The electrodynamic response of heavy-electron materials with magnetic phase transitions

Degiorgi, L.; Thieme, St.; Ott, H. R.; Dressel, Martin; Grüner, G.; Dalichaouch, Y.; Maple, M. B.; Fisk, Z.; Geibel, C.; Steglich, F.

doi:10.1007/s002570050300

Cited by 48 publications

(58 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The combination of the two effects gives a Drude peak that is narrowing and increasing in height but also losing some spectral weight to hybridization. This behaviour, namely the suppression of the background conductivity at higher frequencies and the sharpening of the Drude peak, has been observed in other heavy fermion compounds, such as YbFe [18], and UCu 5 and UPd 2 Al 3 [6]. Figure 3 shows the partial spectral weight, N ef f (Ω, T ) − N ef f (Ω, 100), where N ef f (Ω, T ) = Ω 0 σ(ω, T )dω and where we have subtracted the partial spectral weight at 100 K over a wider range of frequencies.…”

Section: Hybridization Regionmentioning

confidence: 93%

“…Band structure calculations [46,47] have yielded a picture of the Fermi surface with strong nesting in the pressure-induced anti-ferromagnetic state, and quantum oscillation measurements [37] demonstrate that there is no significant Fermi surface restructuring between HO and LM-AFM, which implies that the Fermi surface calculated for the latter state applies equally well to the former. Incommensurate nesting will lead to the formation of a spin-density wave gap at F and will be accompanied by a sharp absorption feature in the optical data [6,48], while a commensurate antiferromagnetic order of the localized moments would not be visible in optical measurements because it would not lead to a gap in the excitation spectrum at F .…”

Section: The Hidden Order Statementioning

confidence: 99%

“…The spectral weight lost in the gap was transferred to frequencies just above the gap, typical of a density wave transition. Subsequent optical work has centred around investigations of the effects of doping on the hidden order [5,6], of the effect of hybridization on the electrodynamics [7][8][9][10] and the anisotropy of the hidden order parameter [11]. The superconducting state occurs below the temperatures available in typical optical experiments; likewise, the large moment antiferromagnet state (LM-AFM) induced by hydrostatic pressure has not yet been investigated optically.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Optical study of hybridization and hidden order in URu₂Si₂

Hall

Timusk

2014

Philosophical Magazine

View full text Add to dashboard Cite

We summarize existing optical data of URu 2 Si 2 to clarify the nature of the hidden order transition in this heavy fermion metal. Hybridization develops between 50 K and 17.5 K, and a coherent Drude peak emerges which mirrors the changes in the dc resistivity. The Drude weight indicates that there is little change in the effective mass of these carriers in this temperature range. In addition, there is a flat background conductivity that develops a partial hybridization gap at 10 meV as the temperature is lowered, shifting spectral weight to higher frequencies above 300 meV. Below 30 K the carriers become increasingly coherent and Fermi-liquid-like as the hidden order transition is approached. The hidden order state in URu 2 Si 2 is characterized by multiple anisotropic gaps. The gap parameter ∆a = 3.2 meV in the ab-plane. In the c-direction, there are two distinct gaps with magnitudes of ∆ c1 = 2.7 meV and ∆ c2 = 1.8 meV. These observations are in good agreement with other spectroscopic measurements. Overall, the spectrum can be fit by a Dynes-type density of states model to extract values of the hidden order gap. The transfer of spectral weight strongly resembles what one sees in density wave transitions.

show abstract

Section: Hybridization Regionmentioning

confidence: 93%

Section: The Hidden Order Statementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Optical study of hybridization and hidden order in URu₂Si₂

Hall

Timusk

2014

Philosophical Magazine

View full text Add to dashboard Cite

show abstract

“…44 For Kramers-Kronig analysis, we took a Hagen-Rubens extrapolation below our lowest measured frequency. Above 40 000 cm −1 , we utilized the data by Degiorgi et al 45 up to 100 000 cm −1 (12 eV), followed by a ω −4 free electron termination. Figure 6 shows the optical conductivity around each phonon for both polarizations.…”

