Positive and negative chemical pressure effects investigated in electron-doped FeSe films with an electric-double-layer structure

Abstract

We investigated chemical pressure effects in electron-doped (e-doped) FeSe by fabricating an electric-double-layer structure with single crystalline FeSe films on LaAlO3 with Se substituted by isovalent Te and S. Our method enables transport measurements of e-doped FeSe. Electron doping by applying gate voltage of 5 V increases Tc of the FeSe1−xTex and FeSe1−ySy films with 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.25, while the e-doped x = 0.5 film showed lower Tc than that of the undoped one. Both positive and chemical pressure suppress Tc of the e-doped FeSe. The obtained superconducting phase diagram in the e-doped samples is rather different from that in undoped samples. This might suggest that the superconductivity mechanism is different between undoped and e-doped systems. Alternatively, this is possibly explained by the absence of the nematic order in e-doped samples. ∗ [email protected]