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Controlling iron-based superconductivity with spin currents

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Date and time Mar 19, 2018
from 02:00 PM to 03:00 PM
Location 60 St. George Street, MP 606
Host Yong Baek Kim

Jhinhwan Lee

Department of Physics, Korea Advanced Institute of Science and Technology

We have explored a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM) [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]. We also performed high-resolution quasiparticle interference (QPI) measurements, self-consistent BCS-theory-based QPI simulations and a detailed e-ph coupling analysis to provide direct atomic-scale proofs of enhancement of iron-based superconductivity due to the BCS mechanism based on forward-scattering interfacial phonons [5].

[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)

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 [3]. (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 [5].Lee abstract

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