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Search Results: 1 - 10 of 69430 matches for " Xu-Cun Ma "
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Two-Step Oxidation of Pb(111) Surfaces

JIANG Peng,WANG Li-Li,NING Yan-Xiao,QI Yun,MA Xu-Cun,JIA Jin-Feng,XUE Qi-Kun,

中国物理快报 , 2009,
Abstract: We report on a two-step method for oxidation of Pb(111) surfaces, which consists of low temperature (90K) adsorption of O2 and subsequent annealing to room temperature. In situ scanning tunnelling microscopy observation reveals that oxidation of Pb(111) can occur effectively by this method, while direct room temperature adsorption results in no oxidation. Temperature-dependent adsorption behaviour suggests the existence of a precursor state for O2 adsorption on Pb(111) surfaces and can explain the oxidation-resistance of clean Pb(111) surface at room temperature.
Kondo Effect in Self-Assembled Manganese Phthalocyanine Monolayer on Pb Islands

JI Shuai-Hua,FU Ying-Shuang,ZHANG Tong,CHEN Xi,JIA Jin-Feng,XUE Qi-Kun,MA Xu-Cun,

中国物理快报 , 2010,
Modifying Quantum Well States of Pb Thin Films via Interface Engineering

FU Ying-Shuang,JI Shuai-Hua,ZHANG Tong,CHEN Xi,JIA Jin-Feng,XUE Qi-Kun,MA Xu-Cun,

