X-ray diffuse scattering study of local distortions in Fe${}_{1+x}$Te induced by excess Fe

We report x-ray diffuse scattering studies of the iron chalcogenide Fe${}_{1+x}$Te as a function of doping and temperature for $x=0.03$, 0.08, and 0.12. In all cases, remarkably strong, characteristic diffuse scattering is observed. This scattering extends throughout the Brillouin zone and exhibits a nonmonotonic decay away from the fundamental Bragg peaks, with a peaklike structure at a reduced $q\approx (0.3,0,0.6)$. We interpret this scattering as Huang diffuse scattering resulting from distortions induced by the interaction between the excess Fe and the FeTe layers. The form of the scattering indicates that this interaction is strong and extends a number of unit cells away from the interstitial Fe site. Further, the diffuse scattering shows a sudden decrease on cooling through the structural and magnetic phase transition, reflecting the first-order change of the electronic structure of FeTe.

Figure 1

X-ray diffuse scattering pattern measured in the ($H$ 0 $L$) plane from (Top panel) Fe${}_{1.03}$Te and (Bottom panel) Fe${}_{1.12}$Te at $T=20$ K.

Figure 2

Simulation of Huang diffuse scattering intensity. (a), (b) Top and side views, respectively, for the force pattern used in the simulation. The direction and the length of the arrows indicate the direction and amplitude of the forces. The lengths of the down-pointing arrows (red) in (a) are amplified by a factor of 5 to be visible. Dashed lines indicate the coordination shells with respect to the excess Fe in the Fe2 site. (c) The calculated intensity in the ($H$0$L$) plane resulting from this force pattern.

Figure 3

(a), (c) $H$ scans as a function of temperature near $T_N$ for Fe${}_{1.03}$Te (taken at $L=6.7$) and Fe${}_{1.08}$Te (taken at $L=6.6$). (b), (d) Difference curves for the scattered intensity with respect to the lowest temperature shown in each case, for temperatures just below (red curves with open circles) and just above (blue curves with solid squares) $T_N$ for each sample.

Figure 4

Temperature dependence of the HDS intensities from Fe${}_{1.03}$Te (red curves with open circles and solid squares) and Fe${}_{1.08}$Te (blue curve with open diamonds) as measured at different $Q$ points. The dashed lines indicate $T_N$ for the two samples.