Cu NMR and NQR study of impurity-doped YBa2Cu3O7

Ishida, K.; Kitaoka, Y.; Ogata, Nobuhito; Kamino, T.; Cooper, J. R.

doi:10.1016/0921-4526(93)90772-x

Cited by 9 publications

(7 citation statements)

References 3 publications

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“…Here Λ parametrizes the discretization: numerical calculations are typically performed with Λ = 2-3, while the continuum is recovered in the limit Λ → 20) and…”

Section: Discretization Of the Conduction Bandmentioning

confidence: 99%

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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“…Here Λ parametrizes the discretization: numerical calculations are typically performed with Λ = 2-3, while the continuum is recovered in the limit Λ → 20) and…”

Section: Discretization Of the Conduction Bandmentioning

confidence: 99%

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

1998

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“…41,42 However, a recent NQR result under P at xϭ0.02 reveals that the AFM order is suppressed and the HF superconductivity with the line-node gap is recovered by applying pressures. 40 This result apparently excludes such the impurity effect as a cause for the enhancement of 1/T 1 below T c .…”

Section: B Nuclear Spin-lattice Relaxation Rate 1õtmentioning

confidence: 99%

Exotic magnetism and superconductivity in Ge-substitutedCeCu2Si2:A Cu NQR study

et al. 2002

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We report Cu NQR results on Ge-doped heavy-fermion superconductors CeCu 2 (Si 1Ϫx Ge x ) 2 (0Ͻxр0.2) and compare with previous results on Ce 0.99 Cu 2.02 Si 2 (xϭ0). Once only 1% Ge is substituted for Si to expand the lattice, an antiferromagnetic ͑AFM͒ order sets in at T N ϳ0.7 K, followed by the onset of superconductivity at T c ϭ0.5 K. The sudden emergence of AFM order due to the slight Ge doping reinforces that an exotic magnetic phase at xϭ0 is in fact a marginal AFM state where slowly fluctuating AFM waves propagate over a long distance. The appearance of internal fields throughout the sample that is deduced from the NQR spectral shape below T N , excludes the presence of phase segregation between the superconducting ͑SC͒ and the AFM phases in the coexistent state below T c . The 1/T 1 result does not show significant reduction below T c , followed by a T 1 Tϭconst behavior. This indicates that the SC phase is in a gapless regime, dominated by magnetic excitations due to the coexistence of AFM and SC phase. As Ge content increases, T N is progressively increased, while T c is steeply decreased. As a result of the suppression of the slowly fluctuating AFM waves in the samples with more than xϭ0.06, their magnetic properties above T N progressively change to those in a localized regime as observed in CeCu 2 Ge 2 . The exotic interplay between magnetism and superconductivity in 0рxϽ0.06 is discussed in the context of a SO͑5͒ theory that unifies superconductivity and antiferromagnetism.

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“…Perhaps the strongest assumptions are the correctness and applicability of the standard theory of disordered superconductors, about which more will be said below. The experiments fall into two classes: impurity doping, 65,168,169 usually with Zn or Ni, and planar oxygen displacement by electron irradiation. 170,171 ,87…”

Section: Effects Of Impuritiesmentioning

confidence: 99%

Experimental Constraints on the Pairing State of the Cuprate Superconductors: An Emerging Consensus

Annett

Goldenfeld

Leggett

1996

Physical Properties of High Temperature Superconductors V

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We present a critical discussion of recent experimental probes of the pairing state of the high temperature superconductors, focusing primarily, but not exclusively, on YBa 2 Cu 3 O 7−δ , where the best data currently exist. Penetration depth measurements near T c give no indication of an extra transition, indicating that the pairing state is a one-dimensional representation of the crystal symmetry. Penetration depth measurements at low temperatures provide strong evidence for a change in sign of the gap function over the Fermi surface. Quantum mechanical phase interference experiments generally confirm this and in addition show that the nodal positions are consistent with a d x 2 −y 2 pairing state. This pairing state is consistent with photoemission measurements of the gap function, Raman scattering, the effect on T c of impurities, and many other data (reviewed by two of us previously) which indicate the presence of low lying excitations in the superconducting state. We also discuss evidence that apparently does not fit in with a d x 2 −y 2 pairing state, and we describe possible alternative scenarios.

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Cu NMR and NQR study of impurity-doped YBa2Cu3O7

Cited by 9 publications

References 3 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

Exotic magnetism and superconductivity in Ge-substitutedCeCu2Si2:A Cu NQR study

Experimental Constraints on the Pairing State of the Cuprate Superconductors: An Emerging Consensus

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