混合卤化物中的极化子与双极化子

应用紧束缚双带模型对混合卤化物的电荷掺杂性质进行了计算,发现单电荷掺杂在混合卤化物中形成极化子,双电荷掺杂则形成稳定的双极化子;单体的长度和界面耦合都对极化子和双极化子的产生和稳定性有影响.混合卤化物的单体对掺杂电荷具有选择性;电子-电子相互作用并不能使形成双极化子的两个同号电荷相互排斥而形成两个单极化子.在具有电荷自发转移的材料中,混合卤化物单体对掺杂电荷没有像其他混合卤化物一样的选择性,掺杂电荷的定域位置取决于两种单体对该电荷的束缚能力. 关键词： 混合卤化物 极化子 电荷约束     

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.     

长程电子关联对聚噻吩中极化子的影响

采用扩展的SSH模型,加上电子相互作用和长程电子关联,用自洽迭代的方法研究了聚噻吩链中的极化子问题,计算了电子相互作用和长程电子关联对极化子位形和电荷密度的影响,获得了长程电子关联使极化子位形变小,极化子区域变窄,电荷密度震荡减弱,对聚合物中电子的输运的影响不能忽略的有益结果.     

电子关联和孤子

聚乙炔中的电子关联和孤子可用相关基函数方法(CBF)来研究,通过考虑完全的电子-电子相互作用,得到含有单个电荷的奇数原子链的稳定位形为孤子的结论,随着电子-电子互作用强度U和互作用程α/β的增加,孤子定域性加强,产生能降低,因此,即使计入电子-电子相互作用,孤子仍然是导电聚合物中的主要载流子。 关键词：     

非闭环结构下有机磁性材料中的自旋密度波性质

研究了有机磁性聚合物ploy-BIPO链的封闭和非封闭结构对体系自旋密度（SDW)的影响.在开链情况下,自旋耦合与电子-电子相互作用对主链SDW的形成存在竞争,自旋耦合有利于SDW的形成;而电子-电子相互作用对SDW起到抑制作用.闭环下,没有得到这些结论. 关键词：     

Optical properties of charge transfer salts of tetracyanoquinodimethane (TCNQ)

A unified interpretation is given for the infrared and optical spectra of many TCNQ compounds which exhibit a wide variety of physical properties. Inter- and intra-molecular transitions are distinguished by polarization measurements on single crystals of several TCNQ salts. It is suggested that there is incomplete charge transfer in both tetrathiofulvalinium (TTG)- and N-methylphenazinium (NMP)-TCNQ and that the electron-electron interactions are not appreciably screened by the excitonic polarizability of the cations.     

Barrier penetration effects for electrons in quantum wells: screening,mobility, and shallow impurity states

A two-dimensional electron gas in a quantum well confined by finite barriers is considered. We present analytical expressions for the finite confinement effects of a square-well potential and calculate the electron-electron interaction potential, the electron-impurity interaction potential, the interface-roughness scattering potential and the alloy-disorder scattering potential. The dielectric function of the interacting electron gas, the mobility (for charged-impurity scattering, for interface-roughness scattering, and for alloy-disorder scattering), and the binding energy of hydrogenic impurities (screened and unscreened) are discussed.     

Density-matrix renormalization group study of pairing when electron-electron and electron-phonon interactions coexist: effect of the electronic band structure

The density-matrix renormalization group is used to study the pairing when both electron-electron and electron-phonon interactions are strong in the Holstein-Hubbard model at half filling in a region intermediate between the adiabatic (Migdal's) and antiadiabatic limits. We have found (i) the pairing correlation obtained for a one-dimensional system is nearly degenerate with the charge density-wave correlation in a region where the phonon-induced attraction is comparable with the electron-electron repulsion, but (ii) pairing becomes dominant when we destroy the electron-hole symmetry in a trestle lattice. This provides an instance in which pairing can arise, in a lattice-structure dependent manner, from coexisting electron-electron and electron-phonon interactions.     

