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.     

GaP中N和NNi对等电子陷阱态的压力行为

 半导体中的局域电子态和半导体的能带结构密切相关，揭示局域电子态和能带结构之间的内在关系是当前半导体电子理论的重要方面。而压力光谱实验对研究这种相互关系提供了重要手段。本文对GaP中深、浅两组能级的不同压力行为作了系统的实验研究。实验观察到无论在室温还是在低温，压力小于3.3 GPa时，以N陷阱束缚激子的发光过程为主，大于3.3 GPa时则以自由激子零声子过程为主，并且所有与N有关的陷阱态都具有压力的非线性行为。根据有效质量随压力的变化提出能谷中不同能量态具有不同的压力关系。基于有效质量随压力变化的能带格林函数方法，对N和NNi对的压力系数作了模型计算，其结果和陷阱态的压力行为符合得相当好。证实了带结构，尤其是能谷曲率随压力的变化是决定陷阱态压力行为的主要因素。     

Surface-induced orbital-selective band reconstruction in kagome superconductor CsV3Sb5

The two-dimensional (2D) kagome superconductor CsV₃Sb₅ has attracted much recent attention due to the coexistence of superconductivity, charge orders, topology and kagome physics, which manifest themselves as distinct electronic structures in both bulk and surface states of the material. An interesting next step is to manipulate the electronic states in this system. Here, we report angle-resolved photoemission spectroscopy (ARPES) evidence for a surface-induced orbital-selective band reconstruction in CsV₃Sb₅. A significant energy shift of the electron-like band around Γ and a moderate energy shift of the hole-like band around M are observed as a function of time. This evolution is reproduced in a much shorter time scale by in-situ annealing of the CsV₃Sb₅ sample. Orbital-resolved density functional theory (DFT) calculations reveal that the momentum-dependent band reconstruction is associated with different orbitals for the bands around Γ and M, and the time-dependent evolution points to the change of sample surface that is likely caused by the formation of Cs vacancies on the surface. Our results indicate the possibility of orbital-selective control of the band structure via surface modification, which may open a new avenue for manipulating exotic phenomena in this material system, including superconductivity.     

The Effect of Ammonia Ions on the Absorption and Fluorescence of an Oxazine Dye

The addition of ammonium hydroxide to a weakly acidic oxazine perchlorate dye produces a color change by means of a deprotonation mechanism in which the hydroxyl radical abstracts a loosely bound proton, leaving the positively charged ammonium cation to counter balance the perchlorate anion. This reaction produces significant absorption and fluorescence band shifts which can be accounted for by a semi-classical oscillator model predicting two dichroic electronic band systems associated with this dye. Peculiar wavelength excitation dependent fluorescence band shifts are attributed to overlapping triplet states simultaneously excited.     

Bulk electronic structure of metals resolved with scanning tunneling microscopy

We demonstrate that bulk band structure can have a strong influence in scanning tunneling microscopy measurements by resolving electronic interference patterns associated with scattering phenomena of bulk states at a metal surface and reconstructing the bulk band topology. Our data reveal that bulk information can be detected because states at the edge of the surface-projected bulk band have a predominant role on the scattering patterns. With the aid of density functional calculations, we associate this effect with an intrinsic increase in the projected density of states of edge states. This enhancement is characteristic of the three-dimensional bulk band curvature, a phenomenon analog to a van Hove singularity.     

电子相互作用对聚乙炔中极化子电子态的影响

本文根据SSH和Hubbard模型研究了电子相互作用对聚乙炔中极化子的电子态的影响。结果发现:1.电子相互作用使能隙中出现了一个新的电子束缚态,它是靠近价带的浅能级;2.电子相互作用使得价带下面的一个电子束缚态消失,同时在导带上面出现了两个电子束缚态。 关键词：     

Surface-state localization at adatoms

Low-temperature scanning tunneling spectroscopy of magnetic and nonmagnetic metal atoms on Ag(111) and on Cu(111) surfaces reveals the existence of a common electronic resonance at an energy below the binding energies of the surface states. Using an extended Newns-Anderson model, we assign this resonance to an adsorbate-induced bound state, split off from the bottom of the surface-state band, and broadened by the interaction with bulk states. A line shape analysis of the bound state indicates that Ag and Cu adatoms on Ag(111) and Cu(111), respectively, decrease the surface-state lifetime, while a cobalt adatom causes no significant change.     

