Periodic Reporting for period 3 - TRANSFORMER (Structural transformations and phase transitions in real-time)
Periodo di rendicontazione: 2021-09-01 al 2023-02-28
The canonical problem addressed within the TRANSFORMER project is the real-time electron-nuclear dynamics of molecular transformation and phase transitions with two new methodologies, laser-induced electron diffraction (LIED) and attosecond soft-x-ray spectroscopy (asXANES), which we have been pioneering. The motivation for this research arises from the ubiquitous quantum many-body interaction between carriers and nuclei which is the underlying mechanism that determines the world that surrounds us. For instance, the interaction between carriers and nuclei governs the outcome of reaction pathways in chemical reactions and molecular structural change, the energy flow in organic solar cells for light harvesting, the efficiency of sensors and the efficacy of electronic information processing, the mechanisms leading to high-temperature superconductivity, or emergence of quantum phase transition. It is important to realize that while these topics constitute a wide range of exciting scientific questions, they also immediately touch aspects of modern society that need our focussed attention. For instance, presently 10% of the global energy production is used to power electronic circuits for the global internet and consumer devices, and the increasing demand is projected to increase to 20% by 2030. Similarly, chemical industry accounts for 14% of the global energy budget and is projected to increase to 19% by 2040. This, together with the prediction that these percentages will grow even faster than the total energy production, is a major source of concern, and, in addition to the pressing need to conserve energy and to reduce our environmental footprint, demands new paradigms for information processing and storage, and to design and control chemical synthesis. I like to stress that these aims translate directly into basic research to understand why and how a molecular structure changes, or how electrons and holes interact, and how the energy of the excitation dissipates into the lattice. This is especially relevant when considering that electron-phonon coupling is the origin of noise in any electronic circuit and responsible for decoherence in quantum interactions. Thus, understanding and possibly controlling the dynamics of electron photon coupling holds the key to a spectacular multitude of issues. These are all excellent examples for fundamental research with immediate implication for society and, thus, these topics are well aligned with the European Union “Missions”. The project TRANSFORMER aspires to contribute to these grand challenges by deploying powerful new research tools in investigations which target the key issue of understanding the correlated interaction between carriers and nuclei in molecular and solid-state systems.
Summarizing the work of TRANSFORMER, we are on track with both the methodical development and the envisioned experimental measurements despite prolonged shutdowns due to the pandemic situation. The ground work within O1 and O2 has been successful and is largely completed. During the investigations and campaigns, we changed some target systems, but this served to enhance our insight into the posed questions and led it to several high-profile results. These results are presently under submission or under review. We have also made excellent progress, despite the pandemic, on the core goals of following the flow of energy/excitation inside molecular and solid targets. This addresses O2 and O3.2 and a publication is presently under review.
Specifically, the investigations described within the first objective (O1) aim at establishing the limits of our two methodologies. This first step is crucial since it provides the foundation to push the boundaries of quantum dynamics into entirely new regimes of space and time dynamics of correlated quantum systems. To this end, we have conducted several successful experimental campaigns. We have shown that neutral molecules can be imaged with LIED despite ionizing the target system [Proc. Nat. Acad. Sci. 10, 1817465116 (2019)], and a publication is under submission in which we have reached the ultimate limit: We could identify and control individual quantum trajectories in LIED in joint work with Weizmann Institute. We demonstrate control over quantum dynamics to the emergence of classical trajectories. We show control over the half-cycle of the laser field from which the electron wave packet emerges. This also settles the debates on which trajectory contributes to LIED imaging, and it reduces any time uncertainty to the sub-cycle attosecond regime. We have developed an entirely new way to extract molecular structure from the LIED measurement [Nature Comm. 12, 1520 (2021)] and shown the method's efficacy on different molecular structures. Another important question (O2) that we have successfully addressed is the simultaneous electron and nuclear