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Real-space structure of the impurity screening cloud in the Resonant Level Model

Shreyoshi Ghosh, Pedro Ribeiro, Masudul Haque

Published Apr 1, 2014• 23 citations
OpenAlex

Abstract

We present a detailed investigation of the impurity screening cloud in the Resonant Level Model. The screening is visible in the structure of impurity-bath correlators as a function of distance from the impurity. We characterize the screening cloud through scaling analyses of impurity-bath correlators and entanglement entropies. We devise and study several situations where the screening cloud is destroyed or modified: finite temperatures, energetic detuning of the impurity from the chemical potential, and the situation of an unconventional bath with diverging density of states. ar X iv

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Real-space structure of the impurity screening cloud in the resonant level model

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We present a detailed investigation of the impurity screening cloud in the resonant level model. The screening is visible in the structure of impurity–bath correlators as a function of distance from the impurity. We characterize the screening cloud through scaling analyses of impurity–bath correlators and entanglement entropies. We devise and study several situations where the screening cloud is destroyed or modified: finite temperatures, energetic detuning of the impurity from the chemical potential, and the situation of an unconventional bath with diverging density of states.

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Dynamical quantum impurities in metals induce electronic correlations in real space that are difficult to simulate due to their multiscale nature, so that only $s\text{\ensuremath{-}}\mathrm{wave}$ scattering in clean metallic hosts has been investigated so far. However, screening clouds should show anisotropy due to lack of full rotational invariance in two- and three-dimensional lattices, while inherent disorder will also induce spatial inhomogeneities. To tackle these challenges, we present an efficient and robust algorithm based on the recursive generation of natural orbitals defined as eigenvectors of the truncated single-particle density matrix. This method provides well-converged many-body wave functions on lattices with up to tens of thousands of sites, bypassing some limitations of other approaches. The algorithm is put to the test by investigating the charge screening cloud around an interacting resonant level, both on clean and disordered lattices, achieving accurate spatial resolution from short to long distances. We thus demonstrate strong anisotropy of spatial correlations around an adatom in the half-filled square lattice. Taking advantage of the efficiency of the algorithm, we further compute the disorder-induced distribution of Kondo temperatures over several thousands of random realizations, at the same time gaining access to the full spatial profile of the screening cloud in each sample. While the charge screening cloud is typically shortened due to the polarization of the impurity by the disorder potential, we surprisingly find that rare disorder configurations preserve the long-range nature of Kondo correlations in the electronic bath.

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Kondo screening cloud in the single-impurity Anderson model: A DMRG study

Andreas Holzner, Ian P. McCulloch, Ulrich Schollwöck +2 more

A magnetic moment in a metal or in a quantum dot is, at low temperatures, screened by the conduction electrons through the mechanism of the Kondo effect. This gives rise to spin-spin correlations between the magnetic moment and the conduction electrons, which can have a substantial spatial extension. We study this phenomenon, the so-called Kondo cloud, by means of the density matrix renormalization group method for the case of the single-impurity Anderson model. We focus on the question whether the Kondo screening length, typically assumed to be proportional to the inverse Kondo temperature, can be extracted from the spin-spin correlations. For several mechanisms -- the gate potential and a magnetic field -- that destroy the Kondo effect, we investigate the behavior of the screening cloud induced by these perturbations.

