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Magnetic Properties of Metallic Impurities with Strongly Correlated Electrons

100%
Janiš V., Ringel M.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
30-35
EN
We study the single impurity Anderson model in an external magnetic field. There are no exact results for the spectral function in this situation. Using a resummation of the diagrammatic expansion we demonstrate that the strong coupling regime in a weak magnetic field is Kondo-like with a quasiparticle resonant peak split into two. We find two exponentially small Kondo scales (temperatures), one for transverse and one for longitudinal spin fluctuations. We show that the salient features of the spectral function in the Kondo regime can be seen already within an extended random phase approximation. To reveal the dependence of the Kondo scales on the bare electron interaction, however, one has to employ a two-particle self-consistency with renormalized vertices. We use the parquet approach to derive the dependence of the Kondo scales on magnetic field.
2
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Vertex Corrections to the Electrical Conductivity of the Disordered Falicov-Kimball Model

100%
Pokorný V., Janiš V.
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issue 5
922-923
EN
Quantum coherence of elastically scattered lattice fermions is studied. We calculate vertex corrections to the electrical conductivity of electrons scattered either on thermally equilibrated or statically distributed random impurities and we demonstrate that the sign of the vertex corrections to the Drude conductivity is in both cases negative.
3
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Diagrammatic Perturbation Technique for a Quantum Dot Connected to Superconducting Leads

81%
Pokorný V., Janiš V., Novotný T., Žonda M.
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vol. 126
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issue 1
352-353
EN
We study spectral properties of a quantum dot attached to two superconductors with nonzero phase difference. The system is described as a single-impurity Anderson model coupled to BCS superconducting leads. We utilize diagrammatic perturbation expansion in the Coulomb interaction to capture relevant physical phenomena, particularly the effect of the Coulomb interaction on the Andreev bound states present in the electronic spectrum. Results of the Hartree-Fock and the random phase approximations at zero temperature are presented.
4
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Simplified Parquet Equations for the Anderson Impurity Model: Comparison with Numerically Exact Solutions

81%
Pokorný V., Žonda M., Kauch A., Janiš V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1042-1044
EN
We use an analytic solver for the single-impurity Anderson model based on simplified parquet equations to describe the Kondo asymptotics. This scheme uses a two-particle self-consistency to control the strong-coupling Kondo critical behavior of this model at half filling. The equations can be written in the real-frequency representation, which gives us direct access to spectral functions unlike numerical schemes in the Matsubara formalism. We compare our results to those obtained by second-order perturbation theory, numerical renormalization group, and continuous-time quantum Monte Carlo in order to assess the reliability of this approximation.
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