coordinates measurement. This touches directly on the fundamental principles of quantum physics. We could image the H2 molecule during tunnelling ionization, i.e. we could monitor the tunnel exit in momentum space, which can be related to the real space of the electrostatic potential. At the same time, we can image changes in the nuclear wave packet since ionization results in vibrational motion. The combined imaging (O2.1) allows us to view and control where the remaining second electron localizes. We can further follow the vibrational progression to the Coulomb explosion by ejection of the second electron and subsequent breakup into two protons. We are very excited by these possibilities since we unite, for the first time, attosecond imaging of electronic motion with nuclear dynamics in the same target molecule at the same time. Within O2.2 we have also successfully addressed whether we can measure electronic and nuclear structure with attosecond XANES. After a general demonstration that XANES and EXAFS can be combined to extract such information with attosecond soft-X-ray pulses [Optica 5, 502 (2018)], we have gained a much more profound understanding of the XANES measurement and the information contained in it [Appl. Phys. Rev. 8, 011408 (2021)]. This understanding has led to a new measurement in graphite [Publication under review]. We show that we can now successfully follow the entire flow of energy/excitation from the absorption of the light field inside the material and the emergence of coherence to the dephasing into electron/hole excitation, dephasing carriers coupling to phonon modes and their dispersion. We are very excited by this landmark achievement. This confirms the conjecture of the ERC proposal and allows us to apply our methodology within O3 to the dynamic evolution of phase transitions.
Specifically, the investigations described within the first objective (O1) aim at establishing the limits of our two methodologies. This first step is crucial since it provides the foundation to push the boundaries of quantum dynamics into entirely new regimes of space and time dynamics of correlated quantum systems. To this end, we have conducted several successful experimental campaigns. We have shown that neutral molecules can be imaged with LIED despite ionizing the target system [Proc. Nat. Acad. Sci. 10, 1817465116 (2019)], and a publication is under submission in which we have reached the ultimate limit: We could identify and control individual quantum trajectories in LIED in joint work with Weizmann Institute. We demonstrate control over quantum dynamics to the emergence of classical trajectories. We show control over the half-cycle of the laser field from which the electron wave packet emerges. This also settles the debates on which trajectory contributes to LIED imaging, and it reduces any time uncertainty to the sub-cycle attosecond regime. We have developed an entirely new way to extract molecular structure from the LIED measurement [Nature Comm. 12, 1520 (2021)] and shown the method's efficacy on different molecular structures. Another important question (O2) that we have successfully addressed is the simultaneous electron and nuclear coordinates measurement. This touches directly on the fundamental principles of quantum physics. We could image the H2 molecule during tunnelling ionization, i.e. we could monitor the tunnel exit in momentum space, which can be related to the real space of the electrostatic potential. At the same time, we can image changes in the nuclear wave packet since ionization results in vibrational motion. The combined imaging (O2.1) allows us to view and control where the remaining second electron localizes. We can further follow the vibrational progression to the Coulomb explosion by ejection of the second electron and subsequent breakup into two protons. We are very excited by these possibilities since we unite, for the first time, attosecond imaging of electronic motion with nuclear dynamics in the same target molecule at the same time. Within O2.2 we have also successfully addressed whether we can measure electronic and nuclear structure with attosecond XANES. After a general demonstration that XANES and EXAFS can be combined to extract such information with attosecond soft-X-ray pulses [Optica 5, 502 (2018)], we have gained a much more profound understanding of the XANES measurement and the information contained in it [Appl. Phys. Rev. 8, 011408 (2021)]. This understanding has led to a new measurement in graphite [Publication under review]. We show that we can now successfully follow the entire flow of energy/excitation from the absorption of the light field inside the material and the emergence of coherence to the dephasing into electron/hole excitation, dephasing carriers coupling to phonon modes and their dispersion. We are very excited by this landmark achievement. This confirms the conjecture of the ERC proposal and allows us to apply our methodology within O3 to the dynamic evolution of phase transitions.
