Chemical pressure effect of the electron-doped FeSe films with an electric double-layer-transistor structure

Abstract

We investigated chemical pressure effect of the electron-doped FeSe1−x S x and FeSe1−y Te y on LaAlO3 (x ≤ 0.25, y ≤ 0.5) with the electric double layer transistor structure. T c of all the FeSe1−x S x and FeSe1−y Te y films except y = 0.5 is increased by doping electron with gate voltage V G = +5 V. T c of the electron-doped FeSe1−x S x and FeSe1−y Te y is decreased monotonically by substituting Se for both S and Te. The behavior is similar to those of the intercalated FeSe1−x S x and FeSe1−y Te y and the electron-doped FeSe0.5Te0.5 with the solid-ion-conductor field-effect transistor structure, but quite different from that of the pristine FeSe1−x S x and FeSe1−y Te y . This difference is considered to originate from the difference of the Fermi surface topology, which suggests that the superconducting mechanism of the electron-doped FeSe is different from that of the pristine FeSe.