# Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4

## Abstract

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity1,2,3,4. Recently, photo-excitation has been used to induce similarly exotic states transiently5,6,7. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

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## Acknowledgements

The X-ray scattering work by M.P.M.D., Y.C., V.T. and X.M.C. was supported by the US Department of Energy Basic Energy Sciences Division of Materials Science and Engineering. X.L. acknowledges financial support from MOST (No. 2015CB921302) and CAS (Grant No: XDB07020200) of China. P.J. acknowledges support by Laboratory Directed Research and Development (LDRD) Program 12-007 (Complex Modeling). J.K., D.C. and A.H.S. were supported by the US Department of Energy under Contract No. DE-AC02-06CH11357. S.W. acknowledges financial support from Spanish MINECO (Severo Ochoa grant SEV-2015-0522), Ramon y Cajal programme RYC-2013-14838, Marie Curie Career Integration Grant PCIG12-GA-2013-618487 and Fundació Privada Cellex. J.L. is sponsored by the Science Alliance Joint Directed Research and Development Program at the University of Tennessee. Work in London was supported by the EPSRC. The magnetic Bragg peak measurements were performed at the BL3 of SACLA with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2014B8018). This research made use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, which is a DOE Office of Science User Facility, under Contract No. DE-AC02-76SF00515.

## Author information

J.P.H., X.L., M.P.M.D. and M.F. initiated and planned the project. M.P.M.D., Y.C., X.L., S.W., D.Z., R.M., V.T., X.M.C., J.G.V., D.C., J.K., A.H.S., P.J., R.A.-M., J.M.G., A.R., J.R., M.S., S.S., M.K., H.L., L.P., S.O., T.K., M.Y., Y.T., T.T., L.H., C.-L.C., D.F.M., M.F. and J.P.H. prepared for and performed the experiments. M.P.M.D., Y.C., X.L., S.W., M.F., D.F.M. and J.P.H. analysed and interpreted the data. J.L., C.R.S. and B.J.K. prepared the samples. M.P.M.D. and Y.C. wrote the paper with contributions from X.L., S.W., D.F.M., M.F. and J.P.H.

Correspondence to M. P. M. Dean or Y. Cao or X. Liu.

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### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

Supplementary Information (PDF 436 kb)

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Dean, M., Cao, Y., Liu, X. et al. Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4. Nature Mater 15, 601–605 (2016) doi:10.1038/nmat4641

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https://doi.org/10.1038/nmat4641

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