Shiue-yuan Shiau

University of Wisconsin, Madison, Madison, MS, United States

Are you Shiue-yuan Shiau?

Claim your profile

Publications (6)22.57 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The paper deals with the nonequilibrium two-lead Anderson model, considered as an adequate description for transport through a d-c biased quantum dot. Using a self-consistent equation-of-motion method generalized out of equilibrium, we calculate a fourth-order decoherence rate $\gamma^{(4)}$ induced by a bias voltage $V$. This decoherence rate provides a cut-off to the infrared divergences of the self-energy showing up in the Kondo regime. At low temperature, the Kondo peak in the density of states is split into two peaks pinned at the chemical potential of the two leads. The height of these peaks is controlled by $\gamma^{(4)}$. The voltage dependence of the differential conductance exhibits a zero-bias peak followed by a broad Coulomb peak at large $V$, reflecting charge fluctuations inside the dot. The low-bias differential conductance is found to be a universal function of the normalized bias voltage $V/T_K$, where $T_K$ is the Kondo temperature. The universal scaling with a single energy scale $T_K$ at low bias voltages is also observed for the renormalized decoherence rate $\gamma^{(4)}/T_K$. We discuss the effect of $\gamma^{(4)}$ on the crossover from strong to weak coupling regime when either the temperature or the bias voltage is increased.
    Physical review. B, Condensed matter 01/2010; 81(16). · 3.66 Impact Factor
  • Shiue-yuan Shiau, Robert Joynt
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the spin-valley Kondo effect of a silicon quantum dot occupied by N electrons, with N up to 4. We show that the Kondo resonance appears in the N=1,2,3 Coulomb blockade regimes, but not in the N=4 one, in contrast to the spin-1∕2 Kondo effect, which only occurs at N=odd. Assuming large orbital level spacings, the energy states of the dot can be simply characterized by fourfold spin-valley degrees of freedom. The density of states (DOS) is obtained as a function of temperature and applied magnetic field using a finite-U equation-of-motion approach. The structure in the DOS can be detected in transport experiments. The Kondo resonance is split by the Zeeman splitting and valley splitting for double- and triple-electron Si dots, in a similar fashion to single-electron ones. The peak structure and splitting patterns are much richer for the spin-valley Kondo effect than for the pure spin Kondo effect.
    Physical review. B, Condensed matter 11/2007; 76(20). · 3.66 Impact Factor
  • Source
    Shiue-yuan Shiau, Sucismita Chutia, Robert Joynt
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent progress in the fabrication of quantum dots using silicon opens the prospect of observing the Kondo effect associated with the valley degree of freedom. We compute the dot density of states using an Anderson model with infinite Coulomb interaction $U$, whose structure mimics the nonlinear conductance through a dot. The density of states is obtained as a function of temperature and applied magnetic field in the Kondo regime using an equation-of-motion approach. We show that there is a very complex peak structure near the Fermi energy, with several signatures that distinguish this spin-valley Kondo effect from the usual spin Kondo effect seen in GaAs dots. We also show that the valley index is generally not conserved when electrons tunnel into a silicon dot, though the extent of this non-conservation is expected to be sample-dependent. We identify features of the conductance that should enable experimenters to understand the interplay of Zeeman splitting and valley splitting, as well as the dependence of tunneling on the valley degree of freedom.
    Physical Review B 12/2006; · 3.66 Impact Factor
  • Source
    Shiue-yuan Shiau, Robert Joynt, Susan N. Coppersmith
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate classical and quantum physics-based algorithms for solving the graph isomorphism problem. Our work integrates and extends previous work by Gudkov et al. (cond-mat/0209112) and by Rudolph (quant-ph/0206068). Gudkov et al. propose an algorithm intended to solve the graph isomorphism problem in polynomial time by mimicking a classical dynamical many-particle process. We show that this algorithm fails to distinguish pairs of non-isomorphic strongly regular graphs, thus providing an infinite class of counterexamples. We also show that the simplest quantum generalization of the algorithm also fails. However, by combining Gudkov et al.'s algorithm with a construction proposed by Rudoph in which one examines a graph describing the dynamics of two particles on the original graph, we find an algorithm that successfully distinguishes all pairs of non-isomorphic strongly regular graphs that we tested (with up to 29 vertices).
    Quantum information & computation 01/2005; 5:492-506. · 1.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Motivated by experimental results on $\overline B\to D^{(*)}K^{-}K^{0}$ , we use a factorization approach to study these decays. Two mechanisms concerning kaon pair production arise: current-produced (from vacuum) and transition (from the B meson). The kaon pair in the $\overline B {}^0\to D^{(*)+}K^{-}K^0$ decays can be produced only by the vector current (current-produced), whose matrix element can be extracted from $e^+e^{-}\to K\overline K$ processes via isospin relations. The decay rates obtained this way are in good agreement with experiment. The B –→ D (*)0K –K 0 decays involve both current-produced and transition processes. By using QCD counting rules and the measured B –→ D (*)0K –K 0 decay rates, the measured decay spectra can be understood. PACS: 13.25.Hw – 14.40.Nd
    European Physical Journal C 07/2004; 33(1). · 5.25 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Motivated by recent experimental results, we use a factorization approach to study the three-body B̅ →D(*)K-K0 decay modes. Two mechanisms are proposed for kaon pair production: current produced (from a vacuum) and transition (from the B meson). The B0→D(*)+K-K0 decay is governed solely by the current-produced mechanism. As the kaon pair can be produced only by the vector current, the matrix element can be extracted from e+e-→KK̅ processes via isospin relations. The decay rates obtained this way are in good agreement with experiment. Both current-produced and transition processes contribute to B-→D(*)0K-K0 decays. By using QCD counting rules and the measured B-→D(*)0K-K0 decay rates, the measured decay spectra can be understood.
    Physical Review D 02/2003; 67(3). · 4.69 Impact Factor