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The interaction of the doped holes with lattice vibrations in an antiferromagnetic (AF) background is studied using the t − J -Holstein model on an 8-site cluster with 2-holes by an exact method. The phonon mediated interactions between the holes at nearest-neighbor (NN) sites are considered. We have calculated the effective kinetic energy, hole-phonon and hole–hole correlations, two hole binding energy to study the nature and stability of various quasiparticles. At negligible to very weak hole-phonon ( h − p h ) couplings, the holes get dressed by the AF background forming spin-polarons. At weak to intermediate h − p h couplings, the holes are dressed by the phonon cloud forming large hole-polarons and/or nearly free hole-polarons. A narrow transition region is observed at intermediate h − p h coupling depending on phonon energy, which marks the formation of S1 hole-bipolarons and small-hole-polarons. At strong coupling regime, stable hole-bipolarons are formed which may lead to superconducting condensation. We also argue that these results cannot be completely reproduced by considering pure attraction between holes. Results show the relevance of inter-site h − p h coupling in high T c cuprates.

We consider the problem of energy transport in a Davydov model along an anharmonic crystal medium obeying quartic longitudinal interactions corresponding to rigid interacting particles. The Zabusky and Kruskal unidirectional continuum limit of the original discrete equations reduces, in the long wave approximation, to a coupled system between the linear Schrodinger (LS) equation and the modified Korteweg–de Vries (mKdV) equation. Single- and two-hump bright soliton solutions for this LS–mKdV system are predicted to exist by variational means and numerically confirmed. The one-hump bright solitons are found to be the anharmonic supersonic analogue of the Davydov's solitons while the two-hump (in both components) bright solitons are found to be a novel type of soliton consisting of a two-soliton solution of mKdV trapped by the wave function associated to the LS equation. This two-hump soliton solution, as a two component solution, represents a new class of polaron solution to be contrasted with the two-soliton interaction phenomena from soliton theory, as revealed by a variational approach and direct numerical results for the two-soliton solution.

An obvious resistive switching (RS) was observed in BaTiO / 3 FeMn/BaTiO3 (BFB) trilayer films under different conditions. The RS effect was enhanced in light irradiation and restrained in magnetic field. The ratio of high resistance to low resistance of samples annealed at 500 °C is larger than 1500, and the samples showed a good stability. SET and RESET voltages decrease with increasing illumination intensity, but the ON/OFF ratio showed an inverse tendency. Conduction mechanisms in low resistance and high resistance were determined to be Ohmic and space charge limited conduction (SCLC) mechanism, respectively. A redistribution of oxygen vacancies and bound magnetic polaron (BMP) were used for explanation of the mechanism of RS behavior in this system under light irradiation and magnetic field, respectively.

The transport of a dissociated bipolaron in organic one-dimensional lattices is theoretically investigated in the scope of a tight-binding model that includes electron-lattice interactions and an external electric field. Remarkably, the results point to a physical picture in which the dissociated bipolaron propagates as a combined state of two free-like electrons that coherently perform spatial Bloch oscillations (BO) above a critical field strength. It was also obtained that the BO's trajectory presents a net forward motion in the direction of the applied electric field. The impact of dynamical disorder in the formation of electronic BOs is determined.

Based on the one-dimensional extended Su–Schrieffer–Heeger model, we theoretically investigate the effect of interchain coupling on the formation and polarization of the single-excited state of polaron in conjugated polymers. It is found that there exists a turnover value of the coupling strength, over which the excited polaron could not be formed in either of the two coupled chains. Instead, a polaron-like particle is localized at the center of each chain. In addition, we also find that the reverse polarization of the excited polaron could be enhanced for some cases in polymer when the interchain coupling becomes strong until it exceeds the critical value.

This study investigates the structure and conduction mechanism of Sm2NiMnO6 prepared via auto-ignition method. Rietveld refinement of the XRD pattern confirms the monoclinic structure with space group P21/n. This crystal structure is discussed in details. The room temperature conductivity is 1.6 × 10 − 6 Ω − 1 cm − 1 . The values of total activation energy, dc activation energy, hoping energy and migration energy are 0.43 eV, 0.44 eV, 0.43 eV and 0.43 eV respectively. The closed value of all activation energy confirms the conduction of charge carriers via hopping mechanism. Variable range hopping model confirms the small polaron hopping in the material.

