Kondo effect in the presence of van Hove singularities: A numerical renormalization group study

Zhuravlev, A. K.; Irkhin, V. Yu.

doi:10.1103/physrevb.84.245111

Cited by 15 publications

(31 citation statements)

References 49 publications

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“…3(b) and 3(c)], over which range T K is almost constant, χ imp changes sign at T ≃ T K /2 and then approaches zero from below. Such a sign change, seen in other systems with strong variation of the hybridization near the chemical potential [39][40][41] but generally without associated QPTs , arises from the discon-…”

Section: (B) Described By An Anderson Hamiltonianhmentioning

confidence: 96%

Quantum phase transitions into Kondo states in bilayer graphene

et al. 2014

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We study a magnetic impurity intercalated in bilayer graphene. A representative configuration generates a hybridization function with strong dependence on the conduction-electron energy, including a full gap with one hard and one soft edge. Shifts of the chemical potential via gating or doping drive the system between non-Kondo (free-moment) and Kondo-screened phases, with strong variation of the Kondo scale. Quantum phase transitions near the soft edge are of KosterlitzThouless type, while others are first order. Near the hard edge, a bound-state singlet appears inside the gap; although of single-particle character, its signatures in scanning tunneling spectroscopy are very similar to those arising from a many-body Kondo resonance.PACS numbers: 72.15. Qm, 73.22.Pr, 75.20.Hr, 64.70.Tg One of the remarkable manifestations of cooperative phenomena in condensed matter is the many-body screening of a magnetic impurity in a nonmagnetic metal. This Kondo effect, well understood in ordinary metals [1], acquires added complexity in cases where the host density of states (DOS) varies strongly with energy E near the chemical potential µ. The pseudogap Kondo problem [2-6] with a DOS ρ(E) ∝ |E − µ| r (realized, for example, for r = 1 in high-temperature superconductors [7]) exhibits a rich phase diagram that depends on the band exponent r, the impurity-host exchange coupling J, and the presence or absence of particle-hole (p-h) symmetry.Similar DOS features can also appear in lowdimensional systems such as graphene [8]. The technologically and conceptually important issue of creating localized magnetic moments in monolayer graphene, and the appearance of the Kondo effect, have been the focus of many recent theoretical [9][10][11][12][13][14][15][16][17][18][19][20] and experimental [21][22][23][24] studies, with controversial results (see [25] for an overview). A more complex DOS appears in bilayer graphene (BLG), a material that can be gapped by gating, and thus has attracted much attention for possible device applications [26]. The variety of microscopic environments for magnetic impurities combined with easy tunability, make BLG highly promising for the study of quantum phase transitions (QPTs) into various Kondo states [27,28].This paper explores such QPTs for a representative configuration of an intercalated spin σ = 1/2 magnetic impurity in BLG. This setup is described by an Anderson impurity model with an energy-dependent hybridization featuring a gap that has one hard and one soft edge. Under variation of the chemical potential µ, the system passes from a free-moment (FM) phase to a Kondo phase featuring a strong µ dependence of the Kondo temperature scale. The QPTs found near the soft hybridization edge are of Kosterlitz-Thouless type, while all other QPTs are first order. We present thermodynamic and spectral properties near these QPTs, and discuss some of their consequences for spectroscopy measurements. For µ near the hard hybridization edge, the FM phase exhibits a singlet bound state inside the gap. This bo...

