ICFO researchers’ advances in attosecond soft X-ray spectroscopy have revolutionized materials analysis, particularly in the study of light-matter interactions and many-body dynamics, and have promising implications for future technological applications.
X-ray absorption spectroscopy is a technique sensitive to elemental selectivity and electronic state, and is one of the most widely used analytical techniques to study the composition of materials and substances. Until recently, this method required difficult wavelength scanning and did not provide ultrafast time resolution to study electron dynamics.
Over the past decade, ICFO’s Attoscience and Ultrafast Optics Group, led by ICREA Professor Jens Biegert, has been developing attosecond soft X-ray absorption spectroscopy into new analytical methods that do not require scanning or attosecond time analysis. It was developed as a tool. Solved.[1,2]
A breakthrough in attosecond soft X-ray spectroscopy
Attosecond soft X-ray pulses with durations from 23 as to 165 as and associated coherent soft X-ray bandwidths from 120 to 600 eV[3] The entire electronic structure of a material can be investigated at once.
The combination of temporal resolution to detect electron movement in real time and coherent bandwidth to record where changes occur provides an entirely new and powerful tool for solid-state physics and chemistry.
One of the most fundamentally important processes is the interaction of light and matter. For example, to understand how solar energy is harvested in plants or how solar cells convert sunlight into electricity.
An important aspect of materials science is the prospect that light can change the quantum state and function of materials and substances. Such studies of many-body mechanics of materials address central questions in modern physics, such as what causes quantum phase transitions or how material properties arise from microscopic interactions. To do.
Recent research by ICFO researchers
In a recent study published in the journal nature communicationsICFO researchers Themis Sidiropoulos, Nicola Di Palo, Adam Summers, Stefano Severino, Maurizio Reduzzi, and Jens Biegert have demonstrated that by manipulating the many-body state of the material, photo-induced reported that they observed an increase and control of the electrical conductivity of graphite.
Innovative measurement technology
The researchers used carrier envelope phase-stable sub-two-cycle light pulses at 1850 nm to induce a light-matter hybrid state. They investigated the electron dynamics using attosecond soft X-ray pulses of duration 165 at the carbon K-edge of graphite at 285 eV. Attosecond soft X-ray absorption measurements probed the entire electronic structure of the material with pump-probe delay steps of attosecond intervals. The 1850 nm pump induced a highly conductive state in the material, which only exists due to light-matter interaction. Therefore, it is called a light-matter hybrid.
Researchers are interested in such conditions because they are expected to lead to quantum properties in materials that do not exist in equilibrium, and these quantum states inherently have optical speeds up to a few THz. This is because you can switch with .
However, how exactly the states manifest themselves inside the material is largely unknown. Therefore, there is much speculation in recent reports on photoinduced superconductivity and other topological phases. ICFO researchers have used attosecond pulses of soft X-rays for the first time to “look inside materials” where optical states of matter emerge.
Themis Sidiropoulos, lead author of the study, said: “The requirements for coherent exploration, attosecond time resolution, and attosecond synchronization between pump and probe are completely novel, and this This is an essential requirement for new research such as this.”
Electrodynamics of graphite
Different from twistronics or twist-by-layer grapheneWhen experimenters physically manipulate a sample and observe changes in its electronic properties, Sidiropoulos explains: “Instead of manipulating the sample, we optically excite the material with intense pulses of light, excite the electrons to a high-energy state, and observe how the electrons relax.” Within the material, only individually Observe the interactions between these charge carriers and the lattice itself, rather than as a whole system. ”
To see how electrons in graphite relax after a strong light pulse is applied, they obtained a broad X-ray spectrum and first observed how each energy state relaxes individually. and then observed how the entire electronic system is excited. Observe many-body interactions between light, carriers, and atomic nuclei at different energy levels. By observing this system, they were able to see that the energy levels of all charge carriers increase at some point in the photoconductivity of the material, indicating a trace or reminder of the superconducting phase.
Observation of coherent phonons
How could they see this? Indeed, in a previous paper, they observed coherent (non-random) phonon behavior, or collective excitation of atoms in solids. Graphite has a large number of very powerful (high-energy) phonons, which allows it to efficiently transport large amounts of energy out of the crystal without damaging the material through mechanical vibrations in the lattice. And because these coherent phonons move back and forth like waves, the electrons in the solid appear to be riding waves, creating the signature of artificial superconductivity that the researchers observed.
Impact and future prospects
The results of this study demonstrate promising applications in the field of photonic integrated circuits or optical computing, which uses light to manipulate electrons and control and manipulate material properties with light. Jens Biegert concludes: “Multi-body mechanics is at the heart of, and perhaps one of the most difficult problems in modern physics. We provide a new way to explore and manipulate the correlated phases of in real time.”
Reference: TPH Sidiropoulos, N. Di Palo, DE Rivas, A. Summers, S. Severino, M. Reduzzi, J. Biegert, “Photoconductivity enhancement and many-body effects in strongly driven photoexcited semimetallic graphite” , November 16, 2023 nature communications.
DOI: 10.1038/s41467-023-43191-5
Note
- “A sub-2-cycle, CEP-stable, 1.85-m 1-kHz pulse-driven high-flux tabletop soft X-ray source for carbon K-edge spectroscopy” by F. Silva, S. Taichmann, M. Hemmer, SL Cousin, J. Biegert, B. Bouades, September 14, 2014. optical characters.
DOI: doi:10.1364/OL.39.005383 - “Dispersive soft X-ray absorption fine structure spectroscopy of graphite with attosecond pulses” Iker León, Themistoklis PH Sidiropoulos, Irina Pi, Dooshaye Moonshiram, Antonio Picón, Jens Biegert, Nicola Di Palo, Peter Schmidt, Seth L. Cousin, Barbara Bouades and Frank Coppens, May 19, 2018. optica.
DOI: doi:10.1364/OPTICA.5.000502 - “Attosecond streaking in water windows: A new regime for attosecond pulse characterization” Seth L. Cousin, Nicola Di Palo, Bárbara Buades, Stephan M. Taichmann, M. Reduzzi, M. Devetta, A. Kheifets, G. Sansone, Written by Jens Biegert, November 2, 2017, Physical Review X.
DOI: 10.1103/PhysRevX.7.041030