Ultrafast
New transient states via photo-excitation
We have been pioneering the application of RIXS to transient states created by ultrafast laser pulses, using x-ray free electron lasers (XFELs) as the x-ray source. Time-resolved RIXS (trRIXS) is uniquely positioned to access momentum-resolved charge, spin, and orbital excitations of driven quantum materials—capabilities beyond the reach of optical probes or ultrafast diffraction. We have used trRIXS to track the ultrafast dynamics of magnetic excitations, charge order melting, and the onset of photo-induced electronic states. Looking forward, we are pursuing Floquet-engineered magnetic phases, the search for photoinduced superconductivity, and novel forms of electronic metastability and non-equilibrium condensation.
References
2026
- Light-Induced Charge Order Mode in a Metastable Cuprate LadderHari Padma, Prakash Sharma, Sophia F. R. TenHuisen, Filippo Glerean, Antoine Roll, Pan Zhou, Sarbajaya Kundu, Arnau Romaguera, Elizabeth Skoropata, Hiroki Ueda, Biaolong Liu, Eugenio Paris, Yu Wang, Seng Huat Lee, Zhiqiang Mao, Mark P. M. Dean, Edwin W. Huang, Elia Razzoli, Yao Wang, and Matteo MitranoPhys. Rev. Lett. 136, 196501 (2026)
We report the observation of an emergent charge order mode in the optically-excited cuprate ladder Sr₁₄Cu₂₄O₄₁. Near-infrared light in the ladder plane drives a symmetry-protected electronic metastable state together with a partial melting of the equilibrium charge order. Our time-resolved resonant inelastic x-ray scattering measurements at the upper Hubbard band reveal a gapless collective excitation dispersing from the charge-order wavevector up to 0.8 eV with a slope on the order of the quasiparticle velocity. These findings reveal a regime where correlated carriers acquire itinerant character at finite momentum, and charge order becomes dynamically fluctuating, offering a platform to explore light-induced pairing instabilities.
@article{padma2026light, title = {Light-Induced Charge Order Mode in a Metastable Cuprate Ladder}, author = {Padma, Hari and Sharma, Prakash and TenHuisen, Sophia F. R. and Glerean, Filippo and Roll, Antoine and Zhou, Pan and Kundu, Sarbajaya and Romaguera, Arnau and Skoropata, Elizabeth and Ueda, Hiroki and Liu, Biaolong and Paris, Eugenio and Wang, Yu and Lee, Seng Huat and Mao, Zhiqiang and Dean, Mark P. M. and Huang, Edwin W. and Razzoli, Elia and Wang, Yao and Mitrano, Matteo}, journal = {Phys. Rev. Lett.}, volume = {136}, issue = {19}, pages = {196501}, numpages = {9}, year = {2026}, month = may, publisher = {American Physical Society}, doi = {10.1103/wdcf-jly6}, url = {https://link.aps.org/doi/10.1103/wdcf-jly6} } - Quantum control of Hubbard excitonsDenitsa R. Baykusheva, Deven Carmichael, Clara S. Weber, I-Te Lu, Filippo Glerean, Tepie Meng, Pedro B. M. De Oliveira, Christopher C. Homes, Igor A. Zaliznyak, G. D. Gu, Mark P. M. Dean, Angel Rubio, Dante M. Kennes, Martin Claassen, and Matteo MitranoNature Materials 136, 196501 (2026)
Quantum control of the many-body wavefunction is a central challenge in quantum materials research, as it could yield a precise control knob to manipulate emergent phenomena. Floquet engineering, the coherent dressing of quantum states with periodic non-resonant optical fields, has become an important strategy for quantum control. Most applications to solid-state systems have targeted weakly interacting or single-ion states, leaving the manipulation of many-body wavefunctions largely unexplored. Here we use Floquet engineering to achieve quantum control of a strongly correlated Hubbard exciton in the one-dimensional Mott insulator Sr2CuO3. A non-resonant mid-infrared optical field coherently dresses the exciton wavefunction, driving its rotation between bright and dark states. We use resonant third-harmonic generation to quantify ultrafast \pi/2 rotations on the Bloch sphere spanned by these exciton states. Our work advances the quest towards programmable control of correlated states and exciton-based quantum sensing.
