Chemical pressure effect of electron-doped FeSe films

The superconducting transition temperature (T_c) of FeSe increases from 9 K in bulk to 40-45 K with electron doping. To search for higher T_c, it is interesting to study the chemical pressure effect for the electron-doped FeSe. We fabricated the electric double layer transistor configuration of FeSe_1-xS_x and FeSe_1-yTe_y films for wide range of x and y, and measured transport properties under finite gate voltage.
Increasing S and Te content decreases T_c of electron-doped FeSe_1-xS_x and FeSe_1-yTe_y in a similar manner. This T_c behavior of electron-doped samples is very different from that of non-doped samples [1]. On the other hand, this behavior agrees well with that of the intercalated FeSe_1-xS_x and FeSe_1-yTe_y, whose T_c is also around 40 K. Our results suggest that the mechanism of superconductivity is different between 25 K class non-doped case and 40 K class doped case.

[1] F. Nabeshima et al., JPSJ 87, 073704 (2018).