中国物理快报 , 2010,
Abstract: We demonstrate the importance of interface modification on improving electron confinement by preparing Pb quantum islands on Si(111) substrates with two different surface reconstructions, i.e., Si(111)-7× 7 and Si(111)-Root3×Root3-Pb (hereafter, 7× 7 and R3). Characterization with scanning tunneling microscopy/spectroscopy shows that growing Pb films directly on a 7×7 surface will generate many interface defects, which makes the lifetime of quantum well states (QWSs) strongly dependent on surface locations. On the other hand, QWSs in Pb films on an R3 surface are well defined with small variations in linewidth on different surface locations and are much sharper than those on the 7×7 surface. We show that the enhancement in quantum confinement is primarily due to the reduced electron-defect scattering at the interface.
Experimental Proof of Universal Conductance Fluctuation in Quasi-1D Epitaxial Bi$_{2}$Se$_{3}$ Wires
Sadashige Matsuo,Kensaku Chida,Daichi Chiba,Teruo Ono,Keith Slevin,Kensuke Kobayashi,Tomi Ohtsuki,Cui-Zu Chang,Ke He,Xu-Cun Ma,Qi-Kun Xue
Physics , 2013, DOI: 10.1103/PhysRevB.88.155438
Abstract: We report on conductance fluctuation in quasi-one-dimensional wires made of epitaxial Bi$_{2}$Se$_{3}$ thin film. We found that this type of fluctuation decreases as the wire length becomes longer and that the amplitude of the fluctuation is well scaled to the coherence, thermal diffusion, and wire lengths, as predicted by conventional universal conductance fluctuation (UCF) theory. Additionally, the amplitude of the fluctuation can be understood to be equivalent to the UCF amplitude of a system with strong spin-orbit interaction and no time-reversal symmetry. These results indicate that the conductance fluctuation in Bi$_{2}$Se$_{3}$ wires is explainable through UCF theory. This work is the first to verify the scaling relationship of UCF in a system with strong spin-orbit interaction.
Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe$_2$ ultrathin films
Jun-Ping Peng,Jia-Qi Guan,Hui-Min Zhang,Can-Li Song,Lili Wang,Ke He,Qi-Kun Xue,Xu-Cun Ma
Physics , 2014, DOI: 10.1103/PhysRevB.91.121113
Abstract: Molecular beam epitaxy is used to grow TiSe2 ultrathin films on graphitized SiC(0001) substrate. TiSe2films proceed via a nearly layer-by-layer growth mode and exhibit two dominant types of defects, identified as Se vacancy and interstitial, respectively. By means of scanning tunneling microscopy, we demonstrate that the well-established charge density waves can survive in single unit-cell (one triple layer) regime, and find a gradual reduction in their correlation length as the density of surface defects in TiSe2 ultrathin films increases. Our findings offer important insights into the nature of charge density wave in TiSe2, and also pave a material foundation for potential applications based on the collective electronic states.
Probing Dirac Fermion Dynamics in Topological Insulator Bi$_2$Se$_3$ Films with Scanning Tunneling Microscope
Can-Li Song,Lili Wang,Ke He,Shuai-Hua Ji,Xi Chen,Xu-Cun Ma,Qi-Kun Xue
Physics , 2015, DOI: 10.1103/PhysRevLett.114.176602
Abstract: Scanning tunneling microscopy and spectroscopy have been used to investigate the femtosecond dynamics of Dirac fermions in the topological insulator Bi$_2$Se$_3$ ultrathin films. At two-dimensional limit, bulk electrons becomes quantized and the quantization can be controlled by film thickness at single quintuple layer level. By studying the spatial decay of standing waves (quasiparticle interference patterns) off steps, we measure directly the energy and film thickness dependence of phase relaxation length $l_{\phi}$ and inelastic scattering lifetime $\tau$ of topological surface-state electrons. We find that $\tau$ exhibits a remarkable $(E-E_F)^{-2}$ energy dependence and increases with film thickness. We show that the features revealed are typical for electron-electron scattering between surface and bulk states.
Evidence for electron-electron interaction in topological insulator thin films
Jian Wang,Ashley M. DaSilva,Cui-Zu Chang,Ke He,J. K. Jain,Nitin Samarth,Xu-Cun Ma,Qi-Kun Xue,Moses H. W. Chan
Physics , 2010, DOI: 10.1103/PhysRevB.83.245438
Abstract: We consider in our work high quality single crystal thin films of Bi2Se3, grown by molecular beam epitaxy, both with and without Pb doping. Our ARPES data demonstrate topological surface states with a Fermi level lying inside the bulk band gap in the Pb doped filims. Transport data show weak localization behavior, as expected for a 2D system, but a detailed analysis within the standard theoretical framework of diffusive transport shows that the temperature and magnetic field dependences of resistance cannot be reconciled in a theory that neglects inter-electron interactions. We demonstrate that an excellent account of quantum corrections to conductivity is achieved when both disorder and interaction are taken into account. These results clearly demonstrate that it is crucial to include electron electron interaction for a comprehensive understanding of diffusive transport in topological insulators.
Band engineering of Dirac surface states in topological insulators-based van der Waals heterostructures
Cui-Zu Chang,Peizhe Tang,Xiao Feng,Kang Li,Xu-Cun Ma,Wenhui Duan,Ke He,Qi-Kun Xue
Physics , 2015, DOI: 10.1103/PhysRevLett.115.136801
Abstract: The existence of gapless Dirac surface band of a three dimensional (3D) topological insulator (TI) is guaranteed by the non-trivial topological character of the bulk band, yet the surface band dispersion is mainly determined by the environment near the surface. In this Letter, through in-situ angle-resolved photoemission spectroscopy (ARPES) and the first-principles calculation on 3D TI-based van der Waals heterostructures, we demonstrate that one can engineer the surface band structures of 3D TIs by surface modifications without destroying their topological non-trivial property. The result provides an accessible method to independently control the surface and bulk electronic structures of 3D TIs, and sheds lights in designing artificial topological materials for electronic and spintronic purposes.
Unusual giant magnetoresistance effect in heterojunction structure of ultra-thin single-crystal Pb film on silicon substrate
Jian Wang,Xu-Cun Ma,Yun Qi,Ying-Shuang Fu,Shuai-hua Ji,Li Lu,X. C. Xie,Jin-Feng Jia,Xi Chen,Qi-Kun Xue
Physics , 2008, DOI: 10.1088/0957-4484/19/47/475708
Abstract: Superconductor films on semiconductor substrates draw much attention recently since the derived superconductor-based electronics have been shown promising for future data process and storage technologies. By growing atomically uniform single-crystal epitaxial Pb films of several nanometers thick on Si wafers to form a sharp superconductor-semiconductor heterojunction, we have obtained an unusual giant magnetoresistance effect when the Pb film is superconducting. In addition to the great fundamental interest of this effect, the simple structure and compatibility and scalability with current Si-based semiconductor technology offer a great opportunity for integrating superconducting circuits and detectors in a single chip.
Current induced anisotropic magnetoresistance in topological insulator films
Jian Wang,Handong Li,Cui-Zu Chang,Ke He,Joon Sue Lee,Xu-Cun Ma,Nitin Samarth,Qi-Kun Xue,Maohai Xie,M. H. W. Chan
Physics , 2011, DOI: 10.1007/s12274-012-0260-z
Abstract: Topological insulators are insulating in the bulk but possess spin-momentum locked metallic surface states protected by time-reversal symmetry. The existence of these surface states has been confirmed by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). Detecting these surface states by transport measurement, which might at first appear to be the most direct avenue, was shown to be much more challenging than expected. Here, we report a detailed electronic transport study in high quality Bi2Se3 topological insulator thin films. Measurements under in-plane magnetic field, along and perpendicular to the bias current show opposite magnetoresistance. We argue that this contrasting behavior is related to the locking of the spin and current direction providing evidence for helical spin structure of the topological surface states.
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