Mar 2007, Volume 2 Issue 1
    

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  • Quantum dynamics of tight-binding networks coherently controlled by external fields
    YANG Shuo, SONG Zhi, SUN Chang-pu
    2007, 2(1): 1-16. https://doi.org/10.1007/s11467-007-0001-z
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    With some reviews on the investigations on the schemes for quantum state transfer based on spin systems, we discuss the quantum dynamics of magnetically-controlled networks for Bloch electrons. The networks are constructed by conne
  • Theory of enhanced second-harmonic generation in some artificial materials
    HUANG Ji-ping
    2007, 2(1): 17-30. https://doi.org/10.1007/s11467-007-0002-y
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    We review the recent theoretical investigation on enhanced second-harmonic generation (SHG) in soft nonlinear optical materials based on ferrofluids, graded metallic films, and graded metal-dielectric films of anisotropic particl
  • Mutual Chern-Simons theory and its applications in condensed matter physics
    KOU Su-peng, WENG Zheng-yu, WEN Xiao-gang
    2007, 2(1): 31-35. https://doi.org/10.1007/s11467-007-0004-9
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    In this paper, the mutual Chern-Simons (MCS) theory is introduced as a new kind of topological gauge theory in 2+1 dimensions. We use the MCS theory in gapped phase as an effective low energy theory to describe the Z2
  • Ab initio study of transport properties of an all-carbon molecular switch based on C20 molecule
    OUYANG Fang-ping, XU Hui
    2007, 2(1): 36-40. https://doi.org/10.1007/s11467-007-0003-x
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    Choosing closed-ended armchair (5, 5) single-wall carbon nanotubes (CCNTs) as electrodes, we have investigated the electron transport properties across a carbon molecular junction consisting of a C20 molecule sandwiched
  • Influence of local spin polarization to the Kondo effect
    LI Huan, LI Huan, GUO Wei, GUO Wei
    2007, 2(1): 41-43. https://doi.org/10.1007/s11467-007-0011-x
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    We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer an eigenstate as shown by variational calculations where the splitting of the local energy Δ = εd↑-εd↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.
  • Electronic double refraction due to the Rashba effect: Analytical and numerical results
    SHAO Peng-rui, SHAO Peng-rui, DENG Wen-ji, DENG Wen-ji
    2007, 2(1): 44-50. https://doi.org/10.1007/s11467-007-0015-6
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    By analogy with the classic effect of the double refraction of light, we investigate the relevant effect of an electron entering from the Non-Rashba region to the Rashba region in two-dimensional systems. It is shown that the effect of electronic double refraction is determined by a combined parameter λ=m*λFα/2πh2, rather than both the Rashba coefficient α and wavelength λF of a Fermi electron, separately. For the case of normal incidence, the analytical expressions for the wavefunction of the electron are presented; it is predicted that the Rashba spin-orbit coupling can induce a current perpendicular to the normal incident direction of the electron. Moreover, the general case of incident electron with any given momentum and spin state are studied numerically in detail, including the abrupt changes of spin direction and the two-step characters for reflection.
  • Studies of the doubly degenerate product Jahn-Teller system
    QIU Qing-chun
    2007, 2(1): 51-54. https://doi.org/10.1007/s11467-007-0019-2
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    The static product Jahn-Teller (JT) system with two doubly-degenerate electronic open shells coupling to a single e-mode is further studied in the electronic space using the isostationary function method and the energy min
  • Shot noise in nano-electronic systems under the perturbation of ac fields
    ZHAO Hong-kang
    2007, 2(1): 55-62. https://doi.org/10.1007/s11467-007-0009-4
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    Current noise exists in circuits and electronic devices generally, and it exhibits specific features as the system reaches nanometer size. The noise in the nano-system where external ac fields are applied plays an important role, since the properties of the fields and the nano-system together govern the resulting noise. In this paper, we present the derivation of shot noise by employing the non-equilibrium Green s function technique. The more general formulas for the current correlation and noise spectral density are given. The system is composed of a central nano-system coupled to electrodes, and the obtained noise formulas are related to the Green s functions of detailed central regime and the terminals. As an example, we have performed the numerical calculation on a system with a toroidal carbon nanotube coupled to normal metal leads. The noise and Fano factor show intimate relation with the structure of the system and ac fields. The Aharonov-Bohm-like behaviors on the shot noise spectral density and Fano factor are observed to exhibit oscillation structures with period of quantum flux.
