Controlling iron-basedsuperconductivity with spin currents
Department of Physics,Korea Advanced Institute of Science and Technology, Republic of Korea
We have explored a new mechanism for switchingmagnetism and superconductivity in a magnetically frustrated iron-basedsuperconductor using spin-polarized scanning tunneling microscopy (SPSTM) [1,2].Our SPSTM study on single crystal Sr2VO3FeAs made ofalternating self-assembled FeAs monolayer and Sr2VO3bilayers shows that a spin-polarized tunneling current can switch the FeAs-layermagnetism into a non-trivial C4 (2×2) order, which cannot beachieved by thermal excitation with unpolarized current. Our tunnelingspectroscopy study shows that the induced C4 (2×2) order hascharacteristics of plaquette antiferromagnetic order in the Fe layer andstrongly suppresses superconductivity. Also, thermal agitation beyond the bulkFe spin ordering temperature erases the C4 state. These resultssuggest a new possibility of switching local superconductivity by changing thesymmetry of magnetic order with spin-polarized and unpolarized tunnelingcurrents in iron-based superconductors [3,4]. We also performed high-resolutionquasiparticle interference (QPI) measurements, self-consistent BCS-theory-basedQPI simulations and a detailed e-ph coupling analysis to provide directatomic-scale proofs of enhancement of iron-based superconductivity due to theBCS mechanism based on forward-scattering interfacial phonons .
 Jin-Oh Jung et al., Rev. Sci. Instrum. 88,103702 (2017)
 Jhinhwan Lee, Rev. Sci. Instrum. 88, 085104 (2017)
 Seokhwan Choi et al., Phys. Rev. Lett. 119,227001 (2017)
 Dirk van der Marel, Physics 10, 127 (2017)
 Seokhwan Choi et al., Phys. Rev. Lett. 119,107003 (2017)
Fig. 1. (a)-(b) Atomic scale evidence of C4 antiferromagnetic order induced in FeAs layer of Sr2VO3FeAs by injection of spin-polarized tunneling current and (c)-(d) resultant local suppression of iron-based superconductivity . (e)-(f) Spectroscopic evidences of local enhancement of iron-based superconductivity due to oxygen vacancies in VO2 layer (rice-shaped C2 defects in (e)) which locally enhance coupling of FeAs electrons with the forward-scattering interfacial phonons .