Publications (6)22.92 Total impact
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ABSTRACT: The paper deals with the nonequilibrium twolead Anderson model, considered as an adequate description for transport through a dc biased quantum dot. Using a selfconsistent equationofmotion method generalized out of equilibrium, we calculate a fourthorder decoherence rate $\gamma^{(4)}$ induced by a bias voltage $V$. This decoherence rate provides a cutoff to the infrared divergences of the selfenergy 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 zerobias peak followed by a broad Coulomb peak at large $V$, reflecting charge fluctuations inside the dot. The lowbias 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  [Show abstract] [Hide abstract]
ABSTRACT: We study the spinvalley 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 spin1∕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 spinvalley degrees of freedom. The density of states (DOS) is obtained as a function of temperature and applied magnetic field using a finiteU equationofmotion 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 tripleelectron Si dots, in a similar fashion to singleelectron ones. The peak structure and splitting patterns are much richer for the spinvalley Kondo effect than for the pure spin Kondo effect.Physical review. B, Condensed matter 11/2007; 76(20). · 3.66 Impact Factor  [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 equationofmotion approach. We show that there is a very complex peak structure near the Fermi energy, with several signatures that distinguish this spinvalley 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 nonconservation is expected to be sampledependent. 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  [Show abstract] [Hide abstract]
ABSTRACT: We investigate classical and quantum physicsbased algorithms for solving the graph isomorphism problem. Our work integrates and extends previous work by Gudkov et al. (condmat/0209112) and by Rudolph (quantph/0206068). Gudkov et al. propose an algorithm intended to solve the graph isomorphism problem in polynomial time by mimicking a classical dynamical manyparticle process. We show that this algorithm fails to distinguish pairs of nonisomorphic 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 nonisomorphic strongly regular graphs that we tested (with up to 29 vertices).Quantum information & computation 01/2005; 5:492506. · 1.63 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: currentproduced (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 (currentproduced), 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 currentproduced 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.NdEuropean Physical Journal C 07/2004; 33(1). · 5.44 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Motivated by recent experimental results, we use a factorization approach to study the threebody B̅ →D(*)KK0 decay modes. Two mechanisms are proposed for kaon pair production: current produced (from a vacuum) and transition (from the B meson). The B0→D(*)+KK0 decay is governed solely by the currentproduced 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 currentproduced and transition processes contribute to B→D(*)0KK0 decays. By using QCD counting rules and the measured B→D(*)0KK0 decay rates, the measured decay spectra can be understood.Physical Review D 02/2003; 67(3). · 4.86 Impact Factor
Publication Stats
43  Citations  
22.92  Total Impact Points  
Top Journals
Institutions

2004–2007

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


2003

National Taiwan University
 Department of Physics
T’aipei, Taipei, Taiwan
