Closing of the pseudogap in Fe$_{\mathbf{1.03}}$Te

The optical properties of strongly-correlated Fe$_{1.03}$Te have been measured over a wide frequency range for light polarized in the \emph{a-b} planes at temperatures above and below the structural and magnetic transition, $T_N\simeq 68$~K. For $T>T_N$, in the paramagnetic state, the resistivity is increasing with decreasing temperature, and the optical conductivity is flat over much of the infrared region, except for a weak Drude-like response at low frequency. Below $T_N$, in the antiferromagnetic state, there is dramatic increase in the low-frequency conductivity with a commensurate transfer of spectral weight (area under the conductivity curve) from high to low energy. The roughly constant value of the scattering rate indicates that it is the plasma frequency ($\omega_p$) that is increasing. This increase in $\omega_p^2\propto n/m^\ast$ is associated with the closing of the pseudogap on the electron pocket resulting in an increase in the number of carriers ($n$). In addition, below $T_N$ the effective mass ($m^\ast$) is also thought to decrease. Both effects lead to an increase in $\omega_p$ on the electron pocket.\footnote{Y. M. Dai {\em et al.}, Phys. Rev. B {\bf 90}, 121114(R) (2014).}