Une méthode de pseudopotentiel appliquée aux fonctions d'onde de surface

A new variant of the pseudopotentiel method is suggested. If the volume band structure is known, this method enables an appreciable simplification for the calculation of surface electronic states and for the determination of complex band structure, and gives correct results even in the case of bound electrons.     

Electronic energy levels in semiconductor quantum wells and superlattices

We present the results of the calculations of some electronic properties of semiconductor quantum wells and superlattices. The review includes the superlattice band structure and the quantum well bound energy levels; the virtual bound states of semiconductor quantum wells and their influence on the energy spectrum of separate confinement heterostructures. Finally the perturbation of quantum well bound states and exciton states by a static electric field applied parallel to the growth axis is considered.     

On the local densities of states on flat and stepped Pt surfaces

The electronic structure of the d band of both flat and stepped Pt surfaces is investigated within the tight-binding approximation, using a moment method. A sharp surface virtual bound state peak is found in the local density of states at the protruding edge of the stepped surfaces and the symmetry of states near the Fermi level are found to be rather dependent on the geometry of the surface. Possible connections with experiments are briefly discussed.     

FeVO_4电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了三斜结构FeVO_4的结构,基态的能带结构、总态密度和分波态密度.将FeVO_4非共线的螺旋磁结构简化为六种不同的反铁磁结构,通过比较不同自旋构型的总能确定了基态磁结构.能带计算和总态密度结果均显示FeVO_4是能隙为2.19 e V的半导体,与实验结果相符.考虑Fe原子的在位库仑能,FeVO_4的能带结构和态密度都发生变化,说明FeVO_4晶体是一个典型的强关联电子体系.     

Effects of the second and third neighbor hopping interactions on the electronic states of soliton in polyacetylene

We have studied the energy spectra and the electronic states of a soliton in the weakly coupled electron-phonon systems using an extension of SSH model that includes non-nearest neighbor hopping interactions. The results show that: (1) the electron-hole symmetry of the energy band structure implied by SSH model is broken, and the energy gap 2 increases. (2) for a negative charged soliton, only two bound states have been found, one of them is the midgap state, another is a new shallow state near the bottom of the conduction band; for a neutral soliton, all three bound states exist as in the SSH model, but their localizations are strengthened; for a positive charged soliton, four bound states have been found, one of which is an additional state near the top of the conduction band.     

Molecule opacity study on low-lying states of CS

CS molecule, which plays a key role in atmospheric and astrophysical circumstances, has drawn great attention for long time. Owing to its large state density, the detailed information of the electronic structure of CS is still lacking. In this work, the high-level MRCI+Q method is used to compute the potential energy curves, dipole moments and transition dipole moments of singlet and triplet states correlated with the lowest dissociation limit of CS, based on which high accurate vibration—rotation levels and spectroscopic constants of bound states are evaluated. The opacity of CS relevant to atmospheric circumstance is computed at a pressure of 100 atms for different temperatures. With the increase of temperature, band systems from different transitions mingle with each other, and band boundaries become blurred, which are originated from the increased population on vibrational excited states and electronic excited states at high temperature.     

Ab initio potential energy curves for the CO+ ion and a study of the photoelectron spectra of CO

The potential energy curves for the low-lying electronic states of CO⁺ are calculated by using the ab initio full valence configuration interaction method with minimal STOs. Calculated spectroscopic parameters are given for twenty five bound states, and the compared with the experimental values for four observed bound states. The band systems, observed in the 22 eV and 27 eV region of He II photoelectron spectra of CO, are analysed by using calculated potential energy curves and spectral intensities. New assignment for the fourth band system at 22 eV ～ 23 eV is proposed.     

Surface electronic structure of SnO2(110)

We report theoretical investigations on the surface electronic structure of the (110)-face of SnO₂, a semiconductor of rutile bulk structure. Starting with a tight binding Hamiltonian for the bulk, we determine the surface electronic structure using the scattering theoretic method. As results we obtain the surface bound states, the surface resonances and the wave-vector resolved surface layer densities of states. The dominant features are two backbond states in the stomach gap of the main valence band and two Sn-s derived states in the lower conduction band region. In the upper valence band region, only weak resonances occur, like in other materials with relatively strong ionicity.     

