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Search Results: 1 - 10 of 35303 matches for " Qi-Kun Xue "
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Spin Current Through a Magnetic-Oscillating Quantum Dot
Ping Zhang,Qi-Kun Xue,X. C. Xie
Physics , 2003,
Abstract: Non-equilibrium spin transport through an interacting quantum dot is analyzed. The coherent spin oscillations in the dot provide a generating source for spin current. In the interacting regime, the Kondo effect is influenced in a significant way by the presence of the precessing magnetic field. In particular, when the precession frequency is tuned to resonance between spin up and spin down states of the dot, Kondo singularity for each spin splits into a superposition of two resonance peaks. The Kondo-type cotunneling contribution is manifested by a large enhancement of the pumped spin current in the strong coupling, low temperature regime.
Magnetoresistance of a mesoscopic tunneling quantum dot
Ping Zhang,Qi-Kun Xue,X. C. Xie
Physics , 2002,
Abstract: This paper has been withdrawn by the authors, since the reference citation were not appropriately arranged.
First-principles calculations of Cu(001) thin films: quantum size effect in surface energetics and surface chemical reactivities
Bo Sun,Ping Zhang,Suqing Duan,Xian-Geng Zhao,Junren Shi,Qi-Kun Xue
Physics , 2007, DOI: 10.1103/PhysRevB.75.245422
Abstract: First-principles calculations of Cu(001) free-standing thin films have been performed to investigate the oscillatory quantum size effects exhibited in surface energy, work function, atomic relaxation, and adsorption energy of the cesium adsorbate. The quantum well states have been shown and clarified at particular $k$-points corresponding to the stationary extrema in bulk Brillouin zone, which are in good agreement with experimental observations. The calculated surface energetics and geometry relaxations are clearly featured by quantum oscillations as a function of the film thickness of the film with oscillation periods characterized by a superposition of long and short length scales. Furthermore, we have investigated Cs adsorption onto Cu(001) thin films as a function of the film thickness. Our systematic calculated results clearly show the large-amplitude quantum oscillations in adsorption energetics, which may be used to tailor catalysis, chemical reactions and other surface processes in nanostructured materials.
Generation of spatially-separated spin entanglement in a triple quantum dot system
Ping Zhang,Qi-Kun Xue,Xian-Geng Zhao,X. C. Xie
Physics , 2003, DOI: 10.1103/PhysRevA.69.042307
Abstract: We propose a novel method for the creation of spatially-separated spin entanglement by means of adiabatic passage of an external gate voltage in a triple quantum dot system.
Quantum Entanglement of Excitons in Coupled Quantum Dots
Ping Zhang,C. K. Chan,Qi-Kun Xue,Xian-Geng Zhao
Physics , 2002, DOI: 10.1103/PhysRevA.67.012312
Abstract: Optically-controlled exciton dynamics in coupled quantum dots is studied. We show that the maximally entangled Bell states and Greenberger-Horne-Zeilinger (GHZ) states can be robustly generated by manipulating the system parameters to be at the avoided crossings in the eigenenergy spectrum. The analysis of population transfer is systematically carried out using a dressed-state picture. In addition to the quantum dot configuration that have been discussed by Quiroga and Johnson [Phys. Rev. Lett. \QTR{bf}{83}, 2270 (1999)], we show that the GHZ states also may be produced in a ray of three quantum dots with a shorter generation time.
Spin-Dependent Transport Through An Interacting Quantum Dot
Ping Zhang,Qi-Kun Xue,Yu-Peng Wang,X. C. Xie
Physics , 2002, DOI: 10.1103/PhysRevLett.89.286803
Abstract: We study the nonequilibrium spin transport through a quantum dot containing two spin levels coupled to the magnetic electrodes. A formula for the spin-dependent current is obtained and is applied to discuss the linear conductance and magnetoresistance in the interacting regime, where the so-called Kondo effect arises. We show that the Kondo resonance and the correlation-induced spin splitting of the dot levels may be systematically controlled by internal magnetization in the electrodes. As a result, when the electrodes are in parallel magnetic configuration, the linear conductance is characterized by two spin-resolved peaks. Furthermore, the presence of the spin-flip process in the dot splits the Kondo resonance into three peaks.
Coulomb-enhanced dynamic localization and Bell state generation in coupled quantum dots
Ping Zhang,Qi-Kun Xue,Xian-Geng Zhao,X. C. Xie
Physics , 2002, DOI: 10.1103/PhysRevA.66.022117
Abstract: We investigate the dynamics of two interacting electrons in coupled quantum dots driven by an AC field. We find that the two electrons can be trapped in one of the dots by the AC field, in spite of the strong Coulomb repulsion. In particular, we find that the interaction may enhance the localization effect. We also demonstrate the field excitation procedure to generate the maximally entangled Bell states. The generation time is determined by both analytic and numerical solutions of the time dependent Schrodinger equation.
Interplay between Quantum Size Effect and Strain Effect on Growth of Nanoscale Metal Thin Film
Miao Liu,Yong Han,Lin Tang,Jin-Feng Jia,Qi-Kun Xue,Feng Liu
Physics , 2012, DOI: 10.1103/PhysRevB.86.125427
Abstract: We develop a theoretical framework to investigate the interplay between quantum size effect (QSE) and strain effect on the stability of metal nanofilms. The QSE and strain effect are shown to be coupled through the concept of "quantum electronic stress. First-principles calculations reveal large quantum oscillations in the surface stress of metal nanofilms as a function of film thickness. This adds extrinsically additional strain-coupled quantum oscillations to surface energy of strained metal nanofilms. Our theory enables a quantitative estimation of the amount of strain in experimental samples, and suggests strain be an important factor contributing to the discrepancies between the existing theories and experiments.
Band structure and charge doping effects of potassium-adsorbed FeSe/SrTiO3 system
Fawei Zheng,Li-Li Wang,Qi-Kun Xue,Ping Zhang
Physics , 2015,
Abstract: We theoretically study, through combining the density functional theory and an unfolding technique, the electronic band structure and the charge doping effects for the deposition of potassium (K) on multilayer FeSe films grown on SrTiO3 (001) surface. These results form a theoretical base line for further detailed studies of low-temperature electronic properties and their multiway quantum engineering of FeSe thin films. We explain the Fermi surface topology observed in experiment and formulate the amount of doped electrons as a function of atomic K coverage. We show that the atomic K deposition efficiently dopes electrons to top layer FeSe. Both checkerboard and pair-checkerboard antiferromagnetic (AFM) FeSe layers show electron pockets at M point and no Fermi pocket at $\Gamma$ point with moderate atomic K coverage. The electron transfer from K adsorbate to FeSe film introduces a strong electric field, which leads to a double-Weyl cone structure at M point in the Brillouin zone of checkerboard-AFM FeSe. We demonstrate that with experimentally accessible heavy electron doping, an electron-like Fermi pocket will emerge at $\Gamma$ point, which should manifest itself in modulating the high-temperature superconductivity of FeSe thin films.

Lu Hu,Shen Dian-hong,Deng Xin-f,Xue Qi-kun,N Froumin,M Polak,

中国物理 B , 2001,
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