In this work, the Pb(Zr0.2Ti0.8)O3/(La0.67Ca0.33)MnO3 heterostructure film is deposited on the Pt/Ti/SiO2/Si wafer. The dominant transport is the inelastic hopping conduction. Due to the interaction between ferroelectric domain and magnetic polaron, film still exhibits weak ferromagnetism above the Curie temperature. Under lower bias voltage, the non-zero sequential magnetoresistance occurs on the magnetic granular junction. As soon as bias voltage exceeds the coercive voltage, the ferroelectric domain is aligned, consequently the magnetoresistance tends to vanish. Such electric switch of magnetoresistance is potential for the electric-write magnetic-read storage device.

We show that the high- T c cuprates are non-BCS superconductors exhibiting distinct pseudogap (PG) behaviors (related to real and momentum space excitations) and other anomalies above T c , novel Bose-liquid superconductivity below T c , and also a λ -like superconducting (SC) transition at T c similar to the λ transition in liquid 4 He. In these materials, the relevant charge carriers are polarons which are bound into bosonic Cooper pairs above T c followed by condensing into a Bose superfluid at T c . We found that the polaronic effects and related PG weaken with increasing of the doping level and disappear in the overdoped region, where the crossover from Bose-liquid to Fermi-liquid (BCS-type) superconductivity occurs at the quantum critical point. We identify the real phase diagrams of the cuprates, the PG and vortex-like states above T c , the novel SC state and two distinct SC phases below T c like two superfluid phases of 3 He, and explain the rich cuprate phenomenology from lightly doped to overdoped region.

Based on non-equilibrium Green's functions' theory and small polaron transformation's technology, we study the heat generation by current through a single-molecular spin-valve. Numerical results indicate that the variation of spin polarization degree can change heat generation effectively, the spin-valve effect happens not only in electrical current but also in heat generation when Coulomb repulsion in quantum dot is smaller than phonon frequency and interestingly, when Coulomb repulsion is larger than phonon frequency, the inverse spin-valve effect appears by sweeping gate voltage and is enlarged with bias increasing. The inverse spin-valve effect will induce the unique heat magnetoresistance effect, which can be modulated from heat-resistance to heat-gain by gate voltage easily.

The investigation of wide range of temperature and frequency dependent conductivity of some semiconducting glassy system reveals DC conductivity, crossover frequency and frequency exponent. The composition dependence of AC conduction activation energy and the permissible energy of polaron migration have also been computed. The Nernst-Einstein relation proves that the concentration of mobile charge carriers does not undertake a substantial part in electrical conduction.

It is demonstrated for the first time that the strong coupling between spin moments of copper ions and oxygen holes, which arises upon hybridization mixing of two hole subsystems in the Emery model, not only affects the formation of spin polaron quasiparticles but also ensures effective attraction between them via the exchange interaction. This results in the Cooper instability with d-wave pairing in a 2D ensemble of spin polaron quasiparticles. The T – x phase diagram obtained using this approach agrees well with the available experimental data.

The magnetotransport properties of Ca0.85Gd0.15MnO3 have been studied analyzing the temperature and magnetic field dependent resistivity. High temperature ( T > T CO : charge ordering temperature) conductivity has been found to be described by the non-adiabatic small polaron hopping (SPH) model. The manganite shows a parallel combination of SPH and variable range hopping (VRH) model below T CO . VRH model fits the corresponding low temperature data. The field depended magnetoresistance (MR) has been investigated with a phenomenological model considering the spin-polarized tunneling. The field dependent MR in scaled coordinate collapses into single curve demonstrating the temperature-independent behavior.

Strong electron–phonon interaction (EPI) generating spontaneous breaking translational symmetry (polarons formation) is acknowledged in lightly doped cuprates due to interpretation of broad bands in their ARPES and optical conductivity spectra. To study systems with strong EPI at significant carrier density we construct distribution suitable for carriers with momentum uncertainty. Obtained concentrations of carriers in different states are used to predict ARPES spectra of such systems. Doping evolution of spectra calculated and “vertical dispersion” in them demonstrate the excellent qualitative and quantitative agreement with those observed in cuprates. “Vertical dispersion” in undoped and essentially doped cuprates is understood from a single viewpoint.

