Two-dimensional electron dynamics reconstructed by polarization-resolved high harmonic spectroscopy

We introduce a neuromorphic reservoir computing concept that leverages the complex interplay between electronic and ionic states in lead halide perovskites to run algorithms by harnessing opto-ionic modulation of photoexcited state populations. The system leverages the heterogeneous material microstructure and ultrafast spatio-temporal electronic state dynamics in perovskite microcrystals to generate a high-dimensional internal state space reservoir within the charge carrier populations. This reservoir exhibits complex, nonlinear, and adaptive behavior. The computation output is read directly from the photogenerated luminescence using diffraction-limited resolution with 106 nodes per cm2 and energy of 800 pJ per node-operation. The system performs robustly in distinguishing 4-bit pulse sequences with a mean accuracy of 87%, showcasing its potential for neuromorphic computing tasks. Our work reveals excited-state dynamics as a platform for exploring nanoscale computing with photoactive materials, also at high speeds using ultrafast photophysics, with large potential for the development of next-generation neuromorphic technologies.

Synergistic electronic structure and lattice dynamics mechanisms for hydrogen diffusion in nickel oxide

ESIPT process of a chalcone derivative: Electronic structure calculations and nonadiabatic dynamics simulations

The microscopic mechanisms of electronic energy loss and charge redistribution induced by slow ions in wide-bandgap semiconductors are central to ion implantation and radiation-tolerant device design. Using real-time time-dependent density functional theory, we investigate the electronic stopping power and transient charge dynamics of neutral H, B and N projectiles channeled along the <001> direction in 4H-SiC over velocities of 0.1-0.6 a.u. The energy deposition profiles display pronounced oscillations that follow the periodic modulation of the crystal's electron density, while the overall stopping scales linearly with velocity and increases systematically with projectile atomic number. The calculated stopping powers are in good quantitative agreement with stopping and range of ions in matter data in the pre-Bragg-peak regime. The longitudinal force on the projectiles and nearby host atoms shows pronounced oscillations, with amplitudes mainly determined by the projectile species. Hirshfeld charge analysis shows that the carbon atom experiences transient electron depletion, the silicon atom tends to accumulate electrons, and the projectiles develop strongly species- and velocity-dependent effective charges, most pronounced for N. Real-space charge-density-difference maps further demonstrate that the induced nonequilibrium response is highly localized around C-2p orbitals and tracks the ion on sub-femtosecond time scales. These results provide a coherent microscopic picture of ultrafast, nonadiabatic electronic stopping processes in 4H-SiC under low-velocity ion irradiation.

The photochemical CO2 reduction reaction (CRR) represents a zero-carbon pathway for converting CO2 into value-added chemicals, yet its industrial implementation has been constrained by low selectivity and product diversity. Dirac nodal arc semimetals characterized by ultrahigh carrier mobility (>25000 cm2·V-1·s-1) offer a promising platform to search for efficient catalysts for CO2 conversion. Herein, we demonstrate that strategic Pt incorporation into PdSn4 optimizes the electronic structure and carrier dynamics of this Dirac semimetal. Experimental and theoretical analyses reveal that the resulting Pd─Sn─Pt local electronic structure redistributes charge density around Pd and Pt atoms, which facilitates C─C coupling via *OC─COH and *OC─CHOH intermediates and enhances carrier mobility by 40% versus the pristine PdSn4 single crystal. The optimized Pd0.4Pt0.6Sn4 single crystal achieves C2H4 i) formation rate of 328 µmol∙g-1∙h-1; ii) product selectivity of 73.1%; iii) electron-based selectivity of 89%. This work establishes electronic-structure-tunable Dirac semimetals as a new paradigm for multi-carbon photochemical CO2 reduction, providing a design strategy for next-generation photocatalysts.

We present a graph-based machine-learning framework for simulating the time evolution of electronic wavefunctions and densities in quantum systems. Inspired by parallels between time-dependent quantum propagators and spectral graph convolutions, we employ a recursive Chebyshev graph neural network architecture capable of learning the dynamics of electronic processes across a range of external potentials and Hamiltonians. Two model variants are introduced: one that evolves the full complex-valued wavefunction and the other that propagates only the electron density. Both models are trained on trajectory data generated from tight-binding Hamiltonians and a time-dependent electron-phonon coupled system. Our results demonstrate that wavefunction-based models achieve near-exact long-time propagation across static and dynamic regimes, while density-only models maintain strong performance using physics-informed loss functions, even in the absence of phase information. This work lays the foundation for coarse-grained, resolution-independent propagators for electronic dynamics and opens new pathways for scalable quantum simulations in complex molecular and condensed-phase systems.

