Growth and properties of heavy fermion CeCu2Ge2 and CeFe2Ge2 thin films

Li, Yize Stephanie; Zheng, Min; Mulcahy, Brian; Greene, L. H.; Eckstein, J. N.

doi:10.1063/1.3610975

Applied Physics Letters

2011

DOI: 10.1063/1.3610975

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Growth and properties of heavy fermion CeCu2Ge2 and CeFe2Ge2 thin films

Yize Stephanie Li

Min Zheng

Brian Mulcahy

et al.

Abstract: Epitaxial films of heavy fermion CeCu2Ge2 and CeFe2Ge2 are grown on DyScO3 and MgO substrates using molecular beam epitaxy. The growth begins via island nucleation leading to a granular morphology. The grains grow flat with c-axis orientation after nucleating, as indicated by in-situ reflection high energy electron diffraction (RHEED) and ex-situ analysis including atomic force microscopy (AFM) and x-ray diffraction (XRD). These single phase films show similar temperature dependent transport to single crystals… Show more

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Cited by 7 publications

(12 citation statements)

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“…1 we show DC resistivity data as a function of temperature of the film studied in this work. As demonstrated previously, transport measurements of the films find quantitative agreement with the temperature scales found in bulk single crystals [7]. A number of prominent features can be noted.…”

supporting

confidence: 67%

“…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.…”

mentioning

confidence: 99%

“…In-situ RHEED and ex-situ AFM and XRD were used post-growth to characterize the films. Details of the growth have been reported elsewhere [7].…”

mentioning

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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confidence: 67%

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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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“…4(b). The overall scale of the mass is set by the measured plasma frequency and although it is possible that we have parameterized it inaccurately, the present value of the low temperature renormalized mass is consistent with heat capacity measurements and materials with similar specific heat coefficients [9,23].…”

mentioning

confidence: 68%

“…In this expression n is the index of refraction of the substrate, ∆L is a correction factor that accounts for thickness differences between the reference substrate and the sample substrate, d is the film thickness, and Z 0 is the impedance of free space (377 Ω). The films studied in this work were grown by molecular beam epitaxy to a thickness of 524Å using flux-matched codeposition on MgO substrates [23].…”

mentioning

confidence: 99%

Anomalous frequency and temperature-dependent scattering and Hund's coupling in the almost quantum critical heavy-fermion systemCeFe2Ge2

Bosse

Pan

et al. 2016

Phys. Rev. B

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We present THz range optical conductivity data of a thin film of the near quantum critical heavy fermion compound CeFe2Ge2. Our complex conductivity measurements find a deviation from conventional Drude-like transport in a temperature range previously reported to exhibit unconventional behavior. We calculate the frequency dependent effective mass and scattering rate using an extended Drude model analysis. We find the inelastic scattering rate can be described by a temperature dependent power-law ω n(T ) where n(T ) approaches ∼ 1.0 ± 0.2 at 1.5 K. This is compared to the ρ ∼ T 1.5 behavior claimed in dc resistivity data and the ρ ∼ T 2 expected from Fermi-liquid theory. In addition to a low temperature mass renormalization, we find an anomalous mass renormalization that persists to high temperature. We attribute this to a Hund's coupling in the Fe states in a manner similar to that recently proposed in the ferro-pnictides. CeFe2Ge2 appears to be a very interesting system where one may study the interplay between the usual 4f lattice Kondo effect and this Hund's enhanced Kondo effect in the 3d states.

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Microwave spectroscopy on heavy‐fermion systems: Probing the dynamics of charges and magnetic moments

Scheffler

Schlegel

Clauss

et al. 2013

Physica Status Solidi (b)

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Investigating solids with light gives direct access to charge dynamics, electronic and magnetic excitations. For heavy fermions, one has to adjust the frequency of the probing light to the small characteristic energy scales, leading to spectroscopy with microwaves. We review general concepts of the frequency-dependent conductivity of heavy fermions, including the slow Drude relaxation and the transition to a superconducting state, which we also demonstrate with experimental data taken on UPd 2 Al 3 . We discuss the optical response of a Fermi liquid and how it might be observed in heavy fermions. Microwave studies with focus on quantum criticality in heavy fermions concern the charge response, but also the magnetic moments can be addressed via electron spin resonance (ESR). We discuss the case of YbRh 2 Si 2 , the open questions concerning ESR of heavy fermions, and how these might be addressed in the future. This includes an overview of the presently available experimental techniques for microwave studies on heavy fermions, with a focus on broadband studies using the Corbino approach and on planar superconducting resonators.

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Growth and properties of heavy fermion CeCu2Ge2 and CeFe2Ge2 thin films

Cited by 7 publications

References 15 publications

Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu2Ge2

Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu2Ge2

Anomalous frequency and temperature-dependent scattering and Hund's coupling in the almost quantum critical heavy-fermion systemCeFe2Ge2

Microwave spectroscopy on heavy‐fermion systems: Probing the dynamics of charges and magnetic moments

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