Using non-equilibrium Green's functions' technology combined with small polaron transformation, we theoretically study the inelastic spin Seebeck effects in a controllable Aharonov–Bohm interferometer based on a degenerate molecular quantum dot level. The numerical results show that when the direct coupling between electrodes is switched on, the spin-dependent thermoelectric efficiency will be suppressed, but the magnetic flux can modulate the thermoelectric line-shapes regularly and the pure spin current generation can be achieved by the temperature gradient. When the direct coupling between electrodes is closed, the spin-dependent thermoelectric efficiency will be raised greatly and the heating resulting from the electron–phonon coupling can improve it effectively.

We use the tight-binding Su–Schrieffer–Heeger model for the one-dimensional conjugated polymers to explore the static polarization behavior of a high energy photon-excited state under the electric field. An obvious reverse polarization is obtained although the electric field is weak. With the increase of field strength, the degree of polarization increases first and then decreases. When the electric field is strong enough, the excited state is dissociated into the polaron pair. In addition, the effects of electron–electron interaction and interchain coupling are also discussed. The results indicate that the electron–electron interaction could weaken the reverse polarization of the high energy photon-excited state, which tends to be dissociated into a high-energy exciton and a pair of solitons with the including of interchain coupling.

Li2MnO3 compound is one essential component of the Li-rich solid solution cathode material (mLi2MnO3⋅nLiMO2, M = Mn, Ni, Co, etc.) for lithium ion batteries. The intrinsic insulating nature of the electronic structure determines that the electronic conductivity of the Li2MnO3 compound is low, which is unfavorable to the fast charge/discharge performance of the battery. In this paper, we demonstrate that F doping can create polaron states in the Li2MnO3 lattice from first principles calculations. The small polaron migration energy barrier in the Li2MnO3 lattice is about 0.27 eV. It is also observed that the polaron state is strongly trapped by the F atom, which decreases the efficiency of the doping enhanced electronic conductivity.

The aim of the work is to study the structure of a one-dimensional (1D) bipolaron, taking into account three types of correlation effects: such as interelectronic correlations caused by the direct dependence of the wave function on the distance between electrons as well as the one-center and two-center correlations. Gaussian orbitals with exponentially-correlated multipliers were used for variational calculations. It is shown that in the domain of existence of an 1D optical bipolaron – unlike in a 3D system – a two-center bipolaron is formed. The one-center bipolaron configuration becomes energetically favorable as compared to the two-center one for V C ≤ 1.2 (where V C is interelectronic repulsion parameter). This domain corresponds to an acoustical or acousto-optical bipolaron in the strong-coupling limit.

We report the effects of electron-phonon coupling on the charge density distribution of polarons in armchair nanoribbons of silicene by using an extended tight-binding model with lattice relaxation. The results show that the charge distribution in silicene nanoribbons is analogous to graphene and that the charge localization increases when the intensity of electron-phonon coupling also increases. We further show that silicene nanoribbons may be a conducting or semiconducting material, depending on both the width of the nanoribbon and the possibility of polaron formation. This contribution provides additional insight into the behavior of polarons in silicene nanoribbons, systems of great interest.

Based on the density matrix approach and the perturbation treatment, the polaronic effect on the linear and nonlinear intersubband optical absorption coefficients in quasi-one-dimensional wurtzite nanowires (NWs) is investigated. The simple analytical formulas for polaronic states and the linear and nonlinear optical absorption coefficients in the NW systems are also deduced. Numerical calculation on a freestanding wurtzite GaN NW is performed. The polaronic effect and quantum size effect as well as the influence of incident optical intensity on the optical absorption properties are analyzed and discussed. The results show that, the polaronic effect results in significant increase of the absorption coefficients, and obvious decrease of saturation absorption intensity. In order to observe strong optical absorption, a nitride NW with relative small radius should be chosen. Moreover, a comparison with the situation of GaN-based quantum well systems is also done, and the profound physics is analyzed reasonably.

