專題演講

2018/11/06(Tue)     10:30 -12:00    5th Floor(1st meeting room)

Title

Discovery of Superconductivity Controlled by Spin Current

Speaker

Prof. Jhinhwan Lee

Department of Physics, Korea Advanced Institute of Science and Technology

Abstract

We have explored a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SP-STM) [1,2]. Our SPSTM study on single crystal Sr2VO3FeAs made of alternating self-assembled FeAs monolayer and Sr2VO3 bilayers shows that a spin-polarized tunneling current can switch the FeAs-layer magnetism into a non-trivial C4 (2×2) order, which cannot be achieved by thermal excitation with unpolarized current. Our tunneling spectroscopy study shows that the induced C4 (2×2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C4 state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors [3,4]. To seek enhancement of the operating temperature of the possible device controlling superconductivity, we provide high-resolution quasiparticle interference (QPI) measurements correlated with the gap map and the charged atomic defects whose analysis shows an atomic-scale proof of enhancement of superconductivity due to the forward-scattering interfacial phonons natively existing in many heterostructures [5]. I will also briefly present our SP-STM and spin-polarized QPI study on the itinerant spin transport channels confined to the potential walls of the atomic vacancy network on the triangular-lattice Pd monolayer on cleaved delafossite PdCrO2 single crystal [6].

[1] Jin-Oh Jung et al., Rev. Sci. Instrum. 88, 103702 (2017)
[2] Jhinhwan Lee, Rev. Sci. Instrum. 88, 085104 (2017)
[3] Seokhwan Choi et al., Phys. Rev. Lett. 119, 227001 (2017)
[4] Dirk van der Marel, Physics 10, 127 (2017)
[5] Seokhwan Choi et al., Phys. Rev. Lett. 119, 107003 (2017)
[6] Jin-Oh Jung et al., in preparation.