Biaxial strain is one of the effective parameters to control physical properties of materials. The band structure of iron-based superconductors is sensitive to the local crystal structure, and hence it is expected that application of biaxial strain gives rise to a significant change in physical properties. Indeed, angle-resolved photoemission spectroscopy measurements revealed a systematic change of the band structure in thin films of FeSe with various degrees of in-plane biaxial strain [1]. Reflecting the band structure, superconducting transition temperature T_c also shows a systematic change with strain [2]. Although a study using thin films turned out to be effective, the quality of the film varies depending on substrate materials, and compounds to which such an approach is applicable would be limited. Here we report the electronic transport properties for FeSe single crystals with applying biaxial strain ε ranging from -0.9% to 0.2%. FeSe single crystals were firmly glued on various substrate materials with different thermal expansion. T_c monotonically decreased with increasing ε, consistent with the study on the thin films [2]. We analyzed magneto-transport data using a compensated three-carrier model, in which one hole and two electron carriers are considered. The result for the strain-free sample is in agreement with the previous study [3]. The evaluated densities of hole and electron carriers systematically decreased with increasing ε. This indicates that we definitely succeeded in controlling the band structure of single-crystalline FeSe via biaxial strain.

[1] G. N. Phan et al., Phys. Rev. B 95, 224507 (2017).
[2] F. Nabeshima et al., Jpn. J. Appl. Phys. 57, 120314 (2018).
[3] M. D. Watson et al., Phys. Rev. Lett. 115, 027006 (2015).

Keywords: iron-based superconductors, FeSe, biaxial strain, transport properties