The control of exciton transport in conjugated polymers is of fundamental importance for luminescence and photovoltaic properties of polymeric optoelectronic devices. We have investigated the elastic scattering processes of a negative polaron and a neutral exciton in a conjugated polymer chain in the presence of an external electric field. We demonstrate that the exciton can be pushed or pulled to transport in a given direction by the polaron, or migrate by exchanging positions with the polaron in particular range of electric field strength. The exciton can preserve quantum coherence in these field induced transfer processes. The manner of exciton motion depends on the spin configuration of the exciton and the polaron as well as the electric field strength. This knowledge will serve to understand the dynamics of intrachain energy transport in conjugated polymers.

A theoretical study is presented on the dynamics of polaritons in semiconductor microcavities near parametric instability thresholds. With upward or downward ramp of optical pump, different instability modes emerge in parameter space defined by damping and detuning. According to these modes, stationary short-wave, stationary periodic, oscillatory periodic, and oscillatory uniform parametric instabilities are distinguished. By multiple scale expansion, the dynamics near threshold can be described by a critical mode with a slowly varying amplitude for the last three instabilities. Furthermore, it is found that the evolutions of their amplitudes are governed by real or complex Ginzburg–Landau equations.

A semi-empirical Peierls–Holstein model is applied to studies of the stability of polarons in two-dimensional molecular crystal systems. Calculations for a broad range of intra- and inter-molecular parameters within this model were performed in order to obtain detailed knowledge concerning the stability of the polaron solution with respect to a rigid lattice band solution. For realistic values of the parameters the polaron solution is stable with a polaron energy in the range 50–100 meV. A metastable polaron solution is also identified. The polarons that result from our model are highly localized and it is questionable if adiabatic polaron transport can occur in the system.

We study the single-polaron properties of the one-dimensional Holstein and SSH model. The dynamical coherent potential approximation (under the Hartree approximation) is applied to compute the polaron dispersion, the quasi-particle residue, and the polaronʼs Greenʼs functions. We compare our calculated results in comparison with those by the self-consistent Born approximation plus higher-order diagrams.

The optical refractive index changes considering polaron effects in asymmetrical quantum wells are theoretically studied. It is shown that a pronounced optical refractive index changes dependence of the quantum well parameters can be obtained. Moreover, the theoretical values of the optical refractive index changes obviously increase when considering the electron–LO–phonon interaction.

A unified physical model for thermopower was presented in organic semiconductors, based on the Marcus theory and variable-range hopping theory. According to the proposed model, the characteristic of charge carrier thermoelectric transport in organic semiconductors has been investigated. In particular, polaron effects, energetic disorder, and carrier density dependence of the thermopower have been discussed in detailed. The calculation also shows a good agreement with the experimental data in organic semiconductors.

We study current and heat of an Aharonov–Bohm ring with a quantum dot, and find that the circulating current can be modulated by the transport current. Similar to the transport current, the circulating current is reduced by the polaron effect. Moreover, there exists an additional contribution from the electron–phonon interaction.

According to recent experimental findings the leading pairing resides in the nodal (FS arcs) momentum region of hole doped cuprates. The pseudogap is an antinodal feature. A corresponding multiband model of the electronic background evolving with doping serves the usually presented phase diagram. The pairing is due by the pair-transfer between overlapping nodal defect (polaron) band and the itinerant band. A bare gap vanishing with extended doping between the antinodal defect subband and the itinerant band top leads to the formation of the pseudogap as a perturbative band-structure effect. The calculated behaviour of two superconducting gaps and of the pseudogap on the whole doping scale is in qualitative agreement with the observations. Arguments to include cuprates into the class of multiband–multigap superconductors are given by these results.

A variational method is used to study the ground state of a bound polaron in a weakly oblate wurtzite GaN/Al x Ga 1 − x N ellipsoidal quantum dot. The binding energy of the bound polaron is calculated by taking the electron couples with both branches of LO-like and TO-like phonons due to the anisotropic effect into account. The interaction between impurity and phonons has also been considered to obtain the binding energy of a bound polaron. The results show that the binding energy of bound polaron reaches a peak value as the quantum dot radius increases and then diminishes for the finite potential well. We found that the binding energy of bound polaron is reduced by the phonons effect on the impurity states, the contribution of LO-like phonon to the binding energy is dominant, the anisotropic angle and ellipticity influence on the binding energy are small.

