Short-range antiferromagnetic correlations in Kondo insulators

Rappoport, Tatiana G.; Figueira, M. S.; Continentino, M. A.

doi:10.1016/s0375-9601(99)00837-3

Cited by 12 publications

(9 citation statements)

References 23 publications

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“…From the computational point of view the X-boson method is equivalent to the slave-boson technique, and the possibility of using it for all temperatures or chemical potentials µ makes it useful as the starting point to study several interesting problems: competition between Kondo effect and RKKY interaction in heavy fermion systems, [28][29][30] impurity bands in Kondo insulators, 31 non Fermi-liquid behavior in disordered systems, 32 and Kondo effect in quantum dots. 33,34 To give an example we have considered a Kondo insulator and calculated its specific heat: the slave boson method shows a discontinuity at T K , while it is continuous in the X-boson method.…”

Section: Discussionmentioning

confidence: 99%

“…(19)(20)(21)(22)(23)(24) and Eqs. (25)(26)(27)(28)(29)(30)). The obvious change √ D 0σ V → V , leaves an extra factor D 0σ in the G f f j′α′;jα (z n ) and G f f kσ (z n ), as well as a √ D 0σ in both G f c j;k,σ (z n ) and G f c kσ (z n ), and these factors are responsible for the correlation in this approximation, and lead to essential differences with the uncorrelated case.…”

Section: The Chain Approximation Green's Functionsmentioning

confidence: 99%

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X-boson cumulant approach to the periodic Anderson model

2002

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The Periodic Anderson Model (PAM) can be studied in the infinite U limit by employing the Hubbard X operators to project out the unwanted states. We have already studied this problem employing the cumulant expansion with the hybridization as perturbation, but the probability conservation of the local states (completeness) is not usually satisfied when partial expansions like the Chain Approximation (CHA) are employed. Here we treat the problem by a technique inspired in the mean field approximation of Coleman's slave-bosons method, and we obtain a description that avoids the unwanted phase transition that appears in the mean-field slave-boson method both when the chemical potential is greater than the localized level Ef at low temperatures (T) and for all parameters at intermediate T.Comment: Submited to Physical Review B 14 pages, 17 eps figures inserted in the tex

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Section: Discussionmentioning

confidence: 99%

Section: The Chain Approximation Green's Functionsmentioning

confidence: 99%

X-boson cumulant approach to the periodic Anderson model

2002

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“…AFM correlations have long been known to play a prominent role in metallic heavy fermion systems [37,38] , especially in the vicinity of quantum critical points. In Kondo insulators it has been argued, on the basis of a Kondo lattice model, that they can strongly renormalize the magnetic and transport gaps [39]. However, clear evidence for a Q dependence in the magnetic response measured by inelastic neutron scattering has been reported so far only for SmB 6 [40] and for CeNiSn [41], a material with pronounced Fermi surface anisotropy in which the gap is thought to exist only on a fraction of the Fermi surface.…”

Section: Discussionmentioning

confidence: 99%

Yb-Yb correlations and crystal field in the Kondo-insulator YbB 12

Alekseev

Mignot

Nemkovski

et al. 2002

Applied Physics A: Materials Science & Processing

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We have studied the effect of Lu substitution on the spin dynamics of the Kondo insulator YbB 12 to clarify the origin of the spin-gap response previously observed at low temperature in this material. Inelastic neutron spectra have been measured in Yb 1-x Lu x B 12 compounds for four Lu concentrations x = 0, 0.25, 0.90 and 1.0. The data indicate that the disruption of coherence on the Yb sublattice primarily affects the narrow peak structure occurring near 15-20 meV in pure YbB 12 , whereas the spin gap and the broad magnetic signal around 38 meV remain almost unaffected. It is inferred that the latter features reflect mainly local, singlesite processes, and may be reminiscent of the inelastic magnetic response reported for mixed-valence intermetallic compounds. On the other hand, the lower component at 15 meV is most likely due to dynamic short-range magnetic correlations. The crystal-field splitting in YbB 12 estimated from the Er 3+ transitions measured in a Yb 0.9 Er 0.1 B 12 sample, has the same order of magnitude as other relevant energy scales of the system and is thus likely to play a role in the form of the magnetic spectral response. Short title : Yb-Yb correlations and crystal-field effects in YbB 12 and its solid solutions

