Order on Command

Abstract

We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr 2 VO 3 FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C 4 (2 × 2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C 4 (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 C 4 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. DOI: 10.1103/PhysRevLett.119.227001 Iron-based superconductors (FeSCs) have shown intriguing phenomena related to the coexistence of magnetism and superconductivity below the superconducting transition temperature (T c ) [1][2][3]. Although an understanding of their detailed interplay is still under debate, certain magnetic orders seem to be very crucial in realizing coexistent superconductivity [3][4][5][6][7][8][9][10][11][12][13][14][15]. Recent studies have shown new reentrant C 4 symmetric antiferromagnetic phases (C 4 magnetism from now on) coexisting with superconductivity and have reported that the superconducting T c is suppressed by C 4 magnetic order [16][17][18][19]. Direct atomic-scale control of the Fe layer's magnetic symmetry and the determination of its correlation with superconductivity may be useful for an in-depth understanding of the interplay between superconductivity and magnetism. To our knowledge, there has been no report of a direct realspace observation of such a control by local probes and atomic-scale demonstration of the correlation of magnetism and superconductivity.In this regard, the parent compound tetragonal ironbased superconductor Sr 2 VO 3 FeAs with T c ≈ 33 K [20] is an ideal candidate where the interplay between magnetism and superconductivity can be directly demonstrated due to its nearly degenerate magnetic ground states. Sr 2 VO 3 FeAs has two types of square magnetic ion lattices: a square Fe lattice in the FeAs layer and a square V lattice in the two neighboring VO 2 layers. At optimal doping, the FeAs layer usually prefers C 2 magnetism harboring superconductivity, while the VO 2 layer prefers C 4 magnetism [1][2][3]21]. Previous experimental studies of Sr 2 VO 3 FeAs [22][23][24][25][26][27][28], however, have reported inconsistent results about magnetic order; recent nuclear magnetic resonance (NMR) measurements on single crystals [29] and neutron diffraction [30] experiments show that there is no long-range magnetic order in the V lattice at any temperature, while in the Fe lattice a magnetic order with a small moment of ∼0.05μ B , possibly due to frustration, i...

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