Messung der Winkelverteilung und des Wirkungsquerschnittes beim Elementarprozeß der Elektron-Elektron-Bremsstrahlung

By using an electron-photon coincidence technique, we have measured the absolute cross section of electron-electron bremsstrahlung in dependence of the photon emission angle for a definite energy and a definite angle of the outgoing electron. An electron beam of 300 keV was used, incident on a carbon target. Within the experimental errors we find agreement with theoretical calculations. Simultaneously with the electron-electron bremsstrahlung the elementary process of electron-nucleus bremsstrahlung of carbon was measured.     

Temperature and doping dependent flat-band superconductivity on the Lieb-lattice

We consider the superconducting properties of Lieb lattice, which produces a flat-band energy spectrum in the normal state under the strong electron–electron correlation. Firstly, we show the hole-doping dependent superconducting order amplitude with various electron–electron interaction strengths in the zero-temperature limit. Secondly, we obtain the superfluid weight and Berezinskii–Kosterlitz–Thouless(BKT) transition temperature with a lightly doping level. The large ratio between the gap-opening temperature and BKT transition temperature shows similar behavior to the pseudogap state in high-T_c superconductors. The BKT transition temperature versus doping level exhibits a dome-like shape in resemblance to the superconducting dome observed in the high-T_c superconductors. However, unlike the exponential dependence of T_c on the electron–electron interaction strength in the conventional high-T_c superconductors, the BKT transition temperature for a flat band system depends linearly on the electron–electron interaction strength. We also show the doping-dependent superconductivity on a lattice with the staggered hoping parameter in the end. Our predictions are amenable to verification in the ultracold atoms experiment and promote the understanding of the anomalous behavior of the superfluid weight in the high-T_c superconductors.     

Kinetic Approach to the Electrical Conductivity in a Partially Ionized Hydrogen Plasma

The electrical conductivity is investigated for a partially ionized hydrogen plasma, starting from a generalized quantum kinetic equation with three particle collision integrals. To take into account plasma effects, screened potentials are used. The transport cross sections of the considered two and three particle scattering processes are calculated by perturbative solution of the Lippmann-Schwinger equations for the T-matrices up to the second Born approximation. In connection with a mass action law the influence of the electron-electron and the elastic electron-atom scattering is discussed. The pressure ionization (Mott-effect) is described by a minimum-behaviour of the electrical conductivity.     

Eine Koinzidenzmessung zum Elementarprozeß der Elektron-Elektron-Bremsstrahlung bei 300 keV

The absolute cross section of electron-electron bremsstrahlung which is differential in all the free kinematical variables was measured by using an electron-photon coincidence technique. An electron beam of 300 keV was used, incident on a carbon target. Within the experimental errors we found agreement with recent theoretical calculations. Simultaneously with the electron-electron bremsstrahlung the absolute cross section of electron-nucleus bremsstrahlung of carbon was measured.     

氢链中的Peierls机理(Ⅱ)——电子关联对Peierls不稳定性的影响

本文用相关基函数理论研究电子关联对氢链中Peierls不稳定性的影响,结果发现,电子关联使得氢链中的二聚化程度从0.37au减小为0.32au,这说明电子关联只是减弱但不会完全破坏氢链中的Peierls不稳定性,本理论表明,在电子相互作用下链状体系中的Peierls机理依然成立。 关键词：     

Electron-electron interaction in the magnetoresistance of graphene

We investigate the magnetotransport in large area graphene Hall bars epitaxially grown on silicon carbide. In the intermediate field regime between weak localization and Landau quantization, the observed temperature-dependent parabolic magnetoresistivity is a manifestation of the electron-electron interaction. We can consistently describe the data with a model for diffusive (magneto)transport that also includes magnetic-field-dependent effects originating from ballistic time scales. We find an excellent agreement between the experimentally observed temperature dependence of magnetoresistivity and the theory of electron-electron interaction in the diffusive regime. We can further assign a temperature-driven crossover to the reduction of the multiplet modes contributing to electron-electron interaction from 7 to 3 due to intervalley scattering. In addition, we find a temperature-independent ballistic contribution to the magnetoresistivity in classically strong magnetic fields.     