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“…Short-range AFM correlations are central to the physics of metallic HF systems [14], especially near quantum critical points, and there is evidence that they play a role in KI's as well [15,16]. It has been reported [17] that some metallic heavy rareearth RB 12 compounds order in complex, amplitudemodulated, incommensurate structures.…”

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Evidence for Short-Range Antiferromagnetic Fluctuations in Kondo-InsulatingYbB12

et al. 2005

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The spin dynamics of mixed-valence YbB12 has been studied by inelastic neutron scattering on a high-quality single crystal. In the Kondo-insulating regime realized at low temperature, the spectra exhibit a spin-gap structure with two sharp, dispersive, in-gap excitations athω ≈ 14.5 and ≈ 20 meV. The lower mode is shown to be associated with short-range correlations near the antiferromagnetic wave vector q0 = ( ). Its properties are in overall agreement with those expected for a "spin exciton" branch in an indirect hybridization gap semiconductor.Heavy-fermion compounds exhibit a whole spectrum of unconventional low-temperature behaviors, basically reflecting the existence of a very small energy scale, of the order of a few tens of kelvin, in the electron subsystem [1]. This energy scale is a hallmark of strong electron correlations and, in the metallic case, is associated with the Kondo temperature below which the heavy-quasiparticle Fermi liquid forms.In insulating compounds, on the other hand -so-called "Kondo insulators" (KI) or "mixed-valence semiconductors" (MVSC), such as CeNiSn, Ce 3 Bi 4 Pt 3 , SmB 6 , YbB 12 , or UPtSn -it corresponds to the opening of a very narrow, temperaturedependent, energy gap in the electron density of states [2]. The physical origin of this insulating state is still incompletely understood. It has been argued [3] that a number of aspects can be explained in terms of a oneelectron band picture, with a "hybridization gap" forming at low temperature in the electronic density of states at the Fermi energy [4]. However, there is growing evidence that strong electron-electron correlations are central to the emergence of the gap behavior, and that their effects cannot be reduced to a mere renormalization of quasiparticle states. The spin dynamics of these systems is also peculiar: in most examples studied to date, inelastic neutron scattering (INS) spectra typically exhibit a spin-gap response (∆ s ∼ 1 − 10 meV) at low temperature, which seems directly related to the KI state and disappears rapidly when a single-site fluctuation regime is recovered by heating [2]. Information on Q dependences has remained rather scarce, and to a large extent inconclusive, either because of complex anisotropy effects as in CeNiSn, or because measurements were carried out only on polycrystal samples. YbB 12 is a promising candidate for further investigations: it is an archetype KI compound [5] with a simple NaCl-type crystal structure (interpenetrating f cc sublattices of Yb ions and B 12 cuboctahedra), and previous inelastic neutron scattering (INS) experiments on powder [6,7,8] have indicated the presence of two narrow magnetic excitations near the spingap edge. Early single-crystal measurements [9] were interpreted in terms of a single dispersive low-energy mode with high intensity along [111], but the form of the Q dependence was not clearly established. In this Letter, we report a detailed investigation of the low-energy spin dynamics in YbB 12 showing that there indeed exist two distinct excitat...

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Short-range antiferromagnetic correlations in Kondo insulators

Cited by 12 publications

References 23 publications

X-boson cumulant approach to the periodic Anderson model

X-boson cumulant approach to the periodic Anderson model

Yb-Yb correlations and crystal field in the Kondo-insulator YbB 12

Evidence for Short-Range Antiferromagnetic Fluctuations in Kondo-InsulatingYbB12

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