Abstract Plasmonic nanostructures photoexcited with ultrashort light pulses exhibit a strong nonlinear optical response driven by nonequilibrium ‘hot’ carriers. Studying the spectro‐temporal evolution of such nonlinearities to extract information on hot electron dynamics has attracted significant interest, given the unparalleled opportunities unlocked by these high‐energy carriers in fields ranging from photocatalysis to optical communications. However, in typical samples of size‐dispersed nanoparticles, effects such as inhomogeneous broadening and pump‐pulse‐induced selectivity can distort the system response, hindering accurate characterizations. This study dissects the ultrafast response of polydisperse gold nanorods employing two‐dimensional electronic spectroscopy (2DES), a powerful technique offering a unique combination of temporal and spectral resolution. The ultrabroadband pulses cover both the transverse and longitudinal nanorod resonances, enabling an accurate analysis of their distinct behavior. By complementing experiments with a quantitative model of hot‐carrier‐mediated nonlinearities that incorporates sample polydispersity, the broadband excitation, and the nanorods’ resonant absorption, the work provides a comprehensive understanding of the underlying mechanisms and identifies fingerprints of electron–electron scattering in the 2DES maps. Performed on a simple yet prototypical system, this analysis advances the study of plasmonic hot carriers and supports further applications of 2DES to explore ultrafast mechanisms in more advanced hybrid plasmon‐based systems, e.g. strongly‐coupled complexes.

Abstract Strong electron–neutral collisions in atmospheric-pressure plasma jets constrain the electron energy distribution, which governs plasma chemistry. Here, we demonstrate phase-resolved EEDF measurements in a dual-frequency atmospheric-pressure plasma jet (DF-APPJ) using laser Thomson scattering spectroscopy combined with Bayesian inference. The plasma jet sustained by a continuous 5 MHz sinusoidal power is modulated using a counter electrode, onto which the plasma impinges, with a 50 kHz bipolar square-wave bias. Nanosecond-resolved, incoherent TS spectra were analysed to determine not only electron density and temperature but also the electron energy distribution function, which quantifies deviations from Maxwellian energy distributions. We observe phase dependent transitions in the EEDF, shifting toward a Maxwellian-like shape during negative voltage transitions and exhibiting weakly Druyvesteyn-like features during positive transitions of the applied low-frequency waveform. This study establishes a quantitative framework for time-resolved electron kinetics in dual-frequency APPJs and highlights the potential of Bayesian-enhanced TS for kinetic analysis in highly collisional plasmas.

Dynamics of surface electrons in a topological insulator: Cyclotron resonance at room temperature

Breast cancer remains a significant global health burden, with a rising incidence and mortality rate, particularly among younger women. Despite substantial therapeutic progress, effective molecular targets for treatment remain limited. This study investigated the oncogenic function of telomerase reverse transcriptase (TERT) and assessed the anti-cancer potential of formononetin using integrated bioinformatics and computational analyses. Pharmacokinetic and toxicity profiles were assessed using SwissADME, pkCSM, and Protox-II. Potential drug and disease targets were retrieved from SwissTarget, TargetNet, GeneCards, and DisGeNET databases, identifying 45 overlapping targets. Protein-protein interaction mapping via STRING and topological analysis in Cytoscape highlighted TERT, PIK3CA, ESR1, and KIT as key nodes. Molecular docking revealed high binding affinities of formononetin toward TERT (- 8.15kcal/mol) and PIK3CA (- 8.01kcal/mol). Gene expression profiling using GEPIA2 confirmed significant over expression of TERT and PIK3CA in breast carcinoma tissues. Pathway enrichment analysis, conducted through ShinyGO, in conjunction with density functional theory (DFT) calculations, elucidated the electronic and interaction dynamics underlying ligand-target stability. Collectively, these findings suggest that formononetin may be a promising lead compound for targeting TERT-driven breast cancer, warranting further in vivo and clinical validation to establish its therapeutic potential.

Most advances in electronic spin-dependent non-adiabatic dynamics focus on refining the underlying dynamics methods. In contrast, this work considers an improved description of spin-orbit coupling by explicitly accounting for its relativistic origins. To this end, we extend a standard one-electron triatomic Jahn-Teller model to the four-component relativistic domain. In our formulation, the electron is treated using the Dirac-Coulomb Hamiltonian, while the nuclei remain non-relativistic, departing from the conventional formulation that incorporates the Pauli spin-orbit coupling as a perturbation. The most striking difference between our relativistic model and the conventional one is the presence of vibronic coupling terms on the anti-diagonal of the diabatic potential matrix. These terms scale as 1/c2 and, although nominally small, they can be amplified near avoided-crossings or in systems with heavy nuclei. Furthermore, their presence implies that nuclear motion can affect the direction of the electron spin, a feature entirely absent in the non-relativistic formulation of our model. In the adiabatic representation, the couplings translate to non-Abelian characteristics of the non-adiabatic coupling matrix that persist even in the Born-Oppenheimer approximation. Within our model setting, a relativistic formulation allows for a more intricate interplay between the electronic spin and nuclear degrees of freedom.