@article{baykusheva2026quantum, author = {Baykusheva, Denitsa R. and Carmichael, Deven and Weber, Clara S. and Lu, I-Te and Glerean, Filippo and Meng, Tepie and De Oliveira, Pedro B. M. and Homes, Christopher C. and Zaliznyak, Igor A. and Gu, G. D. and Dean, Mark P. M. and Rubio, Angel and Kennes, Dante M. and Claassen, Martin and Mitrano, Matteo}, title = {Quantum control of Hubbard excitons}, journal = {Nature Materials}, year = {2026}, month = mar, day = {09}, issn = {1476-4660}, doi = {10.1038/s41563-026-02517-6}, url = {https://doi.org/10.1038/s41563-026-02517-6} }
2025
- Symmetry-protected electronic metastability in an optically driven cuprate ladderHari Padma, Filippo Glerean, Sophia F. R. TenHuisen, Zecheng Shen, Haoxin Wang, Luogen Xu, Joshua D. Elliott, Christopher C. Homes, Elizabeth Skoropata, Hiroki Ueda, Biaolong Liu, Eugenio Paris, Arnau Romaguera, Byungjune Lee, Wei He, Yu Wang, Seng Huat Lee, Hyeongi Choi, Sang-Youn Park, Zhiqiang Mao, Matteo Calandra, Hoyoung Jang, Elia Razzoli, Mark P. M. Dean, Yao Wang, and Matteo MitranoNature Materials 136, 196501 (2025)
Optically excited quantum materials exhibit non-equilibrium states with remarkable emergent properties, but these phenomena are usually transient, decaying on picosecond timescales and limiting practical applications. Advancing the design and control of non-equilibrium phases requires the development of targeted strategies to achieve long-lived, metastable phases. Here we report the discovery of symmetry-protected electronic metastability in the model cuprate ladder Sr14Cu24O41. Using femtosecond resonant X-ray scattering and spectroscopy, we show that this metastability is driven by a transfer of holes from chain-like charge reservoirs into the ladders. This ultrafast charge redistribution arises from the optical dressing and activation of a hopping pathway that is forbidden by symmetry at equilibrium. Relaxation back to the ground state is, hence, suppressed after the pump coherence dissipates. Our findings highlight how dressing materials with electromagnetic fields can dynamically activate terms in the electronic Hamiltonian, and provide a rational design strategy for non-equilibrium phases of matter.
@article{padma2025symmetry, author = {Padma, Hari and Glerean, Filippo and TenHuisen, Sophia F. R. and Shen, Zecheng and Wang, Haoxin and Xu, Luogen and Elliott, Joshua D. and Homes, Christopher C. and Skoropata, Elizabeth and Ueda, Hiroki and Liu, Biaolong and Paris, Eugenio and Romaguera, Arnau and Lee, Byungjune and He, Wei and Wang, Yu and Lee, Seng Huat and Choi, Hyeongi and Park, Sang-Youn and Mao, Zhiqiang and Calandra, Matteo and Jang, Hoyoung and Razzoli, Elia and Dean, Mark P. M. and Wang, Yao and Mitrano, Matteo}, title = {Symmetry-protected electronic metastability in an optically driven cuprate ladder}, journal = {Nature Materials}, year = {2025}, month = jun, day = {03}, issn = {1476-4660}, doi = {10.1038/s41563-025-02254-2}, url = {https://doi.org/10.1038/s41563-025-02254-2} } - Observation of polarization density waves in SrTiO3Gal Orenstein, Viktor Krapivin, Yijing Huang, Zhuquan Zhang, Gilberto Peña Muñoz, Ryan A. Duncan, Quynh Nguyen, Jade Stanton, Samuel Teitelbaum, Hasan Yavas, Takahiro Sato, Matthias C. Hoffmann, Patrick Kramer, Jiahao Zhang, Andrea Cavalleri, Riccardo Comin, Mark P. M. Dean, Ankit S. Disa, Michael Först, Steven L. Johnson, Matteo Mitrano, Andrew M. Rappe, David Reis, Diling Zhu, Keith A. Nelson, and Mariano TrigoNature Physics 21, 961–965 (2025)
The nature of the incipient ferroelectric transition in SrTiO3 has been a long-standing puzzle in condensed matter physics. One explanation involves the competition between ferroelectricity and an instability characterized by the mesoscopic modulation of the polarization. These polarization density waves, which should intensify near the quantum critical point, break local inversion symmetry and are difficult to characterize with conventional X-ray scattering methods. Here we probe inversion symmetry breaking at finite momenta and visualize the instability of the polarization at the nanometre scale in SrTiO3 by combining a femtosecond X-ray free-electron laser with terahertz coherent control methods. We found polar-acoustic collective modes that are soft, particularly at the tens of nanometre scale. These precursor collective excitations provide evidence for the conjectured mesoscopic-modulated phase in SrTiO3.
