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A charge density wave-like instability in a doped spin–orbit-assisted weak Mott insulator

Abstract

Layered perovskite iridates realize a rare class of Mott insulators that are predicted to be strongly spin–orbit coupled analogues of the parent state of cuprate high-temperature superconductors1,2. Recent discoveries of pseudogap3,4,5, magnetic multipolar ordered6 and possible d-wave superconducting phases7,8 in doped Sr2IrO4 have reinforced this analogy among the single layer variants. However, unlike the bilayer cuprates9, no electronic instabilities have been reported in the doped bilayer iridate Sr3Ir2O7. Here we show that Sr3Ir2O7 realizes a weak Mott state with no cuprate analogue9 by using ultrafast time-resolved optical reflectivity to uncover an intimate connection between its insulating gap and antiferromagnetism. However, we detect a subtle charge density wave-like Fermi surface instability in metallic electron doped Sr3Ir2O7 at temperatures (TDW) close to 200 K via the coherent oscillations of its collective modes, which is reminiscent of that observed in cuprates10,11. The absence of any signatures of a new spatial periodicity below TDW from diffraction12, scanning tunnelling12 and photoemission13,14 based probes suggests an unconventional and possibly short-ranged nature of this density wave order.

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Figure 1: Temperature-dependent reflectivity transients of Sr3Ir2O7 (x = 0).
Figure 2: Doping-dependent reflectivity transients of (Sr1−xLax)3Ir2O7.
Figure 3: Coherent oscillations of an electronic order parameter.
Figure 4: Reflectivity transients of insulating (Sr1−xCax)3Ir2O7.

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Acknowledgements

We thank V. Madhavan and Z. Wang for providing scanning tunnelling microscopy data and analysis on (Sr1−xLax)3Ir2O7 samples and for helpful discussions. This work is supported by a GIST-Caltech Collaboration Grant and by ARO Grant W911NF-13-1-0059. Instrumentation was partially supported by ARO DURIP Award W911NF-13-1-0293. D.H. acknowledges funding provided by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center (PHY-1125565) with support of the Gordon and Betty Moore Foundation through Grant GBMF1250. S.D.W. acknowledges support under NSF award No. DMR-1505549 as well as partial support from the MRSEC Program of the National Science Foundation under Award No. DMR 1121053 (T.H.).

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H.C., L.Z. and D.H. planned the experiment. H.C. performed the measurements. H.C., A.d.l.T., D.H. and L.Z. analysed the data. T.H. and S.D.W. prepared and characterized the samples and performed RIXS measurements. H.C. and D.H. wrote the manuscript.

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Correspondence to D. Hsieh.

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The authors declare no competing financial interests.

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Chu, H., Zhao, L., de la Torre, A. et al. A charge density wave-like instability in a doped spin–orbit-assisted weak Mott insulator. Nature Mater 16, 200–203 (2017). https://doi.org/10.1038/nmat4836

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