Magneto-optical behavior of ${\mathrm{EuIn}}_2{\mathrm{P}}_2$

We report results of a magneto-optical investigation of the Zintl-phase compound ${\mathrm{EuIn}}_2{\mathrm{P}}_2$. The compound orders magnetically at $T_C=24\mathrm{K}$ and exhibits concomitant large magnetoresistance effects. For $T\le 50\mathrm{K}$ and increasing magnetic fields we observe a transfer of spectral weight in ${\sigma }_1\left(\omega \right)$ from energies above $1\mathrm{eV}$ into the low-energy metallic component as well as into a midinfrared signal centered at about $600{\mathrm{cm}}^{-1}$. This latter absorption is reminiscent to what has been seen in a large variety of so-called Kondo materials and ascribed to excitations across the hybridization gap. The observed gain of Drude weight upon increasing magnetic field suggests an enhancement of the itinerant charge-carrier concentration due to the increasing magnetization, a phenomenon that was previously observed in other compounds that exhibit colossal magnetoresistive effects.

Figure 1

(Color online) Reflectivity spectra $R\left(\omega \right)$ of ${\mathrm{EuIn}}_2{\mathrm{P}}_2$ in the infrared spectral range as a function of temperature at $B=0\mathrm{T}$ (a). Panels (b) and (c) show $R\left(\omega \right)$ at 10 and $30\mathrm{K}$, and in magnetic fields between 0 and $7\mathrm{T}$, respectively. The inset in panel (a) displays $R\left(\omega \right)$ at $300\mathrm{K}$ in the whole measured spectral range (logarithmic energy scale). The inset in panel (c) shows the comparison between the ${\sigma }_{dc}$ values inserted in the HR extrapolation and the dc data[4] at $30\mathrm{K}$ and as a function of magnetic field.

Figure 2

(Color online) Real part ${\sigma }_1\left(\omega \right)$ of the low-frequency optical conductivity of ${\mathrm{EuIn}}_2{\mathrm{P}}_2$ at $30\mathrm{K}$ and as a function of magnetic field on a logarithmic energy scale. The Lorentz-Drude fit components (broken and dotted lines) are displayed for the $0\mathrm{T}$ spectra. The inset emphasizes ${\sigma }_1\left(\omega \right)$ and its Lorentz components in the high-frequency spectral range (linear energy scale).

Figure 3

(Color online) (a) Plasma frequency ${\omega }_p$ and (b) Drude scattering rate $\Gamma$, as a function of magnetic field at 10, 30, and $50\mathrm{K}$.

Figure 4

(Color online) Magnetic field dependence of the spectral weight distribution at (a) 10, (b) 30, and (c) $50\mathrm{K}$ in the effective metallic component $[S_{\mathrm{metallic}}={\omega }_p^2(\mathrm{Drude})+{\omega }_p^2(150{\mathrm{cm}}^{-1}\left)\right]$, the lattice phonon mode $[S_{\mathrm{phonon}}={\omega }_p^2(270{\mathrm{cm}}^{-1})+{\omega }_p^2(310{\mathrm{cm}}^{-1}\left)\right]$ and the hybridization gap feature $[S_{\mathrm{hybr}}={\omega }_p^2(600{\mathrm{cm}}^{-1})+{\omega }_p^2(590{\mathrm{cm}}^{-1}\left)\right]$. ${\omega }_p^2$ is the squared plasma frequency and mode strength for the Drude term and HO at the resonance frequency given in parentheses, respectively.