@article{orenstein2025observation, dimensions = {true}, author = {Orenstein, Gal and Krapivin, Viktor and Huang, Yijing and Zhang, Zhuquan and de la Pe{\~{n}}a Mu{\~{n}}oz, Gilberto and Duncan, Ryan A. and Nguyen, Quynh and Stanton, Jade and Teitelbaum, Samuel and Yavas, Hasan and Sato, Takahiro and Hoffmann, Matthias C. and Kramer, Patrick and Zhang, Jiahao and Cavalleri, Andrea and Comin, Riccardo and Dean, Mark P. M. and Disa, Ankit S. and F{\"o}rst, Michael and Johnson, Steven L. and Mitrano, Matteo and Rappe, Andrew M. and Reis, David and Zhu, Diling and Nelson, Keith A. and Trigo, Mariano}, title = {Observation of polarization density waves in SrTiO<sub>3</sub>}, journal = {Nature Physics}, year = {2025}, month = apr, day = {07}, volume = {21}, pages = {961–965}, issn = {1745-2481}, doi = {10.1038/s41567-025-02874-0}, url = {https://doi.org/10.1038/s41567-025-02874-0} }
2024
- Resolving length-scale-dependent transient disorder through an ultrafast phase transitionJack Griffiths, Ana F. Suzana, Longlong Wu, Samuel D. Marks, Vincent Esposito, Sébastien Boutet, Paul G. Evans, J. F. Mitchell, Mark P. M. Dean, David A. Keen, Ian Robinson, Simon J. L. Billinge, and Emil S. BozinNature Materials 23, 1041–1047 (2024)
Material functionality can be strongly determined by structure extending only over nanoscale distances. The pair distribution function presents an opportunity for structural studies beyond idealized crystal models and to investigate structure over varying length scales. Applying this method with ultrafast time resolution has the potential to similarly disrupt the study of structural dynamics and phase transitions. Here we demonstrate such a measurement of CuIr2S4 optically pumped from its low-temperature Ir-dimerized phase. Dimers are optically suppressed without spatial correlation, generating a structure whose level of disorder strongly depends on the length scale. The redevelopment of structural ordering over tens of picoseconds is directly tracked over both space and time as a transient state is approached. This measurement demonstrates the crucial role of local structure and disorder in non-equilibrium processes as well as the feasibility of accessing this information with state-of-the-art XFEL facilities.
@article{griffiths2024resolving, dimensions = {true}, author = {Griffiths, Jack and Suzana, Ana F. and Wu, Longlong and Marks, Samuel D. and Esposito, Vincent and Boutet, S{\'e}bastien and Evans, Paul G. and Mitchell, J. F. and Dean, Mark P. M. and Keen, David A. and Robinson, Ian and Billinge, Simon J. L. and Bozin, Emil S.}, title = {<strong>Resolving length-scale-dependent transient disorder through an ultrafast phase transition</strong>}, journal = {Nature Materials}, volume = {23}, pages = {1041–1047}, year = {2024}, month = jun, day = {13}, issn = {1476-4660}, doi = {10.1038/s41563-024-01927-8}, url = {https://doi.org/10.1038/s41563-024-01927-8}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=221929&btw=1" target="_blank">BNL Press Release</a>]} }
2022
- Antiferromagnetic excitonic insulator state in Sr3Ir2O7D. G. Mazzone, Y. Shen, H. Suwa, G. Fabbris, J. Yang, S.-S. Zhang, H. Miao, J. Sears, Ke Jia, Y. G. Shi, M. H. Upton, D. M. Casa, X. Liu, Jian Liu, C. D. Batista, and M. P. M. DeanNature Communications 13, 913 (2022)
Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr3Ir2O7. By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges with the electronic continuum in between these high symmetry points and which decays upon heating concurrent with a decrease in the material’s resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr3Ir2O7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulator phase.