Migration of small polarons in λ-MnO2, Li0.5Mn2O4 and LiMn2O4 is studied via first principles calculations. Migration energy barriers of single small polaron migrations in λ-MnO2, Li0.5Mn2O4 and LiMn2O4 are 0.22 eV, 0.45 eV and 0.35 eV, respectively. The energy level changes of Mn-3d states along the polaron migration path are analyzed in detail. Results indicate that the activation energy barrier of polaron migration is strongly associated with the energy level shift of Mn- 3 d z 2 orbital, which is dependent on the short range structural arrangement of Mn3+/Mn4+ in the crystal. The electrical conduction properties of LixMn2O4 at room temperature are then discussed.

We investigate the effect of temperature on polaron dynamics in the framework of a tight-binding model. The dissociation of a polaron will become fast with the increase of temperature. There exists a crossover of the charge localization time from strong to weak temperature-dependence. Instead of the uniform motion at zero temperature, a polaron moves un-uniformly under a driven field at a finite temperature, which indicates a discrete hopping between base pairs. It is also found that the polaron motion is thermally activated. A high temperature will result in a fast movement of a polaron under a deriving field.

Antiferroelectric spin wave resonance (AFESWR) and electric spin moment, mathematically predicted by Dirac, were identified for the first time. It has also been found, in addition to well-known SSH-model, that topological quasiparticles, called σ -quasiparticles, can be formed in C C σ -bonds of organic polymers. Topological σ -polaron lattice is proposed to be responsible for the observed AFESWR both in starting polyvinylidene fluoride (PVDF) films and in carbynoid films, which are the products of PVDF-dehydrohalogenation. Dynamical systems of σ -polarons and π -solitons, identified in the samples studied, are substantionally nonlinear and can be registered in stochastic regime by usual IR absorption measurements.

We investigate the effect of helix angles on polaron motion in poly-DNA in the framework of a tight binding model. A DNA molecule is supposed to have a uniform or a random distribution of the helix angles. It is found that a polaron moves faster along a DNA molecule with an overwinding helix than that with an unwinding one. In DNA molecule with randomly distributed helix angles, charge transport is suggested to be field-facilitated tunneling between spatial disordered potential wells.

We propose to achieve spin injection in an organic device by a spin polarized self-assembled monolayer (SPSAM), which is used to tune the spin-dependent coupling between electrode and organic polymer. The results show that spin injection can be realized by both the spin selection and spin manipulation effects of the SPSAM. Interestingly, we found spin polarized wave-packet as a consequence of the spin injection, which is a mix of a normal spin polaron and a spinless bipolaron.

A Green function formalism is applied to study the dielectric function spectra and the small polaron hopping conduction in organic molecular crystals. In the calculations, the electron–phonon interaction is considered within the Hartree–Fock approximation, and the temperature effect is taken into account. Our theoretical approach is based on the polar electron–phonon interaction (Frohlich type) to characterize the non-degenerate polaron gas, with the assumption of the electronic hopping between the first-neighbor.

Polarons and bipolarons are main carriers in conducting polymers. It is shown that a bipolaron can open a channel of electroluminescence, which does not involve a triplet exciton, and can enhance the efficiency of electroluminescence. The dynamics of this channel is simulated.

Relaxation process of self-trapped polaron is investigated by a nonadiabatic molecular dynamic method. We show localized disorder due to lattice fluctuations can give rise to a tightly-bound electronic state in ultraviolet illuminated SrTiO 3 crystal. This bound state is actually a self-trapped polaron in accordance with the experimentally observed large Stokes-shift. The formation of the self-trapped polaron is shown to be an ultrafast process.

A Green function formalism is employed to perform an analytical calculation of the dielectric function due to an electron–phonon interaction within a Hartree–Fock approximation. Our theoretical approach is based on the polar or Frohlich type of electron–phonon interaction, with the electronic hopping between the first-neighbor, to characterize the polaron model. Our numerical results for the dielectric function profile show resonant peaks, all of them at lower frequencies than the main one, attributed to the polaron crossover regime between the quasi-free-electrons and the small polarons.