Ultrafast X-ray imaging of the light-induced phase transition in VO2

• Published in: Nature physics Vol. 19; no. 2; pp. 215 - 220
• Main Authors: Johnson, Allan S., Perez-Salinas, Daniel, Siddiqui, Khalid M., Kim, Sungwon, Choi, Sungwook, Volckaert, Klara, Majchrzak, Paulina E., Ulstrup, Søren, Agarwal, Naman, Hallman, Kent, Haglund, Richard F., Günther, Christian M., Pfau, Bastian, Eisebitt, Stefan, Backes, Dirk, Maccherozzi, Francesco, Fitzpatrick, Ann, Dhesi, Sarnjeet S., Gargiani, Pierluigi, Valvidares, Manuel, Artrith, Nongnuch, de Groot, Frank, Choi, Hyeongi, Jang, Dogeun, Katoch, Abhishek, Kwon, Soonnam, Park, Sang Han, Kim, Hyunjung, Wall, Simon E.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.02.2023; Nature Publishing Group
• Subjects: 639/301/1005/1007; 639/301/119/2795; 639/301/119/995; 639/624/400/1106; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Heterogeneity; Mathematical and Computational Physics; Metal-insulator transition; Molecular; Optical and Plasma Physics; Phase transitions; Phases; Physics; Physics and Astronomy; Theoretical; Vanadium; Vanadium dioxide; Vanadium oxides; X ray imagery
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-022-01848-w

Using light to control transient phases in quantum materials is an emerging route to engineer new properties and functionality, with both thermal and non-thermal phases observed out of equilibrium. Transient phases are expected to be heterogeneous, either through photo-generated domain growth or by generating topological defects, and this impacts the dynamics of the system. However, this nanoscale heterogeneity has not been directly observed. Here we use time- and spectrally resolved coherent X-ray imaging to track the prototypical light-induced insulator-to-metal phase transition in vanadium dioxide on the nanoscale with femtosecond time resolution. We show that the early-time dynamics are independent of the initial spatial heterogeneity and observe a 200 fs switch to the metallic phase. A heterogeneous response emerges only after hundreds of picoseconds. Through spectroscopic imaging, we reveal that the transient metallic phase is a highly orthorhombically strained rutile metallic phase, an interpretation that is in contrast to those based on spatially averaged probes. Our results demonstrate the critical importance of spatially and spectrally resolved measurements for understanding and interpreting the transient phases of quantum materials. The intermediate states in photo-excited phase transitions are expected to be inhomogeneous. However, ultrafast X-ray imaging shows the early part of the metal–insulator transition in VO 2 is homogeneous but then becomes heterogeneous.