  • Another model for a multiexcitonic quantum dot in an optical microcavity
    SHAN Guang-cun, BAO Shu-ying, HUANG Wei
    2007, 2(1): 63-67. https://doi.org/10.1007/s11467-007-0014-7
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    Very recently, a multiexcitonic quantum dot in an optical microcavity have been theoretically studied [Herbert Vincka, Boris A. Rodriguez, and Augusto Gonzalez, Physica E, 2006, 35: 99-102]. However, due to the inevitable damping losses through the microcavity, in this work, we will present a more precise and sound model in the Lindblad form master equation to investigate the photonic properties of a single quantum dot (QD) in an optical microcavity system, in which the QD may confine the multiexcitons and be in resonant interaction with a single photonic mode of an optical microcavity. The excitation energies, and the properties of the emission photon from the QD microcavity are computed as functions of the exciton-photon coupling strength, detuning, and pump rate. We further compare our results with their results, and find that the calculated intensity of the emitted photon and the spectra crucially depend on the exciton-photon coupling strength g, the photon detuning, and the number of excitons in the QD. Finally, we will give a physical mechanism of the dressed-state picture for the strong coupling between the single mode of an optical microcavity and the QD emitters to explain the details of the emission photon spectra. Our study establishes useful guidelines for the experimental study of such multiexcitonic quantum dot in an optical microcavity system.
  • Evolution of InAs islands in the Stranski-Krastanow mode of InAs/GaAs (001) fabricated using molecular beam epitaxy
    WU Ju, JIN Pen, Lv Xiao-jing, JIAO Yu-heng, WANG Zhan-guo
    2007, 2(1): 68-71. https://doi.org/10.1007/s11467-007-0012-9
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    Based on step-by-step observation using atomic force microscope, two distinctive successive phases were distinguished in accordance with evolution of the three-dimensional InAs islands during the Stranski-Krastanow mode of the InAs/GaAs (001) system fabricated using molecular-beam epitaxy. The initial phase is consistent with a power law, and the latter phase is a comparatively gradual one.
  • Optical properties of low-dimensional structures formed by irradiation of laser
    HUANG Wei-qi, LIU Shi-rong, QIN Chao-jian, CAI Shao-hong, XU Li, WU Ke-yue
    2007, 2(1): 72-75. https://doi.org/10.1007/s11467-007-0017-4
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    Some kinds of low-dimensional nanostructures can be formed by the irradiation of laser on a pure silicon sample and SiGe alloy sample. We have studied the photoluminescence (PL) of the hole-net structure of silicon and the porous structure of SiGe where the PL intensity at 706 nm and 725 nm wavelength increases obviously. The effect of intensity-enhancing in the PL peaks cannot be explained within the quantum confinement alone. We propose a mechanism on the increasing PL emission in the above structures, in which the trap state of the interface between SiO2 and nanocrystal plays an important role.
  • First-principle studies on the electronic structure of Fe3O4(110) surface
    LI Yan-li, LIU Zu-li, YAO Kai-lun
    2007, 2(1): 76-80. https://doi.org/10.1007/s11467-007-0008-5
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    The first-principle was employed to study the six possible models for the Fe3O4 (110) surface, namely the AB-terminated surface (AB model), the AB-terminated with FeA vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-FeA vac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.
  • High-density MgB2 superconducting bulk samples prepared at ambient pressure
    AN Ling, CHEN Chin-ping, FENG Qing-rong, LI Xing-guo
    2007, 2(1): 81-84. https://doi.org/10.1007/s11467-007-0007-6
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    High-density MgB2 (HD-MgB2) superconducting samples (D "e 2.2 g/cm3), using different sources of magnesium powder as raw material, were synthesized in ambient pressure in a rich Mg environment. The magnesium powders used in the fabrication process include nanometer-sized magnesium particles, powders from Alfa Aesar, ordinary off-the-shelf powder, and magnesium chip. The fabrication procedure involved a double-sintering process in a rich-Mg environment. A transition temperature Tc of 39 K was observed. Samples with the equally high density and matching superconducting properties were obtained as well by a triple sintering process of the MgB2 powder directly from Alfa Aesar.
