2,381 research outputs found
Quantum impurity in a Tomonaga-Luttinger liquid: continuous-time quantum Monte Carlo approach
We develop a continuous-time quantum Monte Carlo (CTQMC) method for quantum
impurities coupled to interacting quantum wires described by a
Tomonaga-Luttinger liquid. The method is negative-sign free for any values of
the Tomonaga-Luttinger parameter, which is rigorously proved, and thus,
efficient low-temperature calculations are possible. Duality between electrons
and bosons in one dimensional systems allows us to construct a simple formula
for the CTQMC algorithm in these systems. We show that the CTQMC for
Tomonaga-Luttinger liquids can be implemented with only minor modifications of
previous CTQMC codes developed for impurities coupled to non-interacting
fermions. We apply this method to the Kane-Fisher model of a potential
scatterer in a spin-less quantum wire and to a single spin coupled with the
edge state of a two-dimensional topological insulator assuming an anisotropic
XXZ coupling. Various dynamical response functions such as the electron Green's
function and spin-spin correlation functions are calculated numerically and
their scaling properties are discussed.Comment: 15 pages, 11 figure
Wilson chains are not thermal reservoirs
Wilson chains, based on a logarithmic discretization of a continuous
spectrum, are widely used to model an electronic (or bosonic) bath for Kondo
spins and other quantum impurities within the numerical renormalization group
method and other numerical approaches. In this short note we point out that
Wilson chains can not serve as thermal reservoirs as their temperature changes
by a number of order Delta E when a finite amount of energy Delta E is added.
This proves that for a large class of non-equilibrium problems they cannot be
used to predict the long-time behavior.Comment: 2 page
Non-equilibrium conductance of a three-terminal quantum dot in the Kondo regime: Perturbative Renormalization Group
Motivated by recent experiments, we consider a single-electron transistor in
the Kondo regime which is coupled to three leads in the presence of large bias
voltages. Such a steady-state non-equilibrium system is to a large extent
governed by a decoherence rate induced by the current through the dot. As the
two-terminal conductance turns out to be rather insensitive to the decoherence
rate, we study the conductance in a three-terminal device using perturbative
renormalization group and calculate the characteristic splitting of the Kondo
resonance. The interplay between potential biases and anisotropy in coupling to
the three leads determines the decoherence rate and the conditions for strong
coupling.Comment: 4 pages, 4 figure
Climbing the Entropy Barrier: Driving the Single- towards the Multichannel Kondo Effect by a Weak Coulomb Blockade of the Leads
We study a model proposed recently in which a small quantum dot is coupled
symmetrically to several large quantum dots characterized by a charging energy
E_c. Even if E_c is much smaller than the Kondo temperature T_K, the
long-ranged interactions destabilize the single-channel Kondo effect and induce
a flow towards a multi-channel Kondo fixed point associated with a rise of the
impurity entropy with decreasing temperature. Such an ``uphill flow'' implies a
negative impurity specific heat, in contrast to all systems with local
interactions. An exact solution found for a large number of channels allows us
to capture this physics and to predict transport properties.Comment: 4 pages, 3 figures. Recent references and new title added in
published versio
Breathing Modes and Hidden Symmetry of Trapped Atoms in 2D
Atoms confined in a harmonic potential show universal oscillations in 2D. We
point out the connection of these ''breathing'' modes to the presence of a
hidden symmetry. The underlying symmetry SO(2,1), i.e. the two dimensional
Lorentz group, allows pulsating solutions to be constructed for the interacting
quantum system and for the corresponding nonlinear Gross-Pitaevskii equation.
We point out how this symmetry can be used as a probe for recently proposed
experiments of trapped atoms in 2D.Comment: 4 pages, small changes in title and text, references adde
- …