Magnetic order in a Kondo lattice: A neutron scattering study of CeCu2Ge2

Knopp, G.; Loidl, A.; Knorr, K.; Pawlak, L.; Duczmal, Marek; Caspary, R.; Gottwick, U.; Spille, H.; Steglich, F.; Murani, A.P.

doi:10.1007/bf01313625

Cited by 105 publications

(75 citation statements)

References 29 publications

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“…At stoichiometries approaching x = 2 or pressures above 70 kbar the Kondo physics dominates dramatically with the emergence of superconductivity out of a heavy electron state [8,9]. A regime of superconductivity mediated by magnetic fluctuations may give over at even higher pressures to a regime mediated by valence fluctuations.In the pure CCG compound, the energy scales of the RKKY and the Kondo-type interactions are of the same order of magnitude [6] as demonstrated by the fact that the Kondo temperature only slightly exceeds T N . In the antiferromagnetic state the moments are partially Kondo compensated from 1.5 to 0.7 µ B .…”

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confidence: 81%

“…In the pure CCG compound, the energy scales of the RKKY and the Kondo-type interactions are of the same order of magnitude [6] as demonstrated by the fact that the Kondo temperature only slightly exceeds T N . In the antiferromagnetic state the moments are partially Kondo compensated from 1.5 to 0.7 µ B .…”

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confidence: 81%

“…Due to its smaller ionic size, Si substitution can be seen as a equivalent to increasing pressure. Pure CeCu 2 Ge 2 (CCG) is a Kondo-lattice system that exhibits an unusual temperature dependence of the resistivity caused by crystal field splitting and magnetic interactions at low temperatures [5][6][7]. An upturn of the resistivity around 25 K indicates the increasing effect upon cooling of scattering of the conduction electrons off the local moments.…”

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confidence: 99%

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Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu2Ge2

et al. 2012

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We present time-domain THz spectroscopy data of a thin film of the Kondo-lattice antiferromagnet CeCu2Ge2. The low frequency complex conductivity has been obtained down to temperatures below the onset of magnetic order. At low temperatures a narrow Drude-like peak forms, which is similar to ones found in other heavy fermion compounds that do not exhibit magnetic order. Using this data in conjunction with DC resistivity measurements, we obtain the frequency dependence of the scattering rate and effective mass through an extended Drude model analysis. The zero frequency limit of this analysis yields evidence for large mass renormalization even in the magnetic state, the scale of which agrees closely with that obtained from thermodynamic measurements.Kondo lattice systems in which localized f moments hybridize with extended conduction band electrons exhibit a rich variety of behavior. At high temperatures these systems behave as an ensemble of weakly interacting conduction electrons with modest masses and free fmoments. At low temperatures, the hybridization of local moments with the conduction electrons results in phenomena such as metallic states with charge carriers whose mass is hundreds of times the free electron mass (so called "heavy-fermion" behavior), superconductivity, and various interesting magnetic states [1][2][3]. Which physics is expressed at low temperature is determined by a delicate balance and competition between the Ruderman-KittelKasuya-Yosida (RKKY) type magnetic interaction and the hybridization of the 4f or 5f electrons with delocalized states [4]. Weak hybridization typically yields the RKKY-type interaction and magnetically ordered ground states. Strong hybridization, on the other hand, leads to the formation of fluctuating valence states, compensation of local moments, and heavy-electron metals. In the limiting case of very strong hybridization, the delocalized band electrons screen the localized f electrons, forming a singlet. Kondo lattice systems typically exhibit their heavy-electron effects below a temperature scale T * at which successive scattering from local moments starts to be in-phase and collective effects can appear.The competition between Kondo screening and the RKKY interaction is exhibited dramatically in the evolution of the electronic structure by Si substitution in the CeCu 2 Ge 2−x Si x Kondo-lattice series or by the application of pressure to the pure compound. Due to its smaller ionic size, Si substitution can be seen as a equivalent to increasing pressure. Pure CeCu 2 Ge 2 (CCG) is a Kondo-lattice system that exhibits an unusual temperature dependence of the resistivity caused by crystal field splitting and magnetic interactions at low temperatures [5][6][7]. An upturn of the resistivity around 25 K indicates the increasing effect upon cooling of scattering of the conduction electrons off the local moments. At approximately a temperature T * ∼ 6 K, the resistivity reaches a maximum, giving evidence for a low Kondo lattice temperature scale, before ordering antiferr...

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Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu2Ge2

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“…Below the Néel temperature of T N = 4.15 K, CeCu 2 Ge 2 orders in an incommensurate magnetic structure with a wave vector Q = (0.28 0.28 0.54) and an ordered moment of roughly 1 µ B . 45,46 With a Kondo temperature similar to the ordering temperature 47 and a low Sommerfeld coefficient of the specific heat 48 (see Table I) CeCu 2 Ge 2 is believed to be a local-moment antiferromagnet. However, theoretical calculations indicate that a full local-moment picture cannot account for the observed incommensurate propagation vector, but a certain degree of itineracy is needed.…”

Section: Superconductivity Near First Order Transitionsmentioning

confidence: 99%

Superconductivity in Ce- and U-Based “122” Heavy-Fermion Compounds

et al. 2012

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“…11(a). It is isostructural to CeCu 2 Si 2 -the first discovered heavy fermion superconductor [40] and CeCu 2 Ge 2 , an incommensurate antiferromagnet [41], that becomes superconducting above 70 kbar in a pressure cell [42].…”

Section: Cepd2si2 and Cerh2si2mentioning

confidence: 99%

Kramers degeneracy in a magnetic field and Zeeman spin-orbit coupling in antiferromagnetic conductors

Ramazashvili

2009

Phys. Rev. B

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In this article, I analyze the symmetries and degeneracies of electron eigenstates in a commensurate collinear antiferromagnet. In a magnetic field transverse to the staggered magnetization, a hidden anti-unitary symmetry protects double degeneracy of the Bloch eigenstates at a special set of momenta. In addition to this 'Kramers degeneracy' subset, the manifold of momenta, labeling the doubly degenerate Bloch states in the Brillouin zone, may also contain an 'accidental degeneracy' subset, that is not protected by symmetry and that may change its shape under perturbation. These degeneracies give rise to a substantial momentum dependence of the transverse g-factor in the Zeeman coupling, turning the latter into a spin-orbit interaction.I discuss a number of materials, where Zeeman spin-orbit coupling is likely to be present, and outline the simplest properties and experimental consequences of this interaction, that may be relevant to systems from chromium to borocarbides, cuprates, hexaborides, iron pnictides, as well as organic and heavy fermion conductors.

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Magnetic order in a Kondo lattice: A neutron scattering study of CeCu2Ge2

Cited by 105 publications

References 29 publications

Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu2Ge2

Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu2Ge2

Superconductivity in Ce- and U-Based “122” Heavy-Fermion Compounds

Kramers degeneracy in a magnetic field and Zeeman spin-orbit coupling in antiferromagnetic conductors

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