arXiv 1607.046202016-07-15cond-mat.str-el

掺Gd近藤半导体$CeFe_{4}P_{12}$在整个相干温度下$Gd^{3+}$ ESR精细结构的崩塌

Collapse of the $Gd^{3+}$ ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor $CeFe_{4}P_{12}$

P. A. Venegas, F. A. Garcia, D. J. Garcia, G. Cabrera, M. A. Avila, C. Rettori

备注：: 19 pages, 6 figures
发表信息：: Phys. Rev. B 94, 235143 (2016)
DOI：: 10.1103/PhysRevB.94.235143

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摘要：

在填充方钴矿$Ce_{1-x}Gd_{x}Fe_{4}P_{12}$（$x \approx 0.001$）中的$Gd^{3+}$电子自旋共振（ESR）实验，在宿主电阻率表现出平滑的绝缘体-金属交叉的温度下，提供了与该系统相关的基本近藤物理学的证据。在低温下（低于$T \approx K$），$Ce_{1-x}Gd_{x}Fe_{4}P_{12}$表现为具有相对大的杂化间隙的Kondo绝缘体，并且$Gd^{3+}$ ESR谱显示具有洛伦兹线形状的精细结构，这是绝缘介质的典型。的电子间隙是由于大的杂化存在于相干制度的近藤晶格，当Ce 4f-电子配合在半填充的能带特性。平均场计算表明，电子-声子相互作用是解释强4f-电子杂化在这个填充方钴矿的基本。所得到的电子结构是强烈的温度依赖性，并在约$T^{*} \approx 160 K$的系统经历绝缘体到金属的转变所引起的4f-电子从费米体积，该系统成为金属和非磁性的撤回。$Gd^{3+}$ ESR精细结构合并为单个戴森共振，就像金属中一样。尽管如此，我们的模拟表明，通过通常的Korringa机制，单独的交换窄化，是不能描述的ESR谱在整个温度范围内（$4.2$ - $300$ K）的热行为。我们建议，温度激活波动价的Ce离子是缺少的成分，添加到通常的交换窄化机制，充分描述了这种独特的温度依赖性的$Gd^{3+}$ ESR精细结构中观察到的$Ce_{1-x}Gd_{x}Fe_{4}P_{12}$。

英文摘要：

Experiments on the $Gd^{3+}$ Electron Spin Resonance (ESR) in the filled skutterudite $Ce_{1-x}Gd_{x}Fe_{4}P_{12}$ ($x \approx 0.001$), 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 $T \approx K$), $Ce_{1-x}Gd_{x}Fe_{4}P_{12}$ behaves as a Kondo-insulator with a relatively large hybridization gap, and the $Gd^{3+}$ 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 $T^{*} \approx 160 K$ 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 $Gd^{3+}$ 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 $Gd^{3+}$ ESR fine structure observed in $Ce_{1-x}Gd_{x}Fe_{4}P_{12}$.

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