@article{mazzone2022antiferromagnetic, dimensions = {true}, author = {Mazzone, D. G. and Shen, Y. and Suwa, H. and Fabbris, G. and Yang, J. and Zhang, S.-S. and Miao, H. and Sears, J. and Jia, Ke and Shi, Y. G. and Upton, M. H. and Casa, D. M. and Liu, X. and Liu, Jian and Batista, C. D. and Dean, M. P. M.}, title = {<strong>Antiferromagnetic excitonic insulator state in Sr<sub>3</sub>Ir<sub>2</sub>O<sub>7</sub></strong>}, journal = {Nature Communications}, year = {2022}, month = feb, day = {17}, volume = {13}, number = {1}, pages = {913}, issn = {2041-1723}, doi = {10.1038/s41467-022-28207-w}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=119438" target="_blank">BNL Press Release</a>]}, note1 = {[<a href="http://www.phys.utk.edu/news/2022/toy-model-magnetism.html" target="_blank">UTK Press Release</a>]}, note2 = {[<a href="https://www.s.u-tokyo.ac.jp/ja/press/2022/7775/" target="_blank">U. Tokyo Press Release</a>]}, url = {https://doi.org/10.1038/s41467-022-28207-w} }
2021
- Laser-induced transient magnons in Sr3Ir2O7 throughout the Brillouin zoneDaniel G. Mazzone, Derek Meyers, Yue Cao, James G. Vale, Cameron D. Dashwood, Youguo Shi, Andrew J. A. James, Neil J. Robinson, Jiaqi Lin, Vivek Thampy, Yoshikazu Tanaka, Allan S. Johnson, Hu Miao, Ruitang Wang, Tadesse A. Assefa, Jungho Kim, Diego Casa, Roman Mankowsky, Diling Zhu, Roberto Alonso-Mori, Sanghoon Song, Hasan Yavas, Tetsuo Katayama, Makina Yabashi, Yuya Kubota, Shigeki Owada, Jian Liu, Junji Yang, Robert M. Konik, Ian K. Robinson, John P. Hill, Desmond F. McMorrow, Michael Först, Simon Wall, Xuerong Liu, and Mark P. M. DeanProceedings of the National Academy of Sciences 118, e2103696118 (2021)
Ultrafast manipulation of magnetic states holds great promise for progress in our understanding of new quantum states and technical applications, but our current knowledge of transient magnetism is very limited. Our work elucidates the nature of transient magnetism in gapped antiferromagnets using Sr3Ir2O7 as a model material. We find that transient magnetic fluctuations are trapped throughout the entire Brillouin zone while remaining present beyond the time that is required to restore the original spin network. The results are interpreted in the context of a spin-bottleneck effect, in which the existence of an explicit magnetic decay channel allows for an efficient thermalization of transient spin waves.Although ultrafast manipulation of magnetism holds great promise for new physical phenomena and applications, targeting specific states is held back by our limited understanding of how magnetic correlations evolve on ultrafast timescales. Using ultrafast resonant inelastic X-ray scattering we demonstrate that femtosecond laser pulses can excite transient magnons at large wavevectors in gapped antiferromagnets and that they persist for several picoseconds, which is opposite to what is observed in nearly gapless magnets. Our work suggests that materials with isotropic magnetic interactions are preferred to achieve rapid manipulation of magnetism.
@article{mazzone2021laser, dimensions = {true}, author = {Mazzone, Daniel G. and Meyers, Derek and Cao, Yue and Vale, James G. and Dashwood, Cameron D. and Shi, Youguo and James, Andrew J. A. and Robinson, Neil J. and Lin, Jiaqi and Thampy, Vivek and Tanaka, Yoshikazu and Johnson, Allan S. and Miao, Hu and Wang, Ruitang and Assefa, Tadesse A. and Kim, Jungho and Casa, Diego and Mankowsky, Roman and Zhu, Diling and Alonso-Mori, Roberto and Song, Sanghoon and Yavas, Hasan and Katayama, Tetsuo and Yabashi, Makina and Kubota, Yuya and Owada, Shigeki and Liu, Jian and Yang, Junji and Konik, Robert M. and Robinson, Ian K. and Hill, John P. and McMorrow, Desmond F. and F{\"o}rst, Michael and Wall, Simon and Liu, Xuerong and Dean, Mark P. M.}, title = {<strong>Laser-induced transient magnons in Sr<sub>3</sub>Ir<sub>2</sub>O<sub>7</sub> throughout the Brillouin zone</strong>}, volume = {118}, number = {22}, elocation-id = {e2103696118}, year = {2021}, doi = {10.1073/pnas.2103696118}, publisher = {National Academy of Sciences}, issn = {0027-8424}, url = {https://www.pnas.org/content/118/22/e2103696118}, eprint = {https://www.pnas.org/content/118/22/e2103696118.full.pdf}, pages = {e2103696118}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=118870" target="_blank">BNL Press Release</a>]}, journal = {Proceedings of the National Academy of Sciences} } - Single-Laser-Pulse-Driven Thermal Limit of the Quasi-Two-Dimensional Magnetic Ordering in Sr2IrO4R. Wang, J. Sun, D. Meyers, J. Q. Lin, J. Yang, G. Li, H. Ding, Anthony D. DiChiara, Y. Cao, J. Liu, M. P. M. Dean, Haidan Wen, and X. LiuPhys. Rev. X 11, 041023 (2021)
