Topological phase boundary in a generalized Kitaev model

We study the effects of the next-nearest-neighbor hopping and nearest-neighbor interactions on topological phases in a one-dimensional generalized Kitaev model. In the noninteracting case, we define a topological number and calculate exactly the phase diagram of the system. With addition of the next-nearest-neighbor hopping, the change of phase boundary between the topological and trivial regions can be described by an effective shift of the chemical potential. In the interacting case, we obtain the entanglement spectrum, the degeneracies of which correspond to the topological edge modes, by using the infinite time-evolving block decimation method. The results show that the interactions change the phase boundary as adding an effective chemical potential which can be explained by the change of the average number of particles.     

Effects of the Bond-Bending Term and e-e Interactions on the 2D Localized Modes Around a Polaron in Trans-Polyacetylene

The 2D localized modes of trans-(CH)_x around a polaron have been studied using a twodimensional extension of the SSH model that includes the bond-bending effect and the electron-electron interactions. The results show that 1) a number of additional localized modes have been found, which depend on the bond-bending term; 2) the number oflocalized modes does not change after turning on the e-e interactions, but their frequencies have been moved and the localization has been strengthened.     

New Energy Spectra Structure of Polaron in Trans-Polyacetylene

In the weakly coupled electron-phonon systems, the existing theory pointed out that the energy spectra of polaron include four electronic bound states. Our work shows that, due to the non-nearest neighbor hopping interactions, the electron-hole symmetry of the energy band structure implied by SSH model is broken, and the numbers of the bound electronic states are changed. For a negative charged polaron, one new bound state is found near the bottom of conduction band, and the original two bound states below the bottom of the valence band and above the top of the conduction band disappear. For a positive charged polaron, five bound states have been found: one of them is an additional bound state at the top of the conduction band, the others are just the states found in the SSH model. Besides, the energy gap 2Δ is slightly shifted by turning on the long-range hopping interactions.     

Lattice vibrational analysis of polyacene

Within an extended Su-Schrieffer-Heeger model, we made a lattice vibrational analysis of polyacene. In a singly-charged polyacene, the ground state contains an interchain-coupled polaron of quasi-D2h symmetry, around which we found thirteen localized modes in total. Among these localized modes, five (three B2u and two B3u) are infrared active, six (four Ag and two B1g) modes are Raman active, and the other two localized modes are asymmetric, which are both infrared active and Raman active. For the case a charged polaron is coupled with a neutral soliton in a finite polyacene chain, the vibrational modes are also calculated to display the coupling effect between self-trapping excitations on phonons. It is found that the localized phonons are determined mainly by the charged polaron, but the number and frequencies of the localized modes are influenced by the existence of the neutral soliton.     

Interaction-induced collapse of a section of the Fermi sea in the zigzag Hubbard ladder

Using the next-nearest-neighbor (zigzag) Hubbard chain as a one-dimensional model, we investigate the influence of interactions on the position of the Fermi wave vectors with the density-matrix renormalization-group technique. For suitable choices of the hopping parameters we observe that electron-electron correlations induce very different renormalizations for the two different Fermi wave vectors, which ultimately lead to a complete destruction of one section of the Fermi sea in a quantum critical point.     

On the possibility of electric transport mediated by long living intrinsic localized solectron modes

We consider a polaron Hamiltonian in which not only the lattice and the electron-lattice interactions, but also the electron hopping term is affected by anharmonicity. We find that the one-electron ground states of this system are localized in a wide range of the parameter space. Furthermore, low energy excited states, generated either by additional momenta in the lattice sites or by appropriate initial electron conditions, lead to states constituted by a localized electron density and an associated lattice distortion, which move together through the system, at subsonic or supersonic velocities. Thus we investigate here the localized states above the ground state which correspond to moving electrons. We show that besides the stationary localized electron states (proper polaron states) there exist moving localized solectron states which can be easily excited. The evolution of these localized states suggests their potential as new carriers for fast electric charge transport.     

Theoretical prediction of intrinsic self-trapping of electrons and holes in monoclinic HfO2

We predict, by means of ab initio calculations, stable electron and hole polaron states in perfect monoclinic HfO2. Hole polarons are localized on oxygen atoms in the two oxygen sublattices. An electron polaron is localized on hafnium atoms. Small barriers for polaron hopping suggest relatively high mobility of trapped charges. The one-electron energy levels in the gap, optical transition energies and ESR g-tensor components are calculated.     