•Jun 16, 2009•0 citations
We present a detailed investigation of the impurity screening cloud in the Resonant Level Model. The screening is visible in the structure of impurity-bath correlators as a function of distance from the impurity. We characterize the screening cloud through scaling analyses of impurity-bath correlators and entanglement entropies. We devise and study several situations where the screening cloud is destroyed or modified: finite temperatures, energetic detuning of the impurity from the chemical potential, and the situation of an unconventional bath with diverging density of states. ar X iv
We present a detailed investigation of the impurity screening cloud in the resonant level model. The screening is visible in the structure of impurity–bath correlators as a function of distance from the impurity. We characterize the screening cloud through scaling analyses of impurity–bath correlators and entanglement entropies. We devise and study several situations where the screening cloud is destroyed or modified: finite temperatures, energetic detuning of the impurity from the chemical potential, and the situation of an unconventional bath with diverging density of states.
Dynamical quantum impurities in metals induce electronic correlations in real space that are difficult to simulate due to their multiscale nature, so that only $s\text{\ensuremath{-}}\mathrm{wave}$ scattering in clean metallic hosts has been investigated so far. However, screening clouds should show anisotropy due to lack of full rotational invariance in two- and three-dimensional lattices, while inherent disorder will also induce spatial inhomogeneities. To tackle these challenges, we present an efficient and robust algorithm based on the recursive generation of natural orbitals defined as eigenvectors of the truncated single-particle density matrix. This method provides well-converged many-body wave functions on lattices with up to tens of thousands of sites, bypassing some limitations of other approaches. The algorithm is put to the test by investigating the charge screening cloud around an interacting resonant level, both on clean and disordered lattices, achieving accurate spatial resolution from short to long distances. We thus demonstrate strong anisotropy of spatial correlations around an adatom in the half-filled square lattice. Taking advantage of the efficiency of the algorithm, we further compute the disorder-induced distribution of Kondo temperatures over several thousands of random realizations, at the same time gaining access to the full spatial profile of the screening cloud in each sample. While the charge screening cloud is typically shortened due to the polarization of the impurity by the disorder potential, we surprisingly find that rare disorder configurations preserve the long-range nature of Kondo correlations in the electronic bath.
Abstract The screening of an impurity spin in the Kondo model occurs over a characteristic length scale ξ K , that defines the size of the Kondo screening cloud or ‘mist’. The presence of such a length scale in experimental and numerical results is rather subtle. A consistent way to show the presence of the screening cloud is to demonstrate scaling in the spatial correlations in terms of the single variable, r / ξ K instead of the correlations depending on r and ξ K separately. Here we study the paradigmatic one channel Kondo model using a spin chain representation, with an impurity spin at one end of the chain coupled with a strength J K ′ . Using Fermi liquid theory combined with numerical results, we obtain new high precision estimates of the non-universal terms in the entanglement entropy which leads to a verification of the expected non-integer ground-state degeneracy, g. This then allows us to study the impurity contribution to the entanglement in detail. If the impurity coupling J K ′ is varied, a precise determination of ξ K can then be obtained. The length scale, ξ K , is then shown to characterize the scaling of both the uniform and alternating part of a measure of the magnetization of part of an odd length chain.
The screening of an impurity spin by conduction electrons is associated with the formation of a large Kondo screening cloud, of size ξ K . We study the quantum entanglement between a region of size r surrounding the impurity and the rest of the sample (of total size R ) using density matrix renormalization group and analytic methods. The corresponding ‘impurity entanglement entropy’, S imp , is shown to be a universal scaling function of r /ξ K and r / R . We calculate this universal function using Fermi liquid theory in the regime ξ K ≪ r .
A magnetic moment in a metal or in a quantum dot is, at low temperatures, screened by the conduction electrons through the mechanism of the Kondo effect. This gives rise to spin-spin correlations between the magnetic moment and the conduction electrons, which can have a substantial spatial extension. We study this phenomenon, the so-called Kondo cloud, by means of the density matrix renormalization group method for the case of the single-impurity Anderson model. We focus on the question whether the Kondo screening length, typically assumed to be proportional to the inverse Kondo temperature, can be extracted from the spin-spin correlations. For several mechanisms---the gate potential and a magnetic field---which destroy the Kondo effect, we investigate the behavior of the screening cloud induced by these perturbations.
A magnetic moment in a metal or in a quantum dot is, at low temperatures, screened by the conduction electrons through the mechanism of the Kondo effect. This gives rise to spin-spin correlations between the magnetic moment and the conduction electrons, which can have a substantial spatial extension. We study this phenomenon, the so-called Kondo cloud, by means of the density matrix renormalization group method for the case of the single-impurity Anderson model. We focus on the question whether the Kondo screening length, typically assumed to be proportional to the inverse Kondo temperature, can be extracted from the spin-spin correlations. For several mechanisms -- the gate potential and a magnetic field -- that destroy the Kondo effect, we investigate the behavior of the screening cloud induced by these perturbations.