Thin-film Superconductor FeSe : Scanning Tunneling Microscopy Study

Abstract

Since the discovery of superconducting phenomena by H. K. Onnes in 1911[1], superconductors have become a major research field in the solid states physics. Numerous physicists have discovered new superconductors and are working to physically explain superconductivity phenomena. In surface science, superconductors are also an interesting research topic. It mainly studies how low-dimensional physical phenomena appear in superconductors and how superconductivity itself changes at low dimension. I have studied superconductivity phenomenon in low dimension, especially two dimension, using scanning tunneling microscope (STM). The superconducting samples used in the study are tetragonal FeSe on SrTiO3(100) and hexagonal FeSe on SrTiO3(100). Tetragonal FeSe has the simplest structure among the iron chalcogenide superconductor. In 2012, the Xues group in China found that when 1 ML FeSe was grown on SrTiO3(100), the critical temperature rose to over 60 K [2], many physicists have gone into this study and tried to figure out why the critical temperature has improved . This study was initiated to clarify the pairing mechanism of tetragonal FeSe on SrTiO3(100). I analyzed the spectroscopy of STM and found the frequency of the bosonic mode that is involved in the Cooper pairing using the Eliashberg model. And I tried to find out what the expected bosonic mode is. Next, hexagonal FeSe, which is a new phase of FeSe, was grown on SrTiO3(100) and its physical properties were measured using STM. The newly discovered hexagonal phase FeSe shows many experimental results consistent with the superconducting phenomenon, but further studies are needed to confirm it as a new superconductor.