Discrete modulational instability and bright localized spin wave modes in easy-axis weak ferromagnetic spin chains involving the next-nearest-neighbor coupling

We report a theoretical work on the properties of modulational instability and bright type nonlinear localized modes in one-dimensional easy-axis weak ferromagnetic spin lattices involving next-nearest-neighbor couplings.With a linear stability analysis, we calculate the growth rates of the modulational instability, and plot the instability regions.When the strength of the next-nearest-neighbor coupling is large enough, two new asymmetric modulational instability regions appear near the boundary of the first Brillouin zone.Furthermore, analytical forms of the bright nonlinear localized modes are constructed by means of a quasi-discreteness approach.The influence of the next-nearest-neighbor coupling on the Brillouin zone center mode and boundary mode are discussed.In particular, we discover a reversal phenomenon of the propagation direction of the Brillouin zone boundary mode.     

Competition Between the SDW and CDW in Quasi-One-Dimensional Organic Polymer Ferromagnet

The next-nearest-neighbor hopping interactions of ρ-electrons in quasi-onedimensional organic polymer ferromagnet are considered by Peierls-Hubbard model, and a set of self-consistent equations are established to optimize the system. The competition between the SDW and CDW states, which is determined by the interplay between the electron-electron correlation and the next-nearest-neighbor hopping interaction, is studied. At the CDW state,the SDW along the main chain will be tuned by the CDW. Consequently the ferromagnetic state, in which all the spins of the unpaired electrons at side freeradicals are arranged parallelly,will be no longer a stable ground state of the system.     

Polarons in suspended carbon nanotubes

We prove theoretically the possibility of electric-field controlled polaron formation involving flexural (bending) modes in suspended carbon nanotubes. Upon increasing the field, the ground state of the system with a single extra electron undergoes a first-order phase transition between an extended state and a localized polaron state. For a common experimental setup, the threshold electric field is only of the order of approximately equal 5×10(-2) V/μm.     

Spectral Weight Function and Charge-Excitation Gap of the Half-Filled 2D Hubbard Model

Using the combination of the quantum Monte-Carlo and the maximum entropy methods, we study the singleparticle spectral weight function for the half-fiUed two-dimensional Hubbard model including the next-nearest-neighbor hopping. In both the weak- and strong-coupling regimes, it is found that a gap persists as the next-nearest-neighbor hopping is turned on. This indicates that a well-defined chargeexcitation gap is a universal nature of the model, irrespective of its band structure.     

次近邻电子跳跃对孤子的电子束缚态和孤子附近局域模的影响

从SSH模型出发,考虑电子次近邻跳跃的影响,研究了聚乙炔中孤子的电子束缚态和孤子附近的局域振动模。结果发现:1.电子能谱中的电子-空穴对称性消失;2.孤子的电子束缚态的数目和位置发生了变化,且与孤子的类型有关;3.孤子附近出现了一个新的局域振动模G₆;4.次近邻电子跳跃改变了局域模的频率,增强了局域模的局域性。 关键词：     

一维极化子的定域振动模

本文研究了一维电子-晶格耦合系统中极化子的晶格振动,发现了两个新的定域振动模g₆和g′₆,它们分别在一定的耦合参量λ的范围内存在。本文还给出了各个定域振动模的频率和位形随λ的变化情况。 关键词：     

Dynamics of Polaron at Polymer/Polymer Interface

The migration of a polaron at polymer/polymer interface is believed to be of fundamental importance for the transport and light-emitting properties of conjugated polymer-based light emitting diodes. Based on the one- dimensional tight-binding Su-Schrieffer-Heeger （SSH） model, we have investigated polaron dynamics in a one- dimensional polymer/polymer system by using a nonadiabatic evolution method. In particular, we focus on how a polaron migrates through the conjugated polymer/polymer interface in the presence of external electric field. The results show that the migration of polaron at the interface depends sensitively on the hopping integrals, the potential barrier induced by the energy mismatch, and the strength of applied electric field which increases the polaron kinetic energy.     