The rod-like Au42(SC8H9)32 monolayer-protected cluster (MPC) was studied using two-dimensional electronic spectroscopy (2DES). This study combined analysis of the excitation power, cross-peak specific maps, and time-dependent 2DES signals that resulted from excitation of a longitudinal electronic resonance at 13 500 cm-1. The Au42(SC8H9)32 longitudinal resonance is of interest due to the exceptional photothermal efficiency of this MPC. A traditional plasmonic gold nanorod is used throughout as a point of comparison. The excitation power study and 2DES results obtained from excitation of the longitudinal resonance were distinct from plasmonic excitations, thus implicating it as an exitonic system. The time-dependent signal amplitudes of 2DES cross-peaks showed that the longitudinal mode consisted of multiple electronic fine structure states that internally converted in a state-to-state manner. Taken together, these results point to a manifold of nondegenerate electronic states, rather than a collective plasmon resonance, that comprise the longitudinal mode excitation and dynamics of Au42(SC8H9)32.

Photothermal efficiency in MXenes arises from the complex interplay between electronic structure and lattice dynamics, yet the precise contribution of electron-phonon coupling (EPC) remains poorly understood. By integrating ab initio nonadiabatic carrier-dynamics simulations with state-resolved electron-phonon-coupling analysis, the intrinsic mechanisms governing photothermal conversion in MXene materials are elucidated. Results reveal that MXene photothermal performance is dictated by an intrinsic hierarchy of EPC channels and hot-phonon accumulation, whereas defect-mediated non-radiative recombination serves as a secondary channel and ultimately compromises long-term photothermal stability. Building on this mechanistic insight, a physics-inspired and AI-assisted molecular-screening framework is developed to identify surface passivation chemistries capable of extending hot carrier lifetimes and mitigating phonon bottlenecks. Guided by this paradigm, a composite film endowed with a concave-spherical light-trapping array was fabricated, leading to substantial improvements in photothermal conversion efficiency and operational stability. This quantum-to-device co-design paradigm transcends MXenes, providing a data-driven, systematic design pathway that integrates fundamental theory with surface passivation to accelerate the advancement of durable photothermal devices tailored for sustainable energy applications.

Abstract To investigate high-speed airflow’s impact on discharge brushes’ corona discharge characteristics and charge dissipation efficiency, a COMSOL Multiphysics numerical model was built. It analyzed distributions and dynamics of electrons, positive/negative ions at the brush tip under quiescent air and 100 m/s airflow. Results show that no airflow causes ion accumulation (low mobility) and electric field shielding, suppressing discharge and reducing efficiency; high-speed airflow accelerates ion transport, weakens shielding, enhances discharge intensity/stability and positive ion migration, improving efficiency. This confirms airflow’s key role, with future designs needing aerodynamic considerations.

Manipulating intensity, phase and polarisation of the electromagnetic fields on ultrafast timescales is essential for all-optical switching, optical information processing and development of novel time-variant media. Noble metal based plasmonics has provided numerous platforms for optical switching and control, enabled by strong local field enhancement, artificially engineered dispersion and strong Kerr-type free-electron nonlinearities. However, achieving precise control over switching times and spectral response remains challenging, often limited by hot-electron gas relaxation on picosecond timescales and by the intrinsic band structure of the materials. Here, we experimentally demonstrate a strong and tunable nonlinearity in a metamaterial-on-a-mirror geometry, controlled by the wavelength of excitation, which imprints a specific, non-uniform hot-electron population distribution, driving targeted electron and lattice dynamics. The synergistic exchange of electromagnetic, electronic and mechanical energies enables reflection changes on sub-300 fs timescales in selected spectral ranges, surpassing the limitations imposed by the inherent material response of metamaterial constituents. The observed effect–present in reflection due to leaky guided modes of the metamaterial, but absent in transmission–is highly spectrally selective and sensitive to polarisation of light, opening a pathway to tailoring switching rates through the choice of operating wavelength and nanostructure design. The ability to manipulate temporal, spectral, and mechanical aspects of light-matter interactions underscores new opportunities for nonlinear optical applications where polarisation diversity, spectral selectivity, and ultrafast modulation are important.

