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Imaging the evolution of metallic states in a correlated iridate


The Ruddlesden–Popper series of iridates (Srn+1IrnO3n+1) have been the subject of much recent attention due to the anticipation of emergent phenomena arising from the cooperative action of spin–orbit-driven band splitting and Coulomb interactions1,2,3. However, an ongoing debate over the role of correlations in the formation of the charge gap and a lack of understanding of the effects of doping on the low-energy electronic structure have hindered experimental progress in realizing many of the predicted states4,5,6,7,8,9. Using scanning tunnelling spectroscopy we map out the spatially resolved density of states in Sr3Ir2O7 (Ir327). We show that its parent compound, argued to exist only as a weakly correlated band insulator, in fact possesses a substantial ~ 130 meV charge excitation gap driven by an interplay between structure, spin–orbit coupling and correlations. We find that single-atom defects are associated with a strong electronic inhomogeneity, creating an important distinction between the intrinsic and spatially averaged electronic structure. Combined with first-principles calculations, our measurements reveal how defects at specific atomic sites transfer spectral weight from higher energies to the gap energies, providing a possible route to obtaining metallic electronic states from the parent insulating states in the iridates.

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Figure 1: Topographic images of Sr3Ir2O7.
Figure 2: Tunnelling spectra across a chemical defect.
Figure 3: GGA+U band calculation along high-symmetry lines.
Figure 4: Visualization of the rotation angles of the underlying iridium oxide layer through crystal defects.
Figure 5: Spatial evolution of tunnelling spectra.

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  1. Kim, B. J. et al. Novel Jeff = 1/2 Mott state induced by relativistic spin–orbit coupling in Sr2IrO4 . Phys. Rev. Lett. 101, 076402–076405 (2008).

    Article  CAS  Google Scholar 

  2. Kim, B. J. et al. Phase-sensitive observation of a spin–orbital Mott state in Sr2IrO4 . Science 323, 1329–1332 (2009).

    Article  CAS  Google Scholar 

  3. Moon, S. J. et al. Dimensionality-controlled insulator-metal transition and correlated metallic state in 5d transition metal oxides Srn+1IrnO3n+1 (n = 1, 2, and ). Phys. Rev. Lett. 101, 226402–226405 (2008).

    Google Scholar 

  4. Jackeli, G. & Khaliullin, G. Mott insulators in the strong spin–orbit coupling limit: From Heisenberg to a quantum compass and Kitaev models. Phys. Rev. Lett. 102, 017205–017208 (2009).

    Article  CAS  Google Scholar 

  5. Shitade, A. et al. Quantum spin Hall effect in a transition metal oxide Na2IrO3 . Phys. Rev. Lett. 102, 256403–256406 (2009).

    Article  Google Scholar 

  6. Wan, X. et al. Topological semimetal and Fermi-arc surface states in the electronic structure of pyrochlore iridates. Phys. Rev. B 83, 205101–205109 (2011).

    Article  Google Scholar 

  7. Wang, F. & Senthil, T. Twisted Hubbard model for Sr2IrO4: Magnetism and possible high temperature superconductivity. Phys. Rev. Lett. 106, 136402–136405 (2011).

    Article  Google Scholar 

  8. Pesin, D. & Balents, L. Mott physics and band topology in materials with strong spin–orbit interaction. Nature Phys. 6, 376–381 (2010).

    Article  CAS  Google Scholar 

  9. Carter, J. M., Shankar, V. V. & Kee, H. Y. Theory of magnetic structure in layered iridates: Spin–orbit band or Mott insulators. Preprint at (2012).

  10. Kane, C. L. & Mele, E. J. Z2 topological order and the quantum spin Hall effect. Phys. Rev. Lett. 95, 146802–146805 (2005).

    Article  CAS  Google Scholar 

  11. Hasan, M. Z. & Kane, C. L. Topological insulators. Rev. Mod. Phys. 82, 3045–3067 (2010).

    Article  CAS  Google Scholar 

  12. Nagaosa, N. & Tokura, Y. Emergent electromagnetism in solids. Phys. Scr. T146, 014020–014035 (2012).

    Article  Google Scholar 

  13. Mühlbauer, S. et al. Skyrmion lattice in a chiral magnet. Science 323, 915–919 (2009).

    Article  Google Scholar 

  14. Imada, M., Tokura, Y. & Fujimori, A. Metal–insulator transition. Rev. Mod. Phys. 70, 1039–1263 (1998).

    Article  CAS  Google Scholar 

  15. Hsieh, D. et al. Observation of a metal-to-insulator transition with both Mott–Hubbard and Slater characteristics in Sr2IrO4 from time-resolved photocarrier dynamics. Phys. Rev. B 86, 035128 (2012).

    Article  Google Scholar 

  16. Fujiyama, S. et al. Weak antiferromagnetism of Jeff = 1/2 band in bilayer iridate Sr3Ir2O7 . Phys. Rev. B 86, 174414 (2012).

