. Electrical conductance, thermopower, and figure of merit are investigated in detail using a Tien–Gordon-type rate equation. In the presence of the microwave field, the electrical conductance exhibits extra peaks whose height is controlled by the magnitude of the microwave field. Furthermore, the oscillation of the thermopower increases in the presence of the time-dependent gate voltage or the electron–phonon interaction. Influence of the electron–phonon interaction, microwave field, temperature, and Coulomb interaction on the figure of merit is also studied.

We analyze spin-dependent transport through a spin-diode in the presence of spin-flip and under influence of temperature bias. The current polarization and the spin accumulation are investigated in detail by means of reduced density matrix. Results show that the spin accumulation is linearly increased when the metallic electrode is warmer whereas, its behavior is more complicated when the ferromagnetic lead is warmer. Spin-flip causes that the current polarization becomes not only a function of spin-flip rate but also a function of temperature. The current polarization is reduced up to 90% if the time of spin-flip is equal to the tunneling time. The behavior of spin-dependent current is also studied as a function of temperature, spin-flip rate, and polarization.

The time-dependent thermopower is analyzed through an interacting quantum dot coupled to a time-dependent gate voltage and under the influence of an external magnetic field using the Keldysh nonequilibrium Green's function formalism. Formal expressions of the electrical and thermal conductances, thermopower, and thermoelectrical figure of merit are obtained. The influence of the magnetic field on the displacement current and the heat current is studied. Results show that although applying time-dependent gate voltage results in the enhancement of the Seebeck coefficient, the electron-electron interaction gives rise to a significant reduction in the thermopower. The reason for why applying time dependent gate voltage results in the enhancement of the thermopower is also analyzed., 10 pages, 4 figures

The electrical conductance, the thermal conductance, the thermopower and the thermoelectrical figure of merit are analyzed through a double quantum dot system weakly coupled to metal electrodes, by means of density matrix approach. The effects of interdot tunneling, intra- and interdot Coulomb repulsions on the figure of merit are examined. Results show that increase of interdot tunneling gives rise to a reduction in figure of merit. On the other hand, increase of Coulomb repulsion results in enhancement of figure of merit because of reduce of bipolar effect.