Unified trend of superconducting transition temperature versus Hall coefficient for ultrathin FeSe films prepared on different oxide substrates

Abstract

High transition temperature (${T}_{\mathrm{c}}$) superconductivity in FeSe/$\mathrm{SrTi}{\mathrm{O}}_{3}$ has been widely discussed on the possible mechanisms in conjunction with the various effects of interface between FeSe and $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate. By employing an electric-double-layer transistor configuration, which enables both the electrostatic carrier doping and electrochemical thickness tuning, we investigated the interfacial effect on the high-${T}_{\mathrm{c}}$ phase at around 40 K in FeSe films deposited on $\mathrm{SrTi}{\mathrm{O}}_{3}$, MgO, and $\mathrm{KTa}{\mathrm{O}}_{3}$ substrates. The systematic study on thickness dependence of transport properties under a certain gate voltage reveals the universal trend of the onset ${T}_{\mathrm{c}}$ against the Hall coefficient in all the FeSe films, irrespective of the substrate materials in which the different contribution of interfacial effect is expected. The independence of the highest ${T}_{\mathrm{c}}$ on substrate materials evidences that the high-${T}_{\mathrm{c}}$ superconductivity at around 40 K does not primarily originate from a specific interface combination but from a charge carrier filling at specific electronic band structure.