Universal Scaling in the Dynamical Conductivity of Heavy Fermion Ce and Yb Compounds

Okamura, Hidekazu; Watanabe, Tatsuya; Matsunami, Masaharu; Nishihara, Tomohisa; Tsujii, Naohito; Ebihara, Takao; Sugawara, Hitoshi; Sato, Hideyuki; Ōnuki, Yoshichika; Isikawa, Yosikazu; Takabatake, Toshiro; Nanba, Tetsuya

doi:10.1143/jpsj.76.023703

Cited by 51 publications

(76 citation statements)

References 49 publications

(67 reference statements)

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“…For T ≤ T 0 , the zero-field anomalies in χ(T ) and C V (T ) yield an enhanced effective mass 27 of the order of 1/T 0 and the neutron scattering data 29,30 show a narrow peak at about 30 meV, which is due to a hybridization gap. However, if we plot the low-temperature transport coefficients on a reduced temperature scale T/T K they appear to be strongly enhanced with respect to the predictions of the single impurity Anderson model with Kondo scale T K ≃ 500 K. Neither the A coefficient of the resistivity nor the slope of the thermopower can be explained by the single impurity c calculations that would capture the main features of the high-temperature data and give T K ≃ 500 K. Optical conductivity at 7 K shows a narrow Drude-like response that is often found in heavy fermion systems 32,33 and another mid-infrared peak (MIR) that can be associated with the hybridization gap. The optical spectra do not change appreciably for 7 K ≤T≤ 40 K, as expected of a system with the characteristic energy scale T 0 ≃ 50 K. However, the Drude peak broadens and the MIR peak vanishes at higher temperatures.…”

Section: The T0 ≪ Tk Casementioning

confidence: 84%

Multiple temperature scales of the periodic Anderson model: Slave boson approach

Burdin

Zlatič

2009

Phys. Rev. B

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The thermodynamic and transport properties of intermetallic compounds with Ce, Eu, and Yb ions are discussed using the periodic Anderson model with an infinite correlation between f electrons. At high temperatures, these systems exhibit typical features that can be understood in terms of a single impurity Anderson or Kondo model with Kondo scale TK . At low temperatures, the normal state is governed by the Fermi liquid (FL) laws with characteristic energy scale T0. The slave boson solution of the periodic model shows that T0 and TK depend not only on the degeneracy and the splitting of the f states, the number of c and f electrons, and their coupling, but also on the shape of the conduction electrons density of states (c DOS) in the vicinity of the chemical potential.We show that the details of the band structure determine the ratio T0/TK and that the crossover between the high-and low-temperature regimes in ordered compounds is system-dependent. A sharp peak in the c DOS yields T0 ≪TK and explains the 'slow crossover' observed in YbAl3 or YbMgCu4. A minimum in the c DOS yields T0 ≫TK , which leads to the abrupt transition between the high-and low-temperature regimes in YbInCu4. In the case of CeCu2Ge2 and CeCu2Si2, where T0 ≃ TK , the slave boson solution explains the pressure experiments which reveal sharp peaks in the T 2 coefficient of the electrical resistance, A = ρ(T )/T 2 , and the residual resistance. These peaks are due to the change in the degeneracy of the f states induced by the applied pressure.The FL laws explain also the correlation between the specific heat coefficient γ = CV /T and the slope of the thermopower α(T )/T , or between γ and the A coefficient of the resistivity. For N -fold degenerate model, the FL laws explain the deviations from universal value of the Kadowaki-Woods ratio, RKW = A/γ 2 , and the ratio q = lim {T →0} α/γT . The renormalization of transport coefficients can invalidate the Wiedemann-Franz law and lead to an enhancement of the thermoelectric figure-ofmerit. We show that the low-temperature response of the periodic Anderson model can be enhanced (or reduced) with respect to the predictions based on the single-impurity models that give the same high-temperature behavior.

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Section: The T0 ≪ Tk Casementioning

confidence: 84%

Multiple temperature scales of the periodic Anderson model: Slave boson approach

Burdin

Zlatič

2009

Phys. Rev. B

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“…They suggested that the bandwidth W of a Ce (Yb) compound could be regarded as inversely proportional to specific heat coefficient γ of the non-magnetic, isostructural La (Lu) compound (denoted as γ 0 ). T K is expressed in terms of the electronic specific heat coefficient γ as 28,48…”

Section: Universal Scaling In Ce-and Yb-based Compoundsmentioning

confidence: 99%

Infrared properties of heavy fermions: evolution from weak to strong hybridizations

Chen¹,

Wang²

2016

Rep. Prog. Phys.

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In this article, we review the charge excitations of heavy fermion compounds probed by infrared spectroscopy. The article is not meant to be a comprehensive survey of experimental investigations. Rather it focuses on the dependence of charge excitations on the hybridization strength. In this context, the infrared properties of the Ce m M n In 3m+2n family are discussed in detail since the hybridization strengths differ dramatically in different members despite their similar lattice structures. Investigations on some mixed valent compounds are also presented aiming to elucidate the generic trend on the evolution. In particular, we address the scaling between hybridization energy gap ∆ dir and the hybridization strengthṼ(∝ √ WT K ) in a wide range of heavy fermions compounds which demonstrates that the periodic Anderson model can generally and quantitatively describe the low-energy charge excitations.

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“…The hybridization gap in the infrared is another well-studied characteristic of heavy-fermion optics. 12,13 It is usually attributed to excitations over the gap in the density of states that develops due to the hybridization, 14 but there are also recent calculations that describe such a gap structure in the conductivity as a band-structure effect. 15,16 In the present study we concentrate on frequencies that are much lower than those typically assumed for the hybridization gap.…”

Section: Introductionmentioning

confidence: 99%

Terahertz conductivity of the heavy-fermion compound UNi2Al3

et al. 2011

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We have studied the optical properties of the heavy-fermion compound UNi2Al3 at frequencies between 100 GHz and 1 THz (3 cm^-1 and 35 cm^-1), temperatures between 2 K and 300 K, and magnetic fields up to 7 T. From the measured transmission and phaseshift of radiation passing through a thin film of UNi2Al3, we have directly determined the frequency dependence of the real and imaginary parts of the optical conductivity (or permittivity, respectively). At low temperatures the anisotropy of the optical conductivity along the a- and c-axes is about 1.5. The frequency dependence of the real part of the optical conductivity shows a maximum at low temperatures, around 3 cm^-1 for the a-axis and around 4.5 cm^-1 for the c-axis. This feature is visible already at 30 K, much higher than the Neel temperature of 4.6 K, and it does not depend on external magnetic fields as high as 7 T. We conclude that this feature is independent of the antiferromagnetic order for UNi2Al3, and this might also be the case for UPd2Al3 and UPt3, where a similar maximum in the optical conductivity was observed previously.Comment: 7 pages, 9 figure

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Universal Scaling in the Dynamical Conductivity of Heavy Fermion Ce and Yb Compounds

Cited by 51 publications

References 49 publications

Multiple temperature scales of the periodic Anderson model: Slave boson approach

Multiple temperature scales of the periodic Anderson model: Slave boson approach

Infrared properties of heavy fermions: evolution from weak to strong hybridizations

Terahertz conductivity of the heavy-fermion compound UNi2Al3

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