We have investigated correlation between structural and electronic anisotropies in a parent compound of Fe-chalcogenide superconductor ${\mathrm{Fe}}_{1+\delta }\mathrm{Te}$ with $\delta =0.09$ by means of synchrotron x-ray diffraction and in situ in-plane resistivity anisotropy measurements with uniaxial stress applied along a tetragonal $a$ axis. This system is known to exhibit a tetragonal-to-monoclinic structural transition at $T_{\mathrm{S}}\sim 60$ K. We have confirmed that the in-plane resistivity anisotropy in the low-temperature monoclinic phase is attributed to the asymmetry in volume fractions of the monoclinic domains, as was suggested in a previous study [Jiang et al., Phys. Rev. B 88 115130 (2013)]. On the other hand, we found another in-plane resistivity anisotropy above $T_{\mathrm{S}}$. The present x-ray diffraction and resistivity anisotropy measurements have revealed that this anisotropy is not due to an onset of the low-temperature monoclinic phase but to the lattice softening enhanced toward $T_{\mathrm{S}}$. As one of the possibilities, we suggest that the orbital fluctuation contributes to the lattice softening and the resistivity anisotropy above $T_{\mathrm{S}}$.

• Received 2 February 2015
• Revised 5 May 2015

DOI:https://doi.org/10.1103/PhysRevB.91.205125