Optical Study of Interactions in a $d$-Electron Kondo Lattice with Ferromagnetism

We report on a comprehensive optical, transport, and thermodynamic study of the Zintl compound ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$, demonstrating that it is the first ferromagnetic Kondo lattice compound in the underscreened limit. We propose a scenario whereby the combination of Kondo and Jahn-Teller effects provides a consistent explanation of both transport and optical data.

Figure 1

$R(\omega )$ of ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ at six temperatures. Inset: ${\omega }_p(T)$ [${\tilde{\omega }}_p(T)$] as described in the text.

Figure 2

${\sigma }_1(\omega )$ of ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ at all measured temperatures. The clear development of a low temperature coherent peak can be seen. Inset: (solid and dashed lines) $\frac{m^{*}(\omega )}{m_e}$ from the extended Drude analysis and the fit using Fermi’s golden rule and the density of states in Fig. 4b (blue circle) from the specific-heat analysis as described in the text.

Figure 3

(Black lines) $\frac{1}{\tau (\omega ,T)}$ data with an interpolated surface; see Eq. (2). (Gray line) the scattering rate from the dc resistivity $\rho (T)=\frac{1}{{\omega }_p^2(T)\tau (T)}$], and (light blue line) fit to $\frac{1}{\tau (\omega ,7\mathrm{K})}$.

Figure 4

(a) ${\sigma }_1(\omega ,7\mathrm{K})$ with a Drude and hybridization gap fit [3]. (b) $N(\omega {)}_{\uparrow ,\downarrow }$ that fits the measured $\frac{1}{\tau (\omega ,7\mathrm{K})}$, as described in the text. (c) Mean free path determined from dc resistivity $\rho (T)=\frac{3{\pi }^2\hslash }{e^2{k}_{\mathrm{F}}^2(T)l(T)}$. (d) Diagram of the temperature dependence of the electronic structure of ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ consistent with our measurements.