Origin of Bragg-Coulomb high-Tc superconductivity Green''s function and diagram method for umklapp e-e scattering

The Green's function method and diagram technique for umklapp electron-electron scattering mediated by the screened Coulomb interaction in layered anisotropic conductors are examined. Gor'kov-type equations and their general solution for anomalous and normal temperature Green's functions are derived taking into account umklapp scattering of all orders. Explicit equations for dielectric and superconducting order parameters, including coexistent Bragg and BCS pairing, are found. The possibility of the first-order phase transition to the superconducting state is discussed. The theory elucidates the origin of Bragg-Coulomb high-T_c superconductivity, proposed by the authors.     

电子相互作用和孤子元激发(Ⅰ)——电子关联对孤子定域性的影响

研究了电子相互作用对孤子定域性的影响．由于导电聚合物具有宽能带，不宜用Hub-bard模型来描述电子相互作用，需要改用屏蔽库仑势．结果表明，在电子关联对孤子定域性的影响中，屏蔽起了关键作用：弱屏蔽时，电子相互作用会增强孤子的定域性；强屏蔽时，则会削弱其定域性．还从屏蔽与电子关联之间的关系，说明了产生上述结果的物理原因 关键词：     

Probing electron-electron interaction in quantum Hall systems with scanning tunneling spectroscopy

Using low-temperature scanning tunneling spectroscopy applied to the Cs-induced two-dimensional electron system (2DES) on p-type InSb(110), we probe electron-electron interaction effects in the quantum Hall regime. The 2DES is decoupled from bulk states and exhibits spreading resistance within the insulating quantum Hall phases. In quantitative agreement with calculations we find an exchange enhancement of the spin splitting. Moreover, we observe that both the spatially averaged as well as the local density of states feature a characteristic Coulomb gap at the Fermi level. These results show that electron-electron interaction can be probed down to a resolution below all relevant length scales.     

Effective potential for emergent Majorana fermions in superconductor systems

Majorana fermions cannot be found in nature as a free fundamental particle. Nevertheless, in condensed matter systems, they can emerge as a collective excitation. In this work, using functional integration techniques, we calculated the effective potential for emergent Majorana fermions in the Kitaev chain. In this case, we have shown the behavior of the superconductor parameter as a function of temperature. Furthermore, we considered surface-induced superconductivity in a Topological Insulator and calculated the effective potential for emergent Majorana fermions in this system. In the case of an s-wave superconductor, we obtained a gap equation equivalent to that one appearing in a quasi-two-dimensional Dirac electronic system, a candidate to explain high-Tc superconductivity. Finally, for the p-wave superconductor, we have obtained a critical value of the electron-electron interaction in the surface of the Topological Insulator, determining the existence or not of induced superconductivity, a remarkable result to guide experiments.     

Density Correlation Function in a Tunneling Superlattice with Electrons and Holes

We have studied the electron-electron, electron-hole and the hole-hole density correlation functions of the tunneling superlattice with electrons and holes by using the tight-binding envelope functions and taking account of the nearest-neighbor overlap. Based on a newly developed matrix separation technique, these density correlation functions can be explicitly expressed in terms of a matrix density correlation function which allows for a RPA calculation. An effective matrix screened carrier-carrier potential is introduced, which together with the matrix denmty correlation functions given in this paper provides a convenient way to study excitation, transport, and other propertics of a weak tunneling superlattice with both electrons and holes.     

一维半导体高聚物中的激子态和发光性质及局部晶格畸变所产生的影响——Lancos严格对角化方法

应用Lanczos严格对角化方法在具有电子-电子强关联效应的情况下,研究一维高聚物半导体中激子态的能量和波函数的物性,并以此为基础计算了在有局部晶格畸变时激子态的变化及其对发光性质的影响.并发现在一定的互作用参数下,其发光强度与畸变的强度成正比关系. 关键词：