TRANSFORMER has provided excellent progress beyond the state of the art in all of its aspects, i.e. in both, the establishment of new advanced experimental methods and in its scientific insight. Several publications have already appeared, are presently under review or under submission. TRANSFROMER targets the canonical problem of quantum many-body dynamics of structural phase transitions in molecular and solid-state systems through the deployment of laser-induced electron diffraction (LIED) and attosecond soft-x-ray spectroscopy (asXANES).
LIED has been implemented with a two-colour mid-IR field such that the sub-cycle delay between the two field components allowed to control the instant of tunnelling ionization, the selection of predominant quantum trajectory in the continuum and the instance of rescattering (LIED Imaging). This control has answered a heated debate over which trajectory and when the rescattering imaging exactly occurs. While this is the first work that investigates quantum control in rescattering trajectories, the same experiment has provided control over the transition between quantum to classical physics in the interference and momentum distribution of electron wave packets [publication in submission]. We have made equal progress with asXANES with molecular and solid-state systems with results published [Optica 5, 502 (2018), Appl. Phys. Rev. 8, 011408 (2021)] and publications forthcoming. We have pushed the state of the art by developing asXANES with k-shell transitions and 165 attosecond-duration soft-x-ray pulses at the carbon edge. The combined energetic coverage and attosecond time resolution has allowed us to identify electron, hole and lattice dynamics simultaneously in graphite. We could identify electron and hole dephasing mechanisms and we could identify the de-excitation pathway into the lattice [publication under review]. Overall, we have made excellent progress on several investigations which have allowed to push the boundaries of our knowledge. These results have placed us into a unique position for the reminder of the project’s duration for the investigations outlined in O3 (Real-time electronic and nuclear dynamics – isomerization and phase transition). Based on our progress, we are confident to deliver breakthrough investigations on, both, molecular and solid-state systems. For instance, we plan to conduct time-resolved experiments with LIED by adding a third pulse to initiate non-equilibrium dynamics, i.e. isomerization. For the phase transition in condensed phase (O3.2) we will apply our asXANES technique and it will be extremely exciting to investigate the dynamic evolution of a system during a phase transition. These prospects have led to new collaborations with three of the foremost theoretical groups, and to the development of string-field many-body theory [publication under preparation]. Thus, overall, we are well on track for the reminder of the TRANSFORMER project.
LIED has been implemented with a two-colour mid-IR field such that the sub-cycle delay between the two field components allowed to control the instant of tunnelling ionization, the selection of predominant quantum trajectory in the continuum and the instance of rescattering (LIED Imaging). This control has answered a heated debate over which trajectory and when the rescattering imaging exactly occurs. While this is the first work that investigates quantum control in rescattering trajectories, the same experiment has provided control over the transition between quantum to classical physics in the interference and momentum distribution of electron wave packets [publication in submission]. We have made equal progress with asXANES with molecular and solid-state systems with results published [Optica 5, 502 (2018), Appl. Phys. Rev. 8, 011408 (2021)] and publications forthcoming. We have pushed the state of the art by developing asXANES with k-shell transitions and 165 attosecond-duration soft-x-ray pulses at the carbon edge. The combined energetic coverage and attosecond time resolution has allowed us to identify electron, hole and lattice dynamics simultaneously in graphite. We could identify electron and hole dephasing mechanisms and we could identify the de-excitation pathway into the lattice [publication under review]. Overall, we have made excellent progress on several investigations which have allowed to push the boundaries of our knowledge. These results have placed us into a unique position for the reminder of the project’s duration for the investigations outlined in O3 (Real-time electronic and nuclear dynamics – isomerization and phase transition). Based on our progress, we are confident to deliver breakthrough investigations on, both, molecular and solid-state systems. For instance, we plan to conduct time-resolved experiments with LIED by adding a third pulse to initiate non-equilibrium dynamics, i.e. isomerization. For the phase transition in condensed phase (O3.2) we will apply our asXANES technique and it will be extremely exciting to investigate the dynamic evolution of a system during a phase transition. These prospects have led to new collaborations with three of the foremost theoretical groups, and to the development of string-field many-body theory [publication under preparation]. Thus, overall, we are well on track for the reminder of the TRANSFORMER project.