Upon femtosecond-laser stimulation, generally materials are expected to recover back to their thermal-equilibrium conditions, with only a few exceptions reported. Here, we demonstrate that deviation from the thermal-equilibrium pathway can be induced in canonical 3D antiferromagnetically (AFM) ordered Sr2IrO4 by a single 100-fs-laser pulse, appearing as losing long-range magnetic correlation along one direction into a glassy condition. We further discover a “critical-threshold ordering” behavior for fluence above approximately 12mJ/cm2, which we show corresponds to the smallest thermodynamically stable c-axis correlation length needed to maintain long-range quasi-two-dimensional AFM order. We suggest that this behavior arises from the crystalline anisotropy of the magnetic-exchange parameters in Sr2IrO4, whose strengths are associated with distinctly different timescales. As a result, they play out very differently in the ultrafast recovery processes, compared with the thermal-equilibrium evolution. Thus, our observations are expected to be relevant to a wide range of problems in the nonequilibrium behavior of low-dimensional magnets and other related ordering phenomena.
@article{wang2021single, dimensions = {true}, title = {Single-Laser-Pulse-Driven Thermal Limit of the Quasi-Two-Dimensional Magnetic Ordering in Sr<sub>2</sub>IrO<sub>4</sub>}, author = {Wang, R. and Sun, J. and Meyers, D. and Lin, J. Q. and Yang, J. and Li, G. and Ding, H. and DiChiara, Anthony D. and Cao, Y. and Liu, J. and Dean, M. P. M. and Wen, Haidan and Liu, X.}, journal = {Phys. Rev. X}, volume = {11}, issue = {4}, pages = {041023}, numpages = {7}, year = {2021}, month = nov, publisher = {American Physical Society}, doi = {10.1103/PhysRevX.11.041023}, url = {https://link.aps.org/doi/10.1103/PhysRevX.11.041023} }
2016
- Ultrafast energy and momentum resolved dynamics of magnetic correlations in photo-doped Mott insulator Sr2IrO4MPM Dean, Yue Cao, X Liu, S Wall, D Zhu, Roman Mankowsky, V Thampy, XM Chen, JG Vale, D Casa, Jungho Kim, A. H. Said, P. Juhas, R. Alonso-Mori, J. M. Glownia, A. Robert, J. Robinson, M. Sikorski, S. Song, M. Kozina, H. Lemke, L. Patthey, S. Owada, T. Katayama, M. Yabashi, Yoshikazu Tanaka, T. Togashi, J. Liu, C. Rayan Serrao, B. J. Kim, L. Huber, C.-L. Chang, D. F. McMorrow, M. Först, and J. P. HillNature Materials 15, 601–605 (2016)
Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and higherature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. 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 Neel 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.
@article{dean2016ultrafast, dimensions = {true}, title = {<strong>Ultrafast energy and momentum resolved dynamics of magnetic correlations in photo-doped Mott insulator Sr<sub>2</sub>IrO<sub>4</sub></strong>}, author = {Dean, MPM and Cao, Yue and Liu, X and Wall, S and Zhu, D and Mankowsky, Roman and Thampy, V and Chen, XM and Vale, JG and Casa, D and Kim, Jungho and Said, A. H. and Juhas, P. and Alonso-Mori, R. and Glownia, J. M. and Robert, A. and Robinson, J. and Sikorski, M. and Song, S. and Kozina, M. and Lemke, H. and Patthey, L. and Owada, S. and Katayama, T. and Yabashi, M. and Tanaka, Yoshikazu and Togashi, T. and Liu, J. and Serrao, C. Rayan and Kim, B. J. and Huber, L. and Chang, C.-L. and McMorrow, D. F. and Först, M. and Hill, J. P.}, journal = {Nature Materials}, note = {[<a href="http://www.nature.com/nmat/journal/v15/n6/full/nmat4647.html" target="_blank">Featured in News and Views</a>]}, note1 = {[<a href="https://www.bnl.gov/newsroom/news.php?a=111836" target="_blank">BNL Press Release</a>]}, volume = {15}, pages = {601--605}, doi = {10.1038/nmat4641}, month = may, year = {2016} }