Evolution of electronic states in thin Ca(001) flms in strong electrostatic fields

The transformation of electronic states in Ca(001) films in strong electrostatic fields is studied using electron density functional theory. It is shown that an excess film charge of either sign pins the Fermi level (with respect to the conduction band edge) in a wide range of fields. For positively charged films, the change in the density of states at the Fermi level is small but the energy derivative of the density of states changes sign with increasing excess charge of the film. For negatively charged Ca(001) films, the change in the density of states at the Fermi level plays the main role in stabilizing the width of the occupied part of the conduction band; this should be manifested in the electronic thermodynamic and transport properties of negatively charged Ca(001) films with quantum confinement.     

Temperature and concentration dependences of the electronic etructure of copper oxides in the generalized tight binding method

The electronic structure of p-type doped HTSC cuprates is calculated by explicitly taking into account strong electron correlations. The smooth evolution of the electronic structure from undoped antiferro-magnetic to optimally and heavily doped paramagnetic compositions is traced. For a low doping level, in-gap impurity-type states are obtained, at which the Fermi level is pinned in the low-doping region. These states are separated by a pseudogap from the valence band. The Fermi surfaces calculated for the paramagnetic phase for various concentrations of holes are in good agreement with the results of ARPES experiments and indicate a gradual change in the Fermi surface from the hole type to the electron type.     

Photoemission yield spectroscopy of electronic surface states on germanium (111) surfaces

The electronic surface states of cleaved and annealed Ge(111) surfaces have been investigated by photoemission yield spectroscopy and contact potential measurements on a set of differently doped samples. On the 2 × 1 cleaved surface, a surface state band centered about 0.7 eV below the valence band maximum is found. The variations of the work function with the doping level show that an empty surface state band exists above the Fermi level. After annealing at temperatures of the order of 350°C, this surface exhibits a 2 × 8 superstructure. A new surface state band is then found closer to the valence band maximum. This variation of the surface state distribution is correlated to a change in the surface potential. The variation of the electronic characteristics upon oxygen adsorption are also reported and an evaluation of the sticking coefficient is made for both structures.     

MgxZn1-xO结构性质

采用第一性原理计算模拟了不同组分的Mg_xZn_1-xO半导体混晶的晶格常数、总能、结构,以及禁带宽度的变化。计算结果显示,随着Mg组分的增加,晶格常数逐渐减小,晶体逐渐偏离纤锌矿结构。对各种不同的Mg原子排列情况进行比较认为,Mg_xZn_1-xO的结构随组分x的增大,发生从纤锌矿到岩盐矿的结构相变的可能性高于发生相分离。另一方面,禁带宽度随组分增大主要由价带顶的移动所致。进一步分析Mg原子各种电子态对价带的影响表明,Mg对价带顶附近能带的贡献依次来自p、d、s态电子。随着组分x的增加,p态电子在价带顶附近的密度明显提高,说明sp轨道杂化不但对晶体的几何结构产生影响,而且对其电子结构也起重要作用。     

Itinerant Topological Magnons in SU (2) Symmetric Topological Hubbard Models with Nearly Flat Electronic Bands

We show that a suitable combination of flat-band ferromagnetism,geometry and nontrivial electronic band topology can give rise to itinerant topological magnons.An SU(2) symmetric topological Hubbard model with nearly flat electronic bands,on a Kagome lattice,is considered as the prototype.This model exhibits ferromagnetic order when the lowest electronic band is half-filled.Using the numerical exact diagonalization method with a projection onto this nearly flat band,we can obtain the magnonic spectra.In the flat-band limit,the spectra exhibit distinct dispersions with Dirac points,similar to those of free electrons with isotropic hoppings,or a local spin magnet with pure ferromagnetic Heisenberg exchanges on the same geometry.Significantly,the non-flatness of the electronic band may induce a topological gap at the Dirac points,leading to a magnonic band with a nonzero Chern number.More intriguingly,this magnonic Chern number changes its sign when the topological index of the electronic band is reversed,suggesting that the nontrivial topology of the magnonic band is related to its underlying electronic band.Our work suggests interesting directions for the further exploration of,and searches for,itinerant topological magnons.