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Picosecond volume expansion drives a later-time insulator–metal transition in a nano-textured Mott insulator

Nature Physics (2024)Cite this article

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Abstract

There is significant technological interest in developing ever faster switching between different electronic and magnetic states of matter. Manipulating properties at terahertz rates requires accessing the intrinsic timescales of both electrons and associated phonons, which is possible with short-pulse photoexcitation. However, in many Mott insulators, the electronic transition is accompanied by the nucleation and growth of percolating domains of the changed lattice structure, leading to empirical timescales dominated by slowly coarsening dynamics. Here we use time-resolved X-ray diffraction and reflectivity measurements to show that the photoinduced insulator-to-metal transition in an epitaxially strained Mott insulating thin film occurs without observable domain formation and coarsening effects, allowing the study of the intrinsic electronic and lattice dynamics. Above a fluence threshold, the initial electronic excitation drives a fast lattice rearrangement, which is followed by a slower electronic evolution into a metastable nonequilibrium state. Microscopic model calculations based on time-dependent dynamical mean-field theory and semiclassical lattice dynamics explain the threshold behaviour and elucidate the delayed onset of the electronic phase transition. This work highlights the importance of combined electronic and structural studies in unravelling the physics of dynamic transitions and the timescales of photoinduced processes.

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Fig. 1: Photoinduced structural change and insulator-to-metal transition.
Fig. 2: Photoinduced structural rearrangements of the Ca2RuO4 unit cell.
Fig. 3: Results from time-dependent DMFT and quantitative Landau theory.
Fig. 4: Dynamics in the nano-texture in the strained Ca2RuO4 thin film.

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Data availability

The time-resolved X-ray reciprocal space mapping data presented in this work are available for download at Zenodo (https://doi.org/10.5281/zenodo.10373577).

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Acknowledgements

The work was primarily supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (Contract No. DE-SC0019414 for X-ray experiments and interpretation to A.V., O.G., J.P.R., J.Z.K, G.K, K.M.S. and A.S., for thin-film synthesis to H.N. and N.S., for DFT calculations to J.Z.K, G.K. and N.A.B. and for high-frequency reflectivity to R.R. and J.W.H.). A.J.M. acknowledges support from the US Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Scientific Discovery through the Advanced Computing programme (Award No. DE-SC0022088). This research was funded in part by the Gordon and Betty Moore Foundation’s EPiQS Initiative (Grant Nos. GBMF3850 and GBMF9073 to Cornell University). Sample preparation was, in part, facilitated by the Cornell NanoScale Facility, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (NSF; Grant No. NNCI-2025233). This work was also supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (Contract No. DE-SC0001805 for temperature-dependent XRD to E.L. and O.G.S.). H.P., V.A.S. and J.W.F. acknowledge support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences (Award No. DE-SC-0012375 for studying complex-oxide heterostructures with X-ray scattering). The X-ray free-electron laser experiments were performed at beamline 3 at the SPring-8 Angstrom Compact Free-electron Laser with the approval of the Japan Synchrotron Radiation Research Institute (Proposal No. 2019A8084). D.G. is supported by the Slovenian Research Agency (Programmes J1-2455, P1-0044 and MN-0016-106). K.K., V.R. and R.D.A are supported by the NSF (Grant No. DMR-1810310). The calculations were performed using a software library developed by M. Eckstein and H.U.R. Strand. The Flatiron Institute is a division of the Simons Foundation. We thank B. Gregory and Z. Shao for measuring the resistivity.

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Authors and Affiliations

  1. Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA

    Anita Verma, Oleg Yu. Gorobtsov, Guru Khalsa, Hari P. Nair, Yifei Sun, Ryan Bouck, Nathaniel Schreiber, Nicole A. Benedek, Darrell G. Schlom & Andrej Singer

  2. Jozef Stefan Institute, Ljubljana, Slovenia

    Denis Golež

  3. Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia

    Denis Golež

  4. Department of Physics, University of California San Diego, La Jolla, CA, USA

    Kelson Kaj, Erik Lamb, Varun Ramaprasad, Oleg G. Shpyrko & Richard D. Averitt

  5. Materials Department, University of California, Santa Barbara, CA, USA

    Ryan Russell & John W. Harter

  6. School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA

    Jeffrey Z. Kaaret

  7. Physics Department, Cornell University, Ithaca, NY, USA

    Jacob P. Ruf & Kyle M. Shen

  8. RIKEN SPring-8 Center, Hyogo, Japan

    Yuya Kubota & Tadashi Togashi

  9. Japan Synchrotron Radiation Research Institute, Hyogo, Japan

    Yuya Kubota & Tadashi Togashi

  10. Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA, USA

    Vladimir A. Stoica & Hari Padmanabhan

  11. X-ray Science Division, Argonne National Laboratory, Argonne, IL, USA

    John W. Freeland

  12. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY, USA

    Darrell G. Schlom & Kyle M. Shen

  13. Leibniz-Institut für Kristallzüchtung, Berlin, Germany

    Darrell G. Schlom

  14. Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA

    Andrew J. Millis

  15. Department of Physics, Columbia University, New York, NY, USA

    Andrew J. Millis

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  1. Anita Verma
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Contributions

A.S., D.G.S. and K.M.S. conceived the idea. O.Y.G., Y.S., R.B., Y.K. and T.T. conducted the time-resolved X-ray experiments. A.V. analysed the time-resolved X-ray data with help from J.Z.K, G.K. and A.S. D.G. and A.J.M. performed the time-resolved DMFT calculations. H.N., N.S. and J.P.R. synthesized and characterized the films with advice from K.M.S. and D.G.S. J.Z.K., G.K. and N.A.B. performed the DFT calculations. K.K., V.R. and R.D.A. conducted the low-frequency reflectivity experiments. E.L. and O.G.S. collected the temperature-dependent XRD data. V.A.S., H.P. and J.W.F. assisted in the interpretation of the X-ray data. R.R. and J.W.H. conducted the high-frequency reflectivity experiments. A.V., D.G., A.J.M. and A.S. wrote the paper with comments from all co-authors.

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Correspondence to Andrej Singer.

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Verma, A., Golež, D., Gorobtsov, O.Y. et al. Picosecond volume expansion drives a later-time insulator–metal transition in a nano-textured Mott insulator. Nat. Phys. (2024). https://doi.org/10.1038/s41567-024-02396-1

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