The control of out-of-equilibrium electron dynamics in topological insulators is essential to unlock their potential in next-generation quantum technologies. However, the role of temperature on the renormalization of the electronic band structure and, consequently, on out-of-equilibrium electron scattering processes is still elusive. Here, using high-resolution time- and angle-resolved photoemission spectroscopy (TR-ARPES), we show that even a modest (~15 meV) renormalization of the conduction band of Bi2Te3 can critically affect bulk and surface electron scattering processes. Supported by kinetic Monte Carlo simulations, we show that temperature-induced changes in the bulk band structure modulate the intervalley electron-phonon scattering rate, reshaping the out-of-equilibrium response and the long-lasting charge accumulation at the bottom of the conduction band. This work establishes temperature as an effective control knob for engineering scattering pathways in topological insulators.

Coherent nonlinear light-matter interaction with X-rays gives access to a regime in ultrafast spectroscopy in which atomic resolution meets femtosecond and attosecond timescales1,2. Particularly, X-ray four-wave mixing, involving several resonant transitions in a single coherent nonlinear process, has the potential to provide information on the electronic states coupling, coherent electron motion, correlation and dynamics, with state and site selectivity3-5. Here we demonstrate coherent, background-free four-photon interactions with core-shell electrons using single broadband X-ray pulses from a free-electron laser. The all-X-ray four-wave mixing signals, measured in gaseous neon, arise from doubly resonant nonlinear processes involving Raman transitions6, including X-ray coherent anti-Stokes electronic Raman scattering. The 2D spectral maps (photon-in/photon-out) represent a step towards multidimensional correlation spectroscopy at the atomic scale. Using a multicolour time-delayed X-ray pulse scheme, we further demonstrate the feasibility of extending the proposed methodology to the ultrafast time domain. These results reveal potential for studying localized electron dynamics in multiple systems, from biomolecules to correlated quantum materials, with applications in areas such as energy conversion, biomedical imaging and quantum information technologies.

The ultrafast electronic relaxation dynamics of tetrakis(dimethylamino)ethylene (TDMAE) following photoexcitation at ∼267 nm is investigated using the time-, angle- and kinetic-energy-resolved photoelectron spectroscopy method, since we are motivated by the experimental findings in a previous similar study (E. Gloaguen et al., J. Am. Chem. Soc., 2005, 127, 16529-16534). Based on the detailed analysis of the current high-quality data, the lifetime of the initially prepared ππ* state is found to be 50 ± 10 fs and it is clearly evident that an intermediate Rydberg state with a lifetime of 550 ± 50 fs plays a pivotal role in the photodynamics of TDMAE. In addition, a partial wave packet revival is also observed with a period of ∼500 fs. This coherent oscillation, which is attributed to a vibrational quantum beat associated with overtones of the low-frequency C-C twist vibration in TDMAE, survives the ultrafast internal conversion processes and finally damps on a time scale of the order of several picoseconds.

Photoionization time delay in atoms and molecules is a fundamental phenomenon in attosecond physics, encoding essential information about electronic structure and dynamics. Compared with atoms, molecules exhibit anisotropic potentials and additional nuclear degrees of freedom, which make the interpretation of molecular photoionization time delays more intricate but also more informative. In this work, we investigate the dependence of the photoionization time delay on the internuclear distance in the &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ 5\sigma \to k\sigma$\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt; ionization channel of carbon monoxide (CO) molecules. The molecular ground state is obtained using the Hartree-Fock method, and the photoionization process is treated within quantum scattering theory based on the iterative Schwinger variational principle of the Lippmann–Schwinger equation. Numerical calculations are performed with the ePolyScat program to obtain molecular-frame differential photoionization cross sections and time delays at various internuclear distances. Our results show that the extrema of the photoionization time delay occur near the peaks and dips of the differential cross section and shift toward lower energies as the internuclear distance &lt;i&gt;R&lt;/i&gt; increases. At low energies, the time delay along the oxygen end increases with &lt;i&gt;R&lt;/i&gt;, while that along the carbon end decreases, which is attributed to the asymmetric charge distribution and the resulting short-range potential difference between the two atomic sites. Around the shape-resonance energy region, both cross section and time delay display pronounced peaks associated with an &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ l=3$\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt; quasi-bound state. As &lt;i&gt;R&lt;/i&gt; increases, the effective potential barrier broadens, the quasi-bound state energy moves to lower values, and its lifetime becomes longer, leading to enhanced resonance amplitude and increased time delay. In the high-energy region, opposite-sign peaks of time delay are found along the O and C directions, corresponding to minima in the cross section. These features are well explained by a two-center interference model, where increasing &lt;i&gt;R&lt;/i&gt; shifts the interference minima and the associated time-delay peaks toward lower energies. This study provides deeper insights into the photoionization dynamics of CO molecules, accounting for the role of nuclear motion, and offers valuable references for studying the photoelectron dynamics of more complex molecular systems.