Spectral weight transfer in strongly correlated ${\mathrm{Fe}}_{1.03}\mathrm{Te}$

The temperature dependence of the in-plane optical conductivity has been determined for ${\mathrm{Fe}}_{1.03}\mathrm{Te}$ above and below the magnetic and structural transition at $T_N\simeq 68$ K. The electron and hole pockets are treated as two separate electronic subsystems: a strong, broad Drude response that is largely temperature independent, and a much weaker, narrow Drude response with a strong temperature dependence. Spectral weight is transferred from high to low frequency below $T_N$, resulting in the dramatic increase of both the low-frequency conductivity and the related plasma frequency. The change in the plasma frequency is due to an increase in the carrier concentration resulting from the closing of the pseudogap on the electron pocket, as well as the likely decrease of the effective mass in the antiferromagnetic state.

Figure 1

(a) The reflectance of ${\mathrm{Fe}}_{1.03}\mathrm{Te}$ in the far-infrared region for light polarized in the Fe-Te planes at several temperatures above and below $T_N$. Inset: The temperature dependence of the in-plane resistivity. (b) The high-frequency reflectance at 295 and 5 K.

Figure 2

The temperature dependence of the real part of the optical conductivity of ${\mathrm{Fe}}_{1.03}\mathrm{Te}$ for light polarized in the a-b planes above and below $T_N$ (the origin for the $y$ axis is offset). The symbols denote the values for the dc conductivity obtained from transport measurements. Inset: the temperature dependence of the optical conductivity shown over a larger energy scale showing the transfer of spectral weight from high to low energy below $T_N$. The arrow indicates the energy scale in the optical conductivity for the pseudogap on the electron pocket in the PM state.

Figure 3

The temperature dependence of the normalized spectral weight as a function of cut-off frequency, ${\omega }_c$. For values of ${\omega }_c\gtrsim 4000{\mathrm{cm}}^{-1}$ the spectral weight is completely captured and no temperature dependence is observed.

Figure 4

The low-frequency in-plane optical conductivity of ${\mathrm{Fe}}_{1.03}\mathrm{Te}$ with the broad Drude contribution and the Lorentz oscillators removed. The symbols at the origin denote ${\sigma }_{dc}-{\sigma }_{D2}$ (see text). The dotted line denotes $1/{\tau }_{D,1}=6$ meV, while the dashed lines are Drude fits at 75 and 10 K using the values from Table 1. Inset: the square of the normalized plasma frequency for the narrow Drude component versus the reduced temperature; the dotted line denotes mean-field behavior.