Center for Artificial Low Dimensional Electronic Systems

Thin-film Superconductor FeSe : Scanning Tunneling Microscopy Study

Minjun Lee

January 22(Mon) - January 22(Mon), 2018

Thin-film Superconductor FeSe : Scanning Tunneling Microscopy Study

Minjun Lee

Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea

Since the discovery of superconducting phenomena by H. K. Onnes in 1911, 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 is the simplest superconductor of the iron chalcogenide superconductor. In 2012, the Xue’s group in China found that when 1 ML FeSe was grown on SrTiO₃(100), the critical temperature rose to over 60K, 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 in 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.

Keywords : superconductor, thin-film superconductor, iron selenide, scanning tunneling microscopy