Articles

2026

• Thermodynamics of the ultrafast phase transition of vanadium dioxide
  Shreya Bagchi, Ernest Pastor, José Santiso, Allan S. Johnson and Simon Wall
  arXiv preprint arXiv:2603.04600 (2026)
• Non-linear X-ray Coherent Diffractive Imaging
  Arnab Sarkar and Allan S. Johnson
  arXiv preprint arXiv:2512.15457 (2026)

2025

• Electron coherent phonon coupling in PrCaMnO measured with ultrafast broadband spectroscopy
  Emmanuel B Amuah, Khalid M Siddiqui, Maurizio Monti, Daniel Pérez-Salinas, Hanna Strojecka, Thomas H Meyland, Allan S Johnson and Simon E Wall
  arXiv preprint arXiv:2508.14834 (2025)
• Decoupled few-femtosecond phase transitions in vanadium dioxide
  Christian Brahms, Lin Zhang, Xiao Shen, Utso Bhattacharya, Maria Recasens, Johann Osmond, Tobias Grass, Ravindra W Chhajlany, Kent A Hallman, Richard F Haglund, Sokrates T Pantelides, Maciej Lewenstein, John C Travers, Allan S Johnson
  Nature Communications 16 (1), 3714 (2025)
• Tensor network study of the light-induced phase transitions in vanadium dioxide.
  Lin Zhang, Utso Bhattacharya, Maria Recasens, Tobias Grass, Ravindra W Chhajlany, Maciej Lewenstein, Allan S Johnson.
  npj Quantum Materials 10, 32 (2025) https://doi.org/10.1038/s41535-025-00751-w
• M Recasens, V Kasper, M Lewenstein and AS Johnson. Chirped pulse control over the melting of superconductors. Physical Review B 111, 064513 (2025). https://doi.org/10.1103/PhysRevB.111.064513

2024

• Coherent X-ray imaging of stochastic dynamics.
  A Sarkar and AS Johnson.
  Materials Advances 5, 6378-6387(2024). https://doi.org/10.1039/D4MA00154K
• All-optical seeding of a light-induced phase transition with correlated disorder.
  Allan S Johnson, Ernest Pastor, Sergi Batlle-Porro, Hind Benzidi, Tetsuo Katayama, Gilberto A de la Peña Muñoz, Viktor Krapivin, Sunam Kim, Núria López, Mariano Trigo, Simon E Wall.
  Nature Physics 20, 970-975 (2024). https://doi.org/10.1038/s41567-024-02474-4
• Determination and correction of spectral phase from principal component analysis of coherent phonons.
  Emmanuel B. Amuah, Khalid M. Siddiqui, Maurizio Monti, Allan S. Johnson, and Simon E. Wall.
  Optics Express Vol. 32, Issue 3, pp. 3817-3825 (2024). doi:10.1364/OE.514141

2023

• Ultrafast lattice disordering can be accelerated by electronic collisional forces.
  Gilberto A de la Peña Muñoz, Alfredo A Correa, Shan Yang, Olivier Delaire, Yijing Huang, Allan S Johnson, Tetsuo Katayama, Viktor Krapivin, Ernest Pastor, David A Reis, Samuel Teitelbaum, Luciana Vidas, Simon Wall, Mariano Trigo.
  Nature Physics (2023) doi:10.1038/s41567-023-02118-z
• Ultrafast X-ray imaging of the light-induced phase transition in VO₂.
  Allan S. Johnson, Daniel Pérez-Salinas, Khalid M. Siddiqui, Sungwon Kim, Sungwook Choi, Klara Volckaert, Paulina E. Majchrzak, Søren Ulstrup, Kent Hallman, Richard F. Haglund Jr., Christian M. Günther, Bastian Pfau, Stefan Eisebitt, Dirk Backes, Francesco Maccherozzi, Ann Fitzpatrick, Sarnjeet Dhesi, Pierluigi Gargiani, Manuel Valvidares, Hyeongi Choi, Dogeun Jang, Abhishek Katoch, Soonnam Kwon, Sang Han Park, Hyunjung Kim, Simon E. Wall.
  Nature Physics 19, 215–220 (2023) doi:10.1038/s41567-022-01848-w.

2022

• Nonthermal breaking of magnetic order via photogenerated spin defects in the spin-orbit coupled insulator Sr3Ir2O7. 
  Ernest Pastor, David Moreno-Mencía, Maurizio Monti, Allan S Johnson, Nina Fleischmann, Cuixiang Wang, Youguo Shi, Xuerong Liu, Daniel G Mazzone, Mark PM Dean, Simon Wall. 
  Physical Review B 105, 064409 (2022) doi:10.1103/PhysRevB.105.064409
• Multi-mode excitation drives disorder during the ultrafast melting of a C4-symmetry-broken phase
  Daniel Perez-Salinas*, Allan S Johnson*, Dharmalingam Prabhakaran, Simon Wall. A. S. Johnson, D. Moreno-Mencía, E. B. Amuah, M. Menghini, J.-P. Locquet, C. Gianetti, E. Pastor, S. E. Wall.
• Ultrafast loss of lattice coherence in the light-induced structural phase transition of V2O3.
  A. S. Johnson, D. Moreno-Mencía, E. B. Amuah, M. Menghini, J.-P. Locquet, C. Gianetti, E. Pastor, S. E. Wall.
  Physical Review Letters 129, 255701 (2022).doi:10.1103/PhysRevLett.129.255701.
• Direct observation of ultrafast exciton localization in an organic semiconductor with soft X-ray transient absorption spectroscopy.
  Douglas Garratt, Lukas Misiekis, David Wood, Esben Witting Larsen, Mary Matthews, Oliver Alexander, Peng Ye, Sebastian Jarosch, Clement Ferchaud, C Strüber, AS Johnson, AA Bakulin, TJ Penfold, JP Marangos. 
  Nature Communications 13 (1), 1-8 (2022).  doi:10.1038/s41467-022-31008-w
• Fermionic Chern insulator from twisted light with linear polarization.
  Utso Bhattacharya, Swati Chaudhary, Tobias Grass, Allan S Johnson, Simon Wall and Maciej Lewenstein. 
  Physical Review B 105, L081406 (2022) doi:10.1103/PhysRevB.105.L081406