24,335 research outputs found
Conductance of Quantum Impurity Models from Quantum Monte Carlo
The conductance of two Anderson impurity models, one with two-fold and
another with four-fold degeneracy, representing two types of quantum dots, is
calculated using a world-line quantum Monte Carlo (QMC) method. Extrapolation
of the imaginary time QMC data to zero frequency yields the linear conductance,
which is then compared to numerical renormalization group results in order to
assess its accuracy. We find that the method gives excellent results at low
temperature (T<Tk) throughout the mixed valence and Kondo regimes, but it is
unreliable for higher temperature.Comment: 5 pages, 7 figure
Quantum Phase Transition and Dynamically Enhanced Symmetry in Quadruple Quantum Dot System
We propose a system of four quantum dots designed to study the competition
between three types of interactions: Heisenberg, Kondo and Ising. We find a
rich phase diagram containing two sharp features: a quantum phase transition
(QPT) between charge-ordered and charge-liquid phases, and a dramatic resonance
in the charge liquid visible in the conductance. The QPT is of the
Kosterlitz-Thouless type with a discontinuous jump in the conductance at the
transition. We connect the resonance phenomenon with the degeneracy of three
levels in the isolated quadruple dot and argue that this leads to a Kondo-like
dynamical enhancement of symmetry from U(1) x Z_2 to U(1) x U(1).Comment: 4 pages main text + 4 pages supplementary materia
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