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

• DOI: 10.1038/s41567-022-01848-w
• Publication Date: 2022-12-22T17:04:23Z
• Authors: Allan S. Johnson; Daniel Perez-Salinas; Khalid M. Siddiqui; Sungwon Kim; Sungwook Choi; Klara Volckaert; Paulina E. Majchrzak; Søren Ulstrup; Naman Agarwal; Kent Hallman; Richard F. Haglund; Christian M. Günther; Bastian Pfau; Stefan Eisebitt; Dirk Backes; Francesco Maccher...; Ann Fitzpatrick; Sarnjeet S. Dhesi; Pierluigi Gargiani; Manuel Valvidares; Nongnuch Artrith; Frank de Groot; Hyeongi Choi; Dogeun Jang; Abhishek Katoch; Soonnam Kwon; Sang Han Park; Hyunjung Kim; Simon E. Wall
• Keywords: Condensed Matter - Materials Science; Condensed Matter - Mesoscale and Nanoscale Physics; Strongly Correlated Electrons (cond-mat.str-el); General Physics and Astronomy; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; 530 Physik; 01 natural sciences; phase transitions and critical phenomena; Condensed Matter - Strongly Correlated Electrons; electronic devices; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); X-rays; 0103 physical sciences; electronic properties and materials

AbstractUsing 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.