Collapse of the $G{d}^{3+}$ ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor $CeF{e}_4{P}_{12}$

Abstract

Experiments on the $G{d}^{3+}$ Electron Spin Resonance (ESR) in the filled skutterudite $C{e}_{1-x}G{d}_{x}F{e}_4{P}_{12}$ ($x\approx 0.001$), at temperatures where the host resistivity manifests a smooth insulator-metal crossover, provides evidence of the underlying Kondo physics associated with this system. At low temperatures (below $T\approx K$), $C{e}_{1-x}G{d}_{x}F{e}_4{P}_{12}$ behaves as a Kondo-insulator with a relatively large hybridization gap, and the $G{d}^{3+}$ ESR spectra displays a fine structure with lorentzian line shape, typical of insulating media. The electronic gap is attributed to the large hybridization present in the coherent regime of a Kondo lattice, when Ce 4f-electrons cooperate with band properties at half-filling. Mean-field calculations suggest that the electron-phonon interaction is fundamental at explaining the strong 4f-electron hybridization in this filled skutterudite. The resulting electronic structure is strongly temperature dependent, and at about $T^{\ast }\approx 160K$ the system undergoes an insulator-to-metal transition induced by the withdrawal of 4f-electrons from the Fermi volume, the system becoming metallic and non-magnetic. The $G{d}^{3+}$ ESR fine structure coalesces into a single dysonian resonance, as in metals. Still, our simulations suggest that exchange-narrowing via the usual Korringa mechanism, alone, is not capable of describing the thermal behavior of the ESR spectra in the entire temperature region ($4.2$ - $300$ K). We propose that temperature activated fluctuating-valence of the Ce ions is the missing ingredient that, added to the usual exchange-narrowing mechanism, fully describes this unique temperature dependence of the $G{d}^{3+}$ ESR fine structure observed in $C{e}_{1-x}G{d}_{x}F{e}_4{P}_{12}$.

19 pages, 6 figures

References in corpus (3)

• Transport properties in CeOs${}_4$Sb${}_{12}$: Possibility of the ground state being semiconducting
• Anisotropic spin-dynamics in the Kondo semiconductor CeRu2Al10
• Contrasting electron and hole doping effects on the spin gap of the caged type Kondo semimetal CeOs${}_2$Al${}_{10}$: A muon spin relaxation and inelastic neutron scattering investigation

Cited by in corpus (3)

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