Abstract
Photo-excited quantum materials can be driven into thermally inaccessible metastable states that exhibit structural, charge, spin, topological and superconducting orders. Metastable states typically emerge on timescales set by the intrinsic electronic and phononic energy scales, ranging from femtoseconds to picoseconds, and can persist for weeks. Therefore, studies have primarily focused on ultrafast or quasi-static limits, leaving the intermediate time window less explored. Here we reveal a metastable state with broken glide-plane symmetry in photo-doped Ca2RuO4 using time-resolved optical second-harmonic generation and birefringence measurements. We find that the metastable state appears long after intralayer antiferromagnetic order has melted and photo-carriers have recombined. Its properties are distinct from all known states in the equilibrium phase diagram and are consistent with intralayer ferromagnetic order. Furthermore, model Hamiltonian calculations reveal that a non-thermal trajectory to this state can be accessed via photo-doping. Our results expand the search space for out-of-equilibrium electronic matter to metastable states emerging at intermediate timescales.
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Data availability
Data supporting findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.
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Acknowledgements
We thank E. Demler, A. Millis, G. Khaliullin and W. Liu for useful discussions. D.H. acknowledges support for instrumentation and theory from the Institute for Quantum Information and Matter (IQIM), an NSF Physics Frontiers Center (grant number PHY-2317110). Optical spectroscopy measurements were funded in part by the Gordon and Betty Moore Foundation through grant number GBMF11564 to Caltech to support the work of D.H. G.R. acknowledges the support of the Simons Foundation, ARO MURI grant number W911NF-16-1- 0361 and the Institute of Quantum Information and Matter (grant number PHY-2317110). X.L. acknowledges support from the Caltech Postdoctoral Prize Fellowship and the Singapore National Research Foundation under award number NRF-NRFF16-2024-0008. G.C. acknowledges support from the National Science Foundation via grant number DMR 2204811. I.E. acknowledges support from the Simons Foundation and the IQIM.
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X.L. and D.H. conceived the experiment. X.L., Y.H. and C.B. performed the RA-SHG and B-field-induced SHG experiments. X.L. and Y.L. performed birefringence polarimetry experiments. H.N. contributed to interpreting the lattice SHG data. J.-Y.S. and K.S. developed the RA-SHG set-up and adapted it for magnetic SHG measurements. K.S. made the magnetic rotator. I.E., G.R. and X.L. developed the theoretical interpretation. H.Z. and G.C. synthesized and characterized the samples. D.H. supervised the project. X.L. and D.H. wrote the manuscript with input from all authors.
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Li, X., Esin, I., Han, Y. et al. Time-hidden magnetic order in a multi-orbital Mott insulator. Nat. Phys. 21, 451–457 (2025). https://doi.org/10.1038/s41567-024-02752-1
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DOI: https://doi.org/10.1038/s41567-024-02752-1
