Optical observation of non-Fermi-liquid behavior in the heavy fermion state of $\mathrm{Yb}{\mathrm{Rh}}_2{\mathrm{Si}}_2$

We report far-infrared optical properties of $\mathrm{Yb}{\mathrm{Rh}}_2{\mathrm{Si}}_2$ for photon energies down to $2\mathrm{meV}$ and temperatures $0.4–300\mathrm{K}$. In the coherent heavy quasiparticle state, a linear dependence of the low-energy scattering rate on both temperature and photon energy was found. We relate this distinct dynamical behavior different from that of Fermi-liquid materials to the non-Fermi-liquid nature of $\mathrm{Yb}{\mathrm{Rh}}_2{\mathrm{Si}}_2$ which is due to its close vicinity to an antiferromagnetic quantum critical point.

Figure 1

(Color online) Temperature dependence of the reflectivity spectrum $R\left(\omega \right)$ in the photon energy range of $2–500\mathrm{meV}$. Inset: $R\left(\omega \right)$ at 5.5 and $300\mathrm{K}$ in the complete accessible range of photon energies up to $30\mathrm{eV}$.

Figure 2

(Color online) Temperature dependence of the optical conductivity $\sigma \left(\omega \right)$ (solid lines) with corresponding direct current conductivity (${\sigma }_{\mathit{DC}}$, symbols). Dashed lines: Classical Drude model with implicit Drude masses $m^{*}$ as indicated. Corresponding ${\sigma }_{\mathit{DC}}$ and carrier densities (derived from the Hall coefficient) were used.

Figure 3

(Color online) Temperature dependence of (a) the effective mass relative to the free-electron mass, $m^{*}\left(\omega \right)∕m_0$, and (b) the scattering rate $1∕\tau \left(\omega \right)$ as a function of photon energy $\hslash \omega$. The inset of (b) is the low-energy part of $1∕\tau \left(\omega \right)$. The dashed line emphasizes a $1∕\tau \propto \hslash \omega$ behavior.

Figure 4

(Color online) Temperature dependence of (a) the dynamical mass $m^{*}\left(T\right)∕m_0$ and (b) the scattering rate $1∕\tau (\omega ,T)$ at specific photon energies as indicated. The dashed line in (b) shows a non-Fermi-liquid $1∕\tau \propto T$ behavior.