Kondo effect in flux phases

Cassanello, Carlos; Fradkin, Eduardo

doi:10.1103/physrevb.53.15079

Cited by 95 publications

(181 citation statements)

References 21 publications

(50 reference statements)

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“…Large-N methods have been applied 3,4 to models describing magnetic impurities in unconventional superconductors, in which the power-law variation of ρ(ǫ) is restricted to a region |ǫ| < ∆. These studies, which may be directly relevant for Ni-doping experiments 20 on YBa 2 Cu 3 O 7−δ , have yielded results in general agreement with Ref.…”

Section: Introductionsupporting

confidence: 71%

“…10, which shows the impurity susceptibility and specific heat for a linear scattering rate. As noted above, the case r = 1 is of particular interest because it may describe a magnetic impurity in a d-wave superconductor 3,4 and in flux phases of two-dimensional electrons.…”

Section: ) If the Deviation From Unity Of The Ratio R W /R (0)mentioning

confidence: 99%

“…In the specific case r = 1, these power laws acquire logarithmic corrections. 4 For r ≤ 1 or N = 2, any finite impurity concentration produces a small infilling of the pseudogap which drives J c to zero. 3 Numerical renormalization-group (RG) calculations 5,7 for the case N = 2 have revealed a number of additional features.…”

Section: Introductionmentioning

confidence: 99%

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Renormalization-group study of Anderson and Kondo impurities in gapless Fermi systems

1998

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Thermodynamic properties are presented for four magnetic impurity models describing delocalized fermions scattering from a localized orbital at an energy-dependent rate Γ(ǫ) which vanishes precisely at the Fermi level, ǫ = 0. Specifically, it is assumed that for small |ǫ|, Γ(ǫ) ∝ |ǫ| r with r > 0. The cases r = 1 and r = 2 describe dilute magnetic impurities in unconventional (d-and p-wave) superconductors, "flux phases" of the two-dimensional electron gas, and certain zero-gap semiconductors. For the nondegenerate Anderson model, the main effects of the depression of the low-energy scattering rate are the suppression of mixed valence in favor of local-moment behavior, and a marked reduction in the exchange coupling on entry to the local-moment regime, with a consequent narrowing of the range of parameters within which the impurity spin becomes Kondo-screened. The precise relationship between the Anderson model and the exactly screened Kondo model with power-law exchange is examined. The intermediate-coupling fixed point identified in the latter model by Withoff and Fradkin (WF) is shown to have clear signatures both in the thermodynamic properties and in the local magnetic response of the impurity. The underscreened, impurity-spin-one Kondo model and the overscreened, two-channel Kondo model both exhibit a conditionally stable intermediatecoupling fixed point in addition to unstable fixed points of the WF type. In all four models, the presence or absence of particle-hole symmetry plays a crucial role in determining the physics both at strong coupling and in the vicinity of the WF transition. These results are obtained using an extension of Wilson's numerical renormalization-group technique to treat energy-dependent scattering. The strong-and weak-coupling fixed points of each model are identified and their stability is analyzed. Algebraic expressions are derived for the fixed-point thermodynamic properties, and for low-temperature corrections about the stable fixed points. Numerical data are presented confirming the algebraic results, identifying and characterizing intermediate-coupling (non-Fermi-liquid) fixed points, and exploring temperature-driven crossovers between different physical regimes.

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Section: Introductionsupporting

confidence: 71%

Section: ) If the Deviation From Unity Of The Ratio R W /R (0)mentioning

confidence: 99%

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Renormalization-group study of Anderson and Kondo impurities in gapless Fermi systems

1998

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“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] More recently, impurity physics has been studied in the context of strongly interacting systems. Numerous examples include 21 an impurity in systems with vanishing density of states 22,23 high temperature superconductors, 24 and quantum magnets. [25][26][27][28][29][30] Quantum magnets are particularly versatile as a host system, having a large number of possible ground states with different low energy excitations.…”

