Intersite Coupling Effects in a Kondo Lattice

The La dilution of the Kondo lattice ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$ is studied. The scaling laws found for the magnetic susceptibility and the specific heat reveal two well-separated energy scales, corresponding to the single-impurity Kondo temperature $T_K$ and an intersite spin-liquid temperature $T^{*}$. The Ce-dilute alloy has the expected Fermi liquid ground state, while the specific heat and resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which scales with $T^{*}$. These observations indicate that the screening of the magnetic moments in the lattice involves antiferromagnetic intersite correlations with a larger energy scale in comparison with the Kondo impurity case.

Figure 1

Magnetic in-plane resistivity ${\rho }_m$ for various $x$ of ${\mathrm{C}\mathrm{e}}_{1-x}{\mathrm{L}\mathrm{a}}_x{\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$. Right inset: The log-log plot for the inelastic part of ${\rho }_m$ vs $T/T_{\mathrm{c}\mathrm{o}\mathrm{h}}$; the solid line is the $T$ linear fit and the vertical lines mark the onset of superconductivity. Left inset: ${\rho }_m$ vs $T^2$ for the incoherent regime.

Figure 2

Excess susceptibility $\Delta \chi (T)\equiv \chi (T)-{\chi }_0(T)$ (${\chi }_0(T)$ refers to the single-impurity limit at $x=0.955$), scaled with $T/T^{*}$. The solid line corresponds to an activation type fit. Inset: the $c$-axis component of $M/H$ vs $\log T$.

Figure 3

$C_m/T$ times $T^{*s}$ vs $T/T^{*s}$. The solid line represents the $-\ln T$ fit. Left inset: $T$ dependence of $C_m$ for $x=0.98$ and 0.99. The solid curve is the fit to the $S=1/2$ Kondo impurity limit with $T_K=1.7\mathrm{K}$. Right inset: $T$ dependence of $C_m$. The solid curve is the fit based on our CEF scheme.

Figure 4

Energy scale diagram of ${\mathrm{C}\mathrm{e}}_{1-x}{\mathrm{L}\mathrm{a}}_x{\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$. $T_{\mathrm{s}\mathrm{c}}$ is the superconducting transition temperature determined by the onset of the jump observed in $C_P(T)$. $T_{\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}}$ and $T_{\mathrm{F}\mathrm{L}}$ are the temperatures below which the resistivity starts to show $T$ linear and $T^2$ dependence. $T^{*ab}$, $T^{*c}$, and $T^{*s}$ are the characteristic temperatures of the $ab$-plane and $c$-axis susceptibilities, and the specific heat, respectively.