Section: Optical Conductivity Of Phonons a Methodsmentioning

confidence: 99%

Lattice dynamics of the heavy-fermion compoundURu2Si2

et al. 2015

View full text Add to dashboard Cite

We report a comprehensive investigation of the lattice dynamics of URu2Si2 as a function of temperature using Raman scattering, optical conductivity and inelastic neutron scattering measurements as well as theoretical ab initio calculations. The main effects on the optical phonon modes are related to Kondo physics. The B1g (Γ3 symmetry) phonon mode slightly softens below ∼100 K, in connection with the previously reported softening of the elastic constant, C11 − C12, of the same symmetry, both observations suggesting a B1g symmetry-breaking instability in the Kondo regime. Through optical conductivity, we detect clear signatures of strong electron-phonon coupling, with temperature dependent spectral weight and Fano line shape of some phonon modes. Surprisingly, the line shapes of two phonon modes, Eu(1) and A2u(2), show opposite temperature dependencies. The A2u(2) mode loses its Fano shape below 150 K, whereas the Eu(1) mode acquires it below 100 K, in the Kondo cross-over regime. This may point out to momentum-dependent Kondo physics. By inelastic neutron scattering measurements, we have drawn the full dispersion of the phonon modes between 300 K and 2 K. No remarkable temperature dependence has been obtained including through the hidden order transition. Ab initio calculations with the spin-orbit coupling are in good agreement with the data except for a few low energy branches with propagation in the (a,b) plane.

show abstract

“…At low frequency, below 4 meV, a Drude response was assumed where we used the measured dc resistivity to determine the amplitude of the Drude peak and the absorption at our lowest measured infrared frequency to determine the width. At high frequency, beyond 7 eV, we used the results of Degiorgi et al (33).…”

mentioning

confidence: 99%

Optical spectroscopy shows that the normal state of URu ₂ Si ₂ is an anomalous Fermi liquid

Nagel

Uleksin

Rõõm

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau-Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a LandauFermi liquid, the ratio of the two terms, b, has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal URu 2 Si 2 , instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to URu 2 Si 2 . Fermi liquid-like states with b ≠ 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized.hidden order | resistance | infrared conductivity | resonant scattering A mong the heavy Fermion metals, URu 2 Si 2 is one of the most interesting: it displays, in succession, no fewer than four different behaviors. As is shown in Fig. 1, where the electrical resistivity is plotted as a function of temperature, at 300 K the material is a very bad metal in which the conduction electrons are incoherently scattered by localized uranium f electrons. Below T K ∼ 75 K, the resistivity drops and the material resembles a typical heavy Fermion metal (1-3). At T 0 = 17.5 K the "hiddenorder" phase transition gaps a substantial portion of the Fermi surface but the nature of the order parameter is not known. A number of exotic models for the ordered state have been proposed (4-7), but there is no definitive experimental evidence to support them. Finally, at 1.5 K URu 2 Si 2 becomes an unconventional superconductor. The electronic structure, as shown by both angle-resolved photoemission experiments (8) and bandstructure calculations (9) is complicated, with several bands crossing the Fermi surface. To investigate the nature of the hidden-order state we focus on the normal state just above the transition. This approach has been used in the high-temperature superconductors where the normal state shows evidence of discrete frequency magnetic excitations that appear to play the role that phonons play in normal superconductors (10). The early optical experiments of Bonn et al. (11) showed that URu 2 Si 2 at 20 K, above the hidden order transition, has an infrared spectrum consisting ...

show abstract

The electrodynamic response of heavy-electron materials with magnetic phase transitions

Abstract: Abstract. We have investigated the electrodynamic

Cited by 48 publications

References 55 publications

Optical study of hybridization and hidden order in URu₂Si₂

Optical study of hybridization and hidden order in URu₂Si₂

Lattice dynamics of the heavy-fermion compoundURu2Si2

Optical spectroscopy shows that the normal state of URu ₂ Si ₂ is an anomalous Fermi liquid

Contact Info

Product

Resources

About

The electrodynamic response of heavy-electron materials with magnetic phase transitions

Abstract: Abstract. We have investigated the electrodynamic

Cited by 48 publications

References 55 publications

Optical study of hybridization and hidden order in URu2Si2

Optical study of hybridization and hidden order in URu2Si2

Lattice dynamics of the heavy-fermion compoundURu2Si2

Optical spectroscopy shows that the normal state of URu 2 Si 2 is an anomalous Fermi liquid

Contact Info

Product

Resources

About

Optical study of hybridization and hidden order in URu₂Si₂

Optical study of hybridization and hidden order in URu₂Si₂

Optical spectroscopy shows that the normal state of URu ₂ Si ₂ is an anomalous Fermi liquid