Section: Introductionmentioning

confidence: 99%

Overscreened Kondo fixed point inS=1spin liquid

2013

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We propose a possible realization of the overscreened Kondo impurity problem by a magnetic s = 1/2 impurity embedded in a two-dimensional S = 1 U (1) spin liquid with a Fermi surface. This problem contains an interesting interplay between non-Fermi-liquid behavior induced by a U (1) gauge field coupled to fermions and a non-Fermi-liquid fixed point in the overscreened Kondo problem. Using a large-N expansion together with an expansion in the dynamical exponent of the gauge field, we find that the coupling to the gauge field leads to weak but observable changes in the physical properties of the system at the overscreened Kondo fixed point. We discuss the extrapolation of this result to a physical case and argue that the realization of overscreened Kondo physics could lead to observations of effects due to gauge fields.

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“…Diverse theoretical techniques have been employed to study Kondo or Anderson models in a superconducting environment [1][2][3][4][5][6][7][8][9]. Most of these studies effectively neglect the presence of superconducting (sc) fluctuations in the host, i.e., they use the local fermionic density of states (DOS) as the only input quantity characterizing the environment of the Kondo impurity.…”

mentioning

confidence: 99%

Kondo screening in unconventional superconductors: The role of anomalous propagators

Fritz

Vojta

2005

Phys. Rev. B

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The Kondo effect in superconductors is frequently investigated using the local quasiparticle density of states as sole bath characteristics, i.e., the presence of anomalous propagators is ignored. Here we point out that this treatment is exact for a number of situations, including point-like impurities in dwave superconductors. We comment on recent investigations [M. M. Koga, J. Phys. Soc. Jpn. 70, 2860 (2001) and Phys. Rev. B 65, 024508 (2002)] which reached different conclusions: while their numerical results are likely correct, their interpretation in terms of two-channel Kondo physics and an "orbital effect of Cooper pairs" is incorrect.PACS numbers: 75.20.Hr, The physics of quantum impurity moments in superconductors, associated with the Kondo effect, has been subject of numerous investigations in recent years. Diverse theoretical techniques have been employed to study Kondo or Anderson models in a superconducting environment [1][2][3][4][5][6][7][8][9]. Most of these studies effectively neglect the presence of superconducting (sc) fluctuations in the host, i.e., they use the local fermionic density of states (DOS) as the only input quantity characterizing the environment of the Kondo impurity. For s-wave superconductors it has been shown [1] that this approximation is not justified: here the properties of a Kondo impurity are different from the ones of an impurity embedded in a non-superconducting system with the same DOS. More precisely, the superconducting bath turns out to be equivalent to a non-superconducting bath with additional particle-hole (p-h) asymmetry [1]. As a result, for a p-h symmetric conduction band a screened singlet state is realized at large Kondo coupling, in contrast to the non-sc case with a hard gap in the local DOS [11]. This difference can be understood as caused by the anomalous bath propagators.In this Brief Report, we address the role of anomalous propagators in unconventional superconductors. We argue below that neglecting sc propagators is exact in many, potentially experimentally relevant, cases, e.g., for point-like impurities in d-wave and unitary p-wave superconductors. In these situations, the dynamics of the impurity degrees of freedom can be calculated using the normal bath propagators only. We also comment on recent papers by Matsumoto and Koga who argued in favor of a non-trivial "orbital effect of Cooper pairs" for pointlike impurities in both p + ip and d + id superconductors [7,8]. While we believe that their numerical results are correct, we point out that such an orbital effect does not exist: in their situation the impurity properties are exclusively determined by the local DOS.We start from the action of an Anderson impurity in a general interacting host.where β = 1/T is the inverse temperature, c are the conduction electrons with dispersion ǫ k on a regular lattice with N sites, S int are the interactions within the conduction band, and S loc describes the f electron impurity orbital with on-site energy and repulsion. The sum {i} runs over a set of lattic...

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Kondo effect in flux phases

Cited by 95 publications

References 21 publications

Renormalization-group study of Anderson and Kondo impurities in gapless Fermi systems

Renormalization-group study of Anderson and Kondo impurities in gapless Fermi systems

Overscreened Kondo fixed point inS=1spin liquid

Kondo screening in unconventional superconductors: The role of anomalous propagators

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