In-plane Resistivity Anisotropy in Mechanically De- twinned Single Crystals FeSe

The in-plane resistivity anisotropy was studied in stress-detwinned vapor transport grown single crystals of FeSe, which exhibit the tetragonal-orthorhombic structural transition temperature at $T_s \sim $ 90 K in unstrained samples, but no long-range magnetic order. Direct transport and elastoresistivity measurements show a significant in-plane resistivity anisotropy above $T_s$ induced by a very moderate mechanical stress. This anisotropy peaks slightly below $T_s$ and decreases to nearly zero on cooling to base temperature, while the degree of orthorhombic distortion grows monotonically before saturating at low temperatures. We explain the non-monotonic temperature dependence of the resistivity anisotropy as a result of the inelastic scattering of electrons by anisotropic spin fluctuations. Experimental work was supported by the U.S. DOE/OS/MSED and was performed at the Ames Laboratory, Iowa State University under contract DE-AC02-07CH11358. M.S. acknowledges the support from the Humboldt Foundation. R.M.F. is supported by the U.S. DOE, Office of Science, Basic Energy Sciences, under Award No. DE-SC0012336.