The recent combination of attosecond technology and tabletop X-ray spectroscopy in the soft X-ray range has heralded a new era of ultrafast science and opened doors to better understanding quantum materials, light harvesting devices, and ultrafast electronics.

Buades et al. presents the state of the field and the first case study of using such fast X-ray spectroscopy. The authors studied a sample of titanium disulfide, a quantum material with potential applications in batteries. To achieve attosecond resolution, they used high harmonic generation, which up-converts visible and infrared photos to ultraviolet and soft X-rays.

Combined with X-ray absorption near-edge spectroscopy, the authors were able to probe the fine structure of an absorption edge in real time and isolate the orbitals’ spectral contributions. The results showed titanium disulfide could be a promising candidate for petahertz field-effect devices.

Previously, only hundreds of femtosecond time resolution have been possible and required massive multibillion-dollar synchrotrons. While other more accessible techniques exist, such as Raman spectroscopy and photoemission spectroscopy, none could singlehandedly provide the clean real-time broadband observations.

“Ultimately, this technique will not replace all the other techniques, but for the first time, it’s giving us a unifying picture,” said author Jens Biegert.

The authors noted that in addition to measuring real time optoelectrical properties, the technique could also be used to study the exact interaction of electrons, holes, and lattice modes. This could help answer long-standing questions about phase transitions and superconductivity. Additionally, the method could be applied to any number of systems including gases, liquids, solids, and amorphous systems.

Source: “Attosecond state-resolved carrier motion in quantum materials probed by soft x-ray XANES,” by Bárbara Buades, Antonio Picón, Emma Berger, Iker León, Nicola Di Palo, Seth L. Cousin, Caterina Cocchi, Eric Pellegrin, Javier Herrero Martin, Samuel Mañas-Valero, Eugenio Coronado, Thomas Danz, Claudia Drax, Mitsuharu Uemoto, Kazuhiro Yabana, Martin Schultze, Simon Wall, Michael Zürch, and Jens Biegert, Applied Physics Review (2021). The article can be accessed at