| Summary: | 碩士 === 國立臺灣大學 === 應用物理研究所 === 107 === Superconductivity of the monolayer Iron Selenide (FeSe) on Strontium titanate (SrTiO3, STO) substrate has drawn a great deal of interest due to the unusual superconducting phenomena. Recent studies speculated that the critical temperature (Tc) is dependent of the substrate-surface reconstruction. Different substrate-induced reconstruction resulted in the variation of the electron accumulation in the FeSe monolayer. However, the argument was only supported by the measurements detecting on the top surface of the FeSe monolayer. Direct evidence of the evolution of the electronic structure across the FeSe/STO interface with atomic-resolution is still lacking.
In this work, we utilize cross-sectional scanning tunneling microscopy and spectroscopy to study the electronic structure directly at the interface between FeSe and STO. Two substrate-induced reconstructions are investigated: one is the √13 × √13 reconstruction terminated on the STO surface, and the other one is the √20 × √20 reconstruction terminated on the STO surface. Our experimental results clearly demonstrate the amount of surface carriers on the STO surface’s √13 × √13 reconstruction is 1.2 times to that on the √20 × √20 reconstruction, and the increased carrier density from different reconstruction enhances the critical temperature of the FeSe monolayer by 3K.
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