Multiple energy gap features of superconducting FeSe investigated by tunneling spectroscopy

摘要

Planar tunneling junctions of the presumably unconventional superconductorFeSe were prepared and investigated. The junctions consisted of FeSe/AlOx/Agmultilayers patterned lithographically into mesa structures. Bias voltagedependent differential conductivities dI/dV(V) of junctions in the tunneling,intermediate barrier strength, and metallic regimes were investigated.Depending on the barrier type between two and four features of the conductivitywere obtained, which are discussed in the framework of multiple superconductingenergy gaps. Specifically we reproduced with all barrier types an establishedenergy gap and discovered an additional large gap structure. From two furtherconductivity features presumable one originates from another superconductinggap and the other from resonant states.