New Approach to Ultrafast Multi-Dimensional Spectroscopy
An international team of researchers from the European XFEL, along with colleagues from the Max-Born Institute in Berlin (partners of OPTOlogic), Universities of Berlin and Hamburg, The University of Tokyo, the Japanese National Institute of Advanced Industrial Science and Technology (AIST), the Dutch Radboud University, Imperial College London, and Hamburg Center for Ultrafast Imaging, have presented new ideas for ultrafast multi-dimensional spectroscopy of strongly correlated solids. This work has now been published in Nature Photonics.
Cartoon view of the key many-body states corresponding to the spectroscopic signal at energies of the LHB, QP and UHB.
The Complexity of Strongly Correlated Solids
“Strongly correlated solids are complex and fascinating quantum systems in which new electronic states often emerge, especially when they interact with light” says Alexander Lichtenstein from Hamburg University and Eu-XFEL. Strongly correlated materials, including high-temperature superconductors, certain types of magnetic materials, and twisted quantum materials, challenge our fundamental understanding of the microcosm. Moreover, they offer opportunities for many exciting applications ranging from materials science to information processing to medicine. For example, superconductors are used by MRI scanners. Understanding the hierarchy and interplay of the diverse electronic states arising in strongly correlated materials is very important.
Challenges of Studying Phase Transitions
At the same time, these materials challenge our experimental and theoretical tools because transformations between these states often involve phase transitions. Phase transitions do not develop smoothly from one stage to the next but may occur suddenly and quickly, particularly when light interacts with the material. How do pathways of charge and energy flow during such a transition? How quickly does it occur? Can light control it and sculpt the electron correlations? Can light bring the material into a state that it wouldn’t find itself in under usual circumstances? Powerful and sensitive devices like X-ray lasers such as the European XFEL in Schenefeld near Hamburg, and modern optical tools of attosecond science (1 attosecond = 10^-18 sec), address these types of questions.
A New Approach to Monitor Ultrafast Charge Motion
In their work, the international team now presents a completely new approach that makes it possible to monitor and decipher the ultrafast charge motion triggered by a short laser pulse illuminating a strongly correlated system. They have developed a variant of ultrafast multi-dimensional spectroscopy, taking advantage of the attosecond control of how multiple colors of light add to form an ultrashort laser pulse. The sub-cycle temporal resolution offered by this spectroscopy shows the complex interplay between the different electronic configurations and demonstrates that a phase transition from a metallic state to an insulating state can take place within less than a femtosecond – i.e. in less than one quadrillionth of a second.
New Tools for Investigating Ultrafast Processes
“Our results open up a way of investigating and specifically influencing ultrafast processes in strongly correlated materials that goes beyond previous methods” says Olga Smirnova from the Max-Born Institute and Berlin TU, awardee of the Mildred Dresselhaus prize of the Hamburg Centre for Ultrafast Imaging, “we have thus developed a key tool for accessing new ultrafast phenomena in correlated solids”.
Reference: Sub-cycle multidimensional spectroscopy of strongly correlated materials, V. N. Valmispild, E. Gorelov, M. Eckstein, A. I. Lichtenstein, H. Aoki, M. I. Katsnelson, M. Yu. Ivanov & O. Smirnova, Nature Photonics (2024)
