Richard S. Thompson

Publications (6)27.07 Total impact

• Source

  Available from: ArXiv

  Article: Numerical Calculation of the Fidelity for the Kondo and the Friedel-Anderson Impurities

  Gerd Bergmann, Richard S. Thompson
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  ABSTRACT: The fidelities of the Kondo and the Friedel-Anderson (FA) impurities are calculated numerically. The ground states of both systems are calculated with the FAIR (Friedel artificially inserted resonance) theory. The ground state in the interacting systems is compared with a nullstate in which the interaction is zero. The different multi-electron states are expressed in terms of Wilson states. The use of N Wilson states simulates the use of a large effective number N_{eff} of states. A plot of ln(F) versus N\proptoln(N_{eff}) reveals whether one has an Anderson orthogonality catastrophe at zero energy. The results are at first glance surprising. The ln(F)-ln(N_{eff}) plot for the Kondo impurity diverges for large N_{eff}. On the other hand, the corresponding plot for the symmetric FA impurity saturates for large N_{eff} when the level spacing at the Fermi level is of the order of the singlet-triplet excitation energy. The behavior of the fidelity allows one to determine the phase shift of the electron states in this regime. PACS: 75.20.Hr, 71.23.An, 71.27.+a, 05.30.-d
  The European Physical Journal B - Condensed Matter and Complex Systems. 09/2011; 84(2).
• Article: Continuous-distribution puddle model for conduction in trilayer graphene

  Richard S. Thompson, Yi-Chen Chang, Jia G. Lu
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  ABSTRACT: An insulator-to-metal transition is observed in trilayer graphene based on the temperature dependence of the resistance under different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs. At large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the enhanced electron-phonon scattering. We find that the simple model with overlapping conduction and valence bands, each with quadratic dispersion relations, is unsatisfactory. Instead, we conclude that impurities in the substrate that create local puddles of higher electron or hole densities are responsible for the residual conductivity at low temperatures. The best fit is obtained using a continuous distribution of puddles. From the fit the average of the electron and hole effective masses can be determined.
  08/2011;
• Source

  Available from: arxiv.org

  Article: Weak localization and electron-electron interactions in indium-doped ZnO nanowires.

  Richard S Thompson, Dongdong Li, Christopher M Witte, Jia G Lu
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  ABSTRACT: Single crystal ZnO nanowires doped with indium are synthesized via the laser-assisted chemical vapor deposition method. The conductivity of the nanowires is measured at low temperatures in magnetic fields with directions both perpendicular and parallel to the wire axes. A quantitative fit of our data is obtained, consistent with the theory of a quasi-one-dimensional metallic system with quantum corrections due to weak localization and electron-electron interactions. The anisotropy of the magneto-conductivity agrees with theory. The two quantum corrections are of approximately equal magnitude with respective temperature dependences of T(-1/3)and T(-1/2). The alternative model of quasi-two-dimensional surface conductivity is excluded by the absence of oscillations in the magneto-conductivity in parallel magnetic fields.
  Nano Letters 10/2009; 9(12):3991-5. · 13.20 Impact Factor
• Article: Template‐based Synthesis and Magnetic Properties of Cobalt Nanotube Arrays

  Dongdong Li, Richard S. Thompson, Gerd Bergmann, Jia G. Lu
  Advanced Materials 10/2008; 20(23):4575 - 4578. · 13.88 Impact Factor
• Source

  Available from: ArXiv

  Article: Spacial Modulation of the Magnetization in Cobalt Nanowires

  Gerd Bergmann, Yaqi Tao, Jia G Lu, Richard S. Thompson
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  ABSTRACT: Cobalt nanowires with a diameter in the range between 50 to 100nm can be prepared as single-crystal wires with the easy axis (the c-axis) perpendicular to the wire axis. The competition between the crystal anisotropy and demagnetization energy frustrates the magnetization direction. A periodic modulation of the angle between M and the wire axis yields a lower energy.
  08/2007;
• Source

  Available from: arxiv.org

  Article: Infrared Hall angle in the d-density-wave state: A comparison of theory and experiment

  Sumanta Tewari, Sudip Chakravarty, John O. Fjaerestad, Chetan Nayak, Richard S. Thompson
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  ABSTRACT: Infrared Hall measurements in the pseudogap phase of the high-T-c cuprates are addressed within the framework of the ordered d-density-wave state. The zero-temperature Hall frequency omega(H) is computed as a function of the hole-doping x. Our results are consistent with recent experiments in absolute units. We also discuss the signature of the quantum critical point in the Hall frequency at a critical doping inside the superconducting dome, which can be tested in future experiments.