    Article  Google Scholar 

  17. Arita, R. et al. Ab initio studies on the interplay between spin–orbit interaction and coulomb correlation in Sr2IrO4 and Ba2IrO4 . Phys. Rev. Lett. 108, 086403–086406 (2012).

    Article  CAS  Google Scholar 

  18. Cao, G. et al. Anomalous magnetic and transport behavior in the magnetic insulator Sr3Ir2O7 . Phys. Rev. B 66, 214412–214418 (2002).

    Article  Google Scholar 

  19. Dhital, C. et al. Spin ordering and electronic texture in the bilayer iridate Sr3Ir2O7 . Phys. Rev. B 86, 100401–100404 (2012).

    Article  Google Scholar 

  20. Wang, Q. et al. Dimensionality controlled Mott transition and correlation effects in single- and bi-layer perovskite iridates. Preprint at (2012).

  21. Wojek, B. M. et al. The Jeff = 1/2 Mott insulator Sr3Ir2O7 studied by angle-resolved photoemission spectroscopy. J. Phys.: Condens. Matter 24, 415602 (2012).

    CAS  Google Scholar 

  22. Dagotto, E. Complexity in strongly correlated electronic systems. Science 309, 257–262 (2005).

    Article  CAS  Google Scholar 

  23. Pan, S. H. et al. Microscopic electronic inhomogeneity in the high- Tc superconductor Bi2Sr2CaCu2O8+x . Nature 413, 282–285 (2001).

    Article  CAS  Google Scholar 

  24. Lee, J. et al. Heavy d-electron quasiparticle interference and real-space electronic structure of Sr3Ru2O7 . Nature Phys. 5, 800–804 (2009).

    Article  CAS  Google Scholar 

  25. Iwaya, K. et al. Local tunneling spectroscopy across a metamagnetic critical point in the bi-layer ruthenate Sr3Ru2O7 . Phys. Rev. Lett. 99, 057208–057211 (2007).

    Article  CAS  Google Scholar 

  26. Subramanian, M. A., Crawford, M. K. & Harlow, R. L. Single crystal structure determination of double layered strontium iridium oxide Sr3Ir2O7 . Mater. Res. Bull. 29, 645–650 (1994).

    Article  CAS  Google Scholar 

  27. Korneta, O. B. et al. Electron-doped Sr2IrO4−δ (0≤δ≤0.04): Evolution of a disordered Jeff = 1/2 Mott insulator into an exotic metallic state. Phys. Rev. B 82, 115117 (2010).

    Article  Google Scholar 

  28. Tokura, Y., Takagi, H. & Uchida, S. A superconducting copper oxide compound with electrons as the charge carriers. Nature 337, 345–347 (1989).

    Article  CAS  Google Scholar 

  29. Ohta, Y., Tohyama, T. & Maekawa, S. Apex oxygen and critical temperature in copper oxide superconductors: Universal correlation with the stability of local singlets. Phys. Rev. B 43, 2968–2982 (1991).

    Article  CAS  Google Scholar 

  30. Pavarini, E. et al. Band-structure trend in hole-doped cuprates and correlation with Tcmax . Phys. Rev. Lett. 87, 047003–047006 (2001).

    Article  CAS  Google Scholar 

  31. Kohsaka, Y. et al. Visualization of the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator. Nature Phys. 8, 534–538 (2012).

    Article  CAS  Google Scholar 

  32. Ye, C. et al. Visualizing the atomic scale electronic structure of the Ca2CuO2Cl2 Mott insulator. Nature Commun. 4, 1365 (2013).

    Article  Google Scholar 

  33. Zhou, S. et al. Electron correlation and Fermi surface topology of NaxCoO2 . Phys. Rev. Lett. 94, 206401–206404 (2005).

    Article  Google Scholar 

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V.M. gratefully acknowledges funding from US NSF-CAREER-0645299 for support of D.W., Y.O. and W.Z. S.D.W. acknowledges NSF DMR-1056625 for support of C.D. and S.K. Z.W. acknowledges the DOE grants: DE-FG02-99ER45747 and DOE DE-SC0002554. T.R.C. and H.T.J. are supported by the National Science Council, Taiwan. H.T.J also thanks NCHC, CINC-NTU and NCTS, Taiwan for technical support. The work at Northeastern University is supported by the US Department of Energy, Office of Science, Basic Energy Sciences contract DE-FG02-07ER46352, and benefited from Northeastern University’s Advanced Scientific Computation Center (ASCC), theory support at the Advanced Light Source, Berkeley and the allocation of supercomputer time at NERSC through DOE grant number DE-AC02-05CH11231.

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Y.O. and V.M. designed the experiments. Y.O., M.P., W.Z. and D.W. participated in the the experiments. V.M., Y.O., S.D.W., Z.W. and D.W. wrote the paper. C.D. and S.K. made single-crystal samples. Z.W., H-T.J., T-R.C., H.L. and A.B. carried out the theoretical calculations.

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Correspondence to Vidya Madhavan.

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Okada, Y., Walkup, D., Lin, H. et al. Imaging the evolution of metallic states in a correlated iridate. Nature Mater 12, 707–713 (2013).

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