fitting analysis. Figure \[fig:ref\](b) shows the actual infrared and visible reflectivity data at 300K along with the output of the VDF fitting. In addition to reflectivity, the dc conductivity at each temperature as obtained from 4-probe resistivity measurements (see figure \[fig:ref\](c)) have also been used to constrain the VDF fitting subroutine. The real and imaginary parts of the complex conductivity thus obtained are shown in figure \[fig:sigma\](a) and \[fig:sigma\](b) respectively.

We model the low frequency response ($<$150 cm$^{-1}$) for all temperatures by a single Drude oscillator. Figure \[fig:ref\](c) shows the Drude scattering rate, $\Gamma_D$, as a function of temperature. Note that the temperature dependence of $\Gamma_D$ scales as resistivity within experimental error. At low temperatures, the resistivity of YbMnBi$_2$ has a strong temperature dependence showing the dominant role of inelastic scattering from either electron-electron or electron-phonon interactions. The similarity in temperature dependence of resistivity and $\Gamma_D$ thus points to the coherent nature of the quasiparticles within the Drude subsystem. The measured Drude plasma frequency at 5K is 1.74 eV.

The two most prominent features in the real part of the optical conductivity are the low energy peaks around 200 cm$^{-1}$ and 950 cm$^{-1}$. Such peaks in conductivity are ordinarily attributed 