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Section: (B) Described By An Anderson Hamiltonianhmentioning

confidence: 96%

Quantum phase transitions into Kondo states in bilayer graphene

et al. 2014

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“…10c). In close proximity to singularities, however, the presented results should be treated with caution, only as a visualization of tendencies due to a break of applicability of SBMFA in the range of of divergent self-energy [101]. …”

Section: Electrodes With Singular Electron Spectrummentioning

confidence: 97%

Spin-orbital and spin Kondo effects in parallel coupled quantum dots

Krychowski

Lipiński

2016

Phys. Rev. B

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Strong electron correlations and interference effects are discussed in parallel-coupled single-level and orbitally doubly degenerate quantum dots. The finite-U mean-field slave boson approach is used to study many-body effects. The analysis is carried out in a wide range of parameter space including both atomic-like and molecular-like Kondo regimes and taking into account various perturbations, like interdot tunneling, interdot interaction, mixing of the electrode channels and exchange interaction. We also discuss the influence of singularities of electronic structure and the impact of polarization of electrodes. Special attention is paid to potential spintronic applications of these systems showing how current polarization can be controlled by adjusting interference conditions and correlations by gate voltage. Simple proposals of double dot spin valve and bipolar electrically tunable spin filter are presented.

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“…In this case, extreme caution should be exercised when applying Wilson's definition, because the impurity susceptibility, being defined through global quantities, involves a subtlety from the conduction bath such that it may not necessarily yield the intrinsic spin dynamics of the impurity. Particularly, a negative χ imp was found by the calculations [11][12][13][14], signaling a diamagnetic Kondo impurity, even with non-Fermi-liquid behavior violating the low-temperature plateau in χ imp [11,12]. This is inconsistent with one's intuition.…”

Section: Introductionmentioning

confidence: 75%

“…This is inconsistent with one's intuition. We emphasize that in those systems [11][12][13][14], though strongly energy dependent, the conduction bands are not gapped at the Fermi energy. Therefore, the impurity Kondo physics is very likely to be still conventional, without the exotic non-Fermi-liquid and diamagnetic behaviors (gapped bands [16] could, of course, lead to non-Fermi-liquid behavior).…”

Section: Introductionmentioning

confidence: 80%

“…However, the nature of the electron bath in the Kondo problem varies from one realization to another. It may possess a band of strong energy dependence, as in magnetic impurities adsorbed on graphene [11] and square lattice [12], double quantum dots [13], the narrow-band Anderson model [14], and so on, for which the two susceptibilities may differ significantly [15]. In this case, extreme caution should be exercised when applying Wilson's definition, because the impurity susceptibility, being defined through global quantities, involves a subtlety from the conduction bath such that it may not necessarily yield the intrinsic spin dynamics of the impurity.…”

Section: Introductionmentioning

confidence: 99%

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Spin susceptibility of Anderson impurities in arbitrary conduction bands

et al. 2015

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Spin susceptibility of Anderson impurities is a key quantity in understanding the physics of Kondo screening. Traditional numerical renormalization group (NRG) calculation of the impurity contribution χimp to susceptibility, defined originally by Wilson in a flat wide band, has been generalized before to structured conduction bands. The results brought about non-Fermi-liquid and diamagnetic Kondo behaviors in χimp, even when the bands are not gapped at the Fermi energy. Here, we use the full density-matrix (FDM) NRG to present high-quality data for the local susceptibility χ loc and to compare them with χimp obtained by the traditional NRG. Our results indicate that those exotic behaviors observed in χimp are unphysical. Instead, the low-energy excitations of the impurity in arbitrary bands only without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We also demonstrate that unlike the traditional NRG yielding χ loc less accurate than χimp, the FDM method allows a high-precision dynamical calculation of χ loc at much reduced computational cost, with an accuracy at least one order higher than χimp. Moreover, artifacts in the FDM algorithm to χimp, and origins of the spurious non-Fermi-liquid and diamagnetic features are clarified. Our work provides an efficient high-precision algorithm to calculate the spin susceptibility of impurity for arbitrary structured bands, while negating the applicability of Wilson's definition to such cases.

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Kondo effect in the presence of van Hove singularities: A numerical renormalization group study

Cited by 15 publications

References 49 publications

Quantum phase transitions into Kondo states in bilayer graphene

Quantum phase transitions into Kondo states in bilayer graphene

Spin-orbital and spin Kondo effects in parallel coupled quantum dots

Spin susceptibility of Anderson impurities in arbitrary conduction bands

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