  • What is the highest Tc for phonon-mediated superconductivity?
    CAO Tian-de, GUO Sheng-li, WANG Tie-bang
    2007, 2(1): 85-87. https://doi.org/10.1007/s11467-007-0016-5
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    We suggest that the high-temperature superconductivity can be attributed to the director-roles of the van Hove singularity between an electron-electron interaction and an electron-phonon interaction. The difference between the critical temperature and the pairing temperature is presented, and the Fermi arc, the d-wave symmetry and the poor conductivity, etc., are discussed. In particular, the non-s-wave symmetry is predicted to have the highest Tc for superconductors.
  • Monte Carlo simulations on magnetic behavior of a spin-chain system in triangular lattice doped with antiferromagnetic bonds
    YAO Xiao-yan, LI Peng-lei, DONG Shuai, LIU Jun-ming
    2007, 2(1): 88-91. https://doi.org/10.1007/s11467-007-0018-3
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    A three-dimensional Ising-like model doped with anti-ferromagnetic (AFM) bonds is proposed to investigate the magnetic properties of a doped triangular spin-chain system by using a Monte-Carlo simulation. The simulated results indicate that a steplike magnetization behavior is very sensitive to the concentration of AFM bonds. A low concentration of AFM bonds can suppress the stepwise behavior considerably, in accordance with doping experiments on Ca3Co2O6. The analysis of spin snapshots demonstrates that the AFM bond doping not only breaks the ferromagnetic ordered linear spin chains along the hexagonal c-axis but also has a great influence upon the spin configuration in the ab-plane.
  • Sonochemical preparation and characterization of photochromic MoO3 nanoparticles
    CHEN Jiu-ju, YANG Hai-bin, CHANG Lian-xia, FU Wu-you, ZENG Yi, ZHU Hong-yang, ZOU Guang-tian
    2007, 2(1): 92-95. https://doi.org/10.1007/s11467-007-0013-8
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    The effect of ultrasound irradiation on molybdenum trioxide has been investigated. Under ultrasonic irradiation, spherical-like MoO3 nanoparticles were obtained, while bulk-like MoO3 nanoparticles were prepared without ultrasonic irradiation. The changes in the physicochemical properties of MoO3 have been investigated using techniques such as X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet and visible spectroscopy (UV-vis). The physicochemical changes of MoO3 due to ultrasound irradiation have been attributed to the sonochemical cavity collapse onto the molybdenum trioxide particles. The ultrasonically prepared particles can also greatly improve the photochromism efficiency.
  • Nuclear fusion inside condense matters
    HE Jing-tang
    2007, 2(1): 96-102. https://doi.org/10.1007/s11467-007-0005-8
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    This article describes in detail the nuclear fusion inside condense matters the Fleischmann-Pons effect, the reproducibility of cold fusions, self-consistentcy of cold fusions and the possible applications.
  • O (n ) tricriticality in two dimensions
    GUO Wen-an, Henk W.J. Ble, Bernard Nienhuis
    2007, 2(1): 103-108. https://doi.org/10.1007/s11467-007-0010-y
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    We present exact results for several universal parameters of the tricritical O (n) model in two dimensions. The results apply to the range -2"dn"d3/2, and include the central charge and three scaling dimensions, associated with temperature, magnetic field and the introduction of an interface. Since these results are based on an extrapolation of known relations between the O (n) and the Potts model, they cannot be considered as rigorous. For this reason, we perform an accurate numerical analysis of the central charge and the critical exponents. This analysis, which is based on transfer-matrix calculations on the honeycomb lattice, is in a full and precise agreement with the theoretical predictions.
  • Advances in theoretical models of network science
    FANG Jin-qing, BI Qiao, LI Yong
    2007, 2(1): 109-124. https://doi.org/10.1007/s11467-007-0006-7
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    In this review article, we will summarize the main advances in network science investigated by the CIAE Group of Complex Network in this field. Several theoretical models of network science were proposed and their topological and dynamical properties are reviewed and compared with the other models. Our models mainly include a harmonious unifying hybrid preferential model, a large unifying hybrid network model, a quantum interference network, a hexagonal nanowire network, and a small-world network with the same degree. The models above reveal some new phenomena and findings, which are useful for deeply understanding and investigating complex networks and their applications.