Effects of next-nearest-neighbor hopping interaction on polaron excitations in pernigraniline-base

The role of next-nearest-neighbor hopping interaction in determining the band structures and lattice configurations of combined polarons in pernigraniline-base polymer is explored on the basis of the Baranowski-Büttner-Voit (BBV) model. Numerical calculations show that the valence band extends to a larger range while the conduction band acts to the contrary, as the strength of the next-nearest-neighbor hopping interaction increases. The width of the Peierls gap and the number of the bound states trapped in have almost no changes. If the coupling strength β<0.15, the transition energy from the lower gap level to the higher one for a combined electron-polaron matches the long-lived 1.5 eV photoinduced absorption peak [J.M. Leng, R.P. McCall, K.R. Cromack, Y. Sun, S.K. Manohar, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. B 48 (1993) 15719], and also supports the high temperature dispersion in the thermally stimulated depolarization current (TSDC) experiment [A.N. Papathanassiou, J. Grammatikakis, S. Sakkopoulos, E. Vitoratos, E. Dalas, J. Phys. Chem. Solids 63 (2002) 1771]. For a combined hole-polaron, new shallow level emerges when β∼0.12.     

Influence of spin–orbit interactions on the polaron properties in wurtzite semiconductor quantum well

We have study the simultaneous effect of Rashba and Dresselhaus spin–orbit interactions on the polaron properties in wurtzite semiconductor quantum wells. The linear and cubic contributions of the bulk Dresselhaus spin–orbit coupling and the effects of phonon confinement on electron–optical-phonon interaction Hamiltonians are taken into account. We have found analytical solutions for the polaron energies as well as polaron effective mass within the range of validity of perturbation theory. It is shown that the polaron energy and effective mass correction are both significantly enhanced by the spin–orbit coupling. Wave number dependent phonon contribution on the electron energy has minima and varies differently of the spin-up and spin-down states. Polaron self-energy due to interface optical phonon modes has larger values than of the confined optical phonon modes ones. The polaron effective mass exhibits anisotropy and the contribution of the Dresselhaus spin–orbit coupling term on the polaron effective mass is dominated by Rashba one.     

Electronic transport mechanisms in tetraphenyleprophyrin thin films

Thermally-evaporated thin films of tetraphenylporphyrin, TPP, with thickness range from (175 to 735) nm had been prepared. Annealing temperatures ranging from (273–473) K do not influence the amorphous structure of these films. The influence of environmental conditions: film thickness, temperature and frequency on the electrical properties of TPP thin films had been reported. It was found that dc conductivity increases with increasing temperature and film thickness. The extrinsic conduction mechanism is operating in temperature range of (293–380) K with activation energy of 0.13 eV. The intrinsic one is in temperatures >380 K via phonon assisted hopping of small polaron with activation energy of 0.855 eV. The ac electrical conductivity and dielectric relaxation in the temperature range (293–473) K and in frequency range (0.1–100) kHz had been also studied. It had been shown that theoretical curves generated from correlated barrier hopping (CBH) model gives the best fitting with experimental results. Analysis of these results proved that conduction occurs at low temperatures (300–370) K by phonon assisted hopping between localized states and it is performed by single polaron hopping process at higher temperatures. The temperature and frequency dependence of both the real and imaginary parts of dielectric constant had been reported.     

Generalized adiabatic polaron hopping: Meyer-Neldel compensation and Poole-Frenkel behavior

The commonly employed adiabatic treatment of polaron hopping is extended to treat the continuous alteration of a carrier wave function with the atoms' movements and a carrier's long-range interaction with a polar surrounding. These features, respectively, introduce carrier-induced softening of the atoms' vibrations and a hopping activation energy that depends on hopping distance. The Meyer-Neldel compensation effect results from carrier-induced softening of vibrations. Poole-Frenkel behavior emerges for electric-field driven polaron hopping in ionic and polar media.     

Muon diffusion in metals

The hopping rate W of the positive muon in metals is studied theoretecally. We consider four interactions: muon-electron interaction, linear as well as quadratic muon-lattice interactions and inhomogeneous broadening of the muon levels due to imperfections. The W-vs-T curve consists of four regions. The highest-T region, where the small polaron theory is applicable, is followed by a minimum, below which the Kagan-Klinger damping may be dominant. Then, the damping due to metallic electrons dominates and the hopping rate obeys a power law of a negative power. When kT is smaller than the inhomogeneous broadening, the hopping rate obeys another power law of a positive power, as Sugimoto has shown. We analyze experimental data on muon diffusion in Cu, Al and Fe.