Emergent Critical Charge Fluctuations at the Kondo Breakdown of Heavy Fermions

Komijani, Yashar; Coleman, Piers

doi:10.1103/physrevlett.122.217001

Cited by 49 publications

(40 citation statements)

References 53 publications

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“…Near a Kondo-breakdown QCP, when the low-energy Fermi liquid scale T * vanishes, dynamical response quantities should obey ω/T scaling of the form σ (ω, T ) ∝ T −α f (hω/k B T ) with a universal scaling function f (x). This was theoretically expected [43,44] and experimentally found not only in CeCu 5.9 Au 0.1 for the dynamic magnetic response [31], but also more recently in YbRh 2 Si 2 for the optical conductivity [37]. Note that T * is to be distinguished from the Kondo lattice temperature T * K characterizing the onset of Kondo spin-screening and heavy quasiparticle formation.…”

Section: Resultssupporting

confidence: 64%

Terahertz conductivity of heavy-fermion systems from time-resolved spectroscopy

Yang

Pal

Zamani³

et al. 2020

Phys. Rev. Research

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The Drude model describes the free-electron conduction in simple metals, governed by the freedom that the mobile electrons have within the material. In strongly correlated systems, however, a significant deviation of the optical conductivity from the simple metallic Drude behavior is observed. Here, we investigate the optical conductivity of the heavy-fermion system CeCu 6−x Au x , using time-resolved, phase-sensitive terahertz spectroscopy. The terahertz electric field creates two types of excitations in heavy-fermion materials: First, the intraband excitations that leave the heavy quasiparticles intact. Second, the resonant interband transitions between the heavy and light parts of the hybridized conduction band that break the Kondo singlet. We find that the Kondo-singlet-breaking interband transitions do not create a Drude peak, while the Kondo-retaining intraband excitations yield the expected Drude response. This makes it possible to separate these two fundamentally different correlated contributions to the optical conductivity.

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Section: Resultssupporting

confidence: 64%

Terahertz conductivity of heavy-fermion systems from time-resolved spectroscopy

Yang

Pal

Zamani³

et al. 2020

Phys. Rev. Research

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“…Because the magnetic quantum phase transition is accompanied by the transition from a phase with asymptotically decoupled local-moment and conductionelectron degrees of freedom to one in which the entangling of the two turns the 4f local moments into composite quasiparticles, it is natural that both the single-particle and charge dynamics are critical. Indeed, calculations at the Kondo-destruction QCP in various large-N limits (Cai et al, 2020;Kirchner et al, 2005;Komijani and Coleman, 2019;Zhu et al, 2004) and, more recently, in the physical N = 2 case (Cai et al, 2020) have shown such a singular charge dynamics. Intriguingly, this type of charge dynamical scaling in models of the Kondo limit smoothly connects to the ω/T -scaling for the charge dynamics in the beyond-Landau-type quantum criticality in the mixed-valence regime (Pixley et al, 2012).…”

Section: Discussionmentioning

confidence: 97%

Colloquium : Heavy-electron quantum criticality and single-particle spectroscopy

et al. 2020

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Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) have become indispensable tools in the study of correlated quantum materials. Both probe complementary aspects of the single-particle excitation spectrum. Taken together, ARPES and STM have the potential to explore properties of the electronic Green function, a central object of many-body theory. In this article, we explicate this potential with a focus on heavy-electron quantum criticality, especially the role of Kondo destruction. We discuss how to probe the Kondo destruction effect across the quantum critical point using ARPES and STM measurements. We place particular emphasis on the question of how to distinguish between the signatures of the initial onset of hybridization-gap formation, which is the "high-energy" physics to be expected in all heavy-electron systems, and those of Kondo destruction, which characterizes the low-energy physics and, hence, the nature of quantum criticality. We survey recent progress and possible challenges in the experimental investigations, compare the STM and ARPES spectra for several quantum critical heavy-electron compounds, and outline the prospects for further advances. CONTENTS I. Introduction 2 II. Quantum criticality 3 A. High-energy excitations, temperature evolution and mass enhancement 5 B. Isothermal evolution at low temperatures 6 C. Further considerations 6 D. Summary of Section II 6 III. ARPES, STM, and the single-particle Green function 6 A. The one-particle Green function 7 B. ARPES and STM 7 C. Probing quantum criticality in the Kondo lattice 8 D. Summary of Section III 9 IV. Quantum criticality in YbRh 2 Si 2 9 Summary of Section IV 11 V. The Cerium-based 115 family: photoemission vs. tunneling spectroscopy 11 A. CeIrIn 5 11 B. CeCoIn 5 12 C. CeRhIn 5 14 D. Further considerations 15 E. Summary of Section V 16 VI. Progress, challenges and prospects 16 A. High energy Kondo features 16 B. Isothermal evolution at low temperatures 17 C. Outlook 17 VII. Conclusion 19 Acknowledgements 19 References 20

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“…8. Associated with the Kondo breakdown and development of a large Fermi surface, soft charge fluctuations can emerge without a change in formal valence of Ce ions 52 . Within experimental uncertainty of ±1.5%, there is no detectable difference between CeRhIn 5 and CeIrIn 5 at 10 K in their spectroscopically determined Ce valence 53 , even though their Fermi volumes differ-a result that, together with the phase diagram of Fig.…”

Section: Discussionmentioning

confidence: 99%

Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5

Kawasaki

Sorime

et al. 2020

Commun Phys

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A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure (P)-dependent 115 In nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh 0.5 Ir 0.5 In 5. These experiments reveal an antiferromagnetic (AF) QCP at P AF c ¼ 1:2 GPa where a dome of superconductivity reaches a maximum transition temperature T c. Preceding P AF c , however, the NQR frequency ν Q undergoes an abrupt increase at P Ã c = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium's f-electron and associated small-to-large change in the Fermi surface. At P AF c where T c is optimized, there is an unusually large fraction of gapless excitations well below T c that implicates spin-singlet, odd-frequency pairing symmetry.

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Emergent Critical Charge Fluctuations at the Kondo Breakdown of Heavy Fermions

Cited by 49 publications

References 53 publications

Terahertz conductivity of heavy-fermion systems from time-resolved spectroscopy

Terahertz conductivity of heavy-fermion systems from time-resolved spectroscopy

Colloquium : Heavy-electron quantum criticality and single-particle spectroscopy

Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5

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