Optical observation of non-fermi-liquid behavior in the heavy fermion state of YbRh2Si2

We report far-infrared optical properties of $\mathrm{Yb}{\mathrm{Rh}}_{2}{\mathrm{Si}}_{2}$ for photon energies down to $2\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ and temperatures $0.4\char21{}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. 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.