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-edge resonant inelastic x-ray scattering
摘要： We report an Fe L-edge resonant inelastic x-ray scattering (RIXS) study of the unusual superconductor β-FeSe. The high-energy resolution of this RIXS experiment (≈55 meV FWHM) made it possible to resolve low-energy excitations of the Fe 3d manifold. These include a broad peak which shows dispersive trends between 100 and 200 meV along the (π, 0) and (π, π) directions of the one-Fe square reciprocal lattice, and which can be attributed to paramagnon excitations. The multiband valence state of FeSe is among the most metallic in which such excitations have been discerned by soft x-ray RIXS.
关键词： RIXS,β-FeSe,Fe L-edge,dispersion,paramagnon,superconductor,resonant inelastic x-ray scattering
更新于2025-09-23 15:23:52
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Resolving the nature of electronic excitations in resonant inelastic x-ray scattering
摘要： The study of elementary bosonic excitations is essential toward a complete description of quantum electronic solids. In this context, resonant inelastic x-ray scattering (RIXS) has recently risen to becoming a versatile probe of electronic excitations in strongly correlated electron systems. The nature of the radiation-matter interaction endows RIXS with the ability to resolve the charge, spin, and orbital nature of individual excitations. However, this capability has been only marginally explored to date. Here, we demonstrate a systematic method for the extraction of the character of excitations as imprinted in the azimuthal dependence of the RIXS signal. Using this approach, we resolve the charge, spin, and orbital nature of elastic scattering, (para-)magnon/bimagnon modes, and higher-energy dd excitations in magnetically ordered and superconducting copper oxide perovskites (Nd2CuO4 and YBa2Cu3O6.75). Our method derives from a direct application of scattering theory, enabling us to deconstruct the complex scattering tensor as a function of energy loss. In particular, we use the characteristic tensorial nature of each excitation to precisely and reliably disentangle the charge and spin contributions to the low-energy RIXS spectrum. This procedure enables to separately track the evolution of spin and charge spectral distributions in cuprates with doping. Our results demonstrate a new capability that can be integrated into the RIXS toolset and that promises to be widely applicable to materials with intertwined spin, orbital, and charge excitations.
关键词： spin,resonant inelastic x-ray scattering,cuprates,azimuthal dependence,RIXS,electronic excitations,orbital,charge
更新于2025-09-23 15:22:29
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Resonant inelastic x-ray incarnation of Young’s double-slit experiment
摘要： Young’s archetypal double-slit experiment forms the basis for modern diffraction techniques: The elastic scattering of waves yields an interference pattern that captures the real-space structure. Here, we report on an inelastic incarnation of Young’s experiment and demonstrate that resonant inelastic x-ray scattering (RIXS) measures interference patterns, which reveal the symmetry and character of electronic excited states in the same way as elastic scattering does for the ground state. A prototypical example is provided by the quasi-molecular electronic structure of insulating Ba3CeIr2O9 with structural Ir dimers and strong spin-orbit coupling. The double “slits” in this resonant experiment are the highly localized core levels of the two Ir atoms within a dimer. The clear double-slit-type sinusoidal interference patterns that we observe allow us to characterize the electronic excitations, demonstrating the power of RIXS interferometry to unravel the electronic structure of solids containing, e.g., dimers, trimers, ladders, or other superstructures.
关键词： Resonant inelastic x-ray scattering,quasi-molecular orbitals,electronic excitations,Young's double-slit experiment,spin-orbit coupling,interference patterns
更新于2025-09-23 15:22:29
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Stimulated resonant inelastic x-ray scattering with chirped, broadband pulses
摘要： We present an approach for initiating and tracing ultrafast electron dynamics in core-excited atoms, molecules, and solids. The approach is based on stimulated resonant inelastic x-ray scattering induced by a single, chirped, broadband XUV or x-ray pulse. A first interaction with this pulse prepares a core-excited state wave packet by resonant core-excitation. A second interaction with the pulse at a later time induces the transition to valence-excited states, which is associated with stimulated emission. The preparation of the core-excited wave packet and the transition from the core-excited states to the valence-excited states occur at distinct chirp-dependent times. As a consequence, the stimulated emission carries information about the time evolution of the core-excited state wave packet.
关键词： XUV pulses,x-ray pulses,core-excited states,ultrafast electron dynamics,chirped pulses,stimulated resonant inelastic x-ray scattering
更新于2025-09-19 17:15:36
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Decoupling Carrier Concentration and Electron-Phonon Coupling in Oxide Heterostructures Observed with Resonant Inelastic X-Ray Scattering
摘要： We report the observation of multiple phonon satellite features in ultrathin superlattices of the form nSrIrO3=mSrTiO3 using resonant inelastic x-ray scattering (RIXS). As the values of n and m vary, the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the RIXS cross section, we extract the variation in the electron-phonon coupling strength as a function of n and m. Combined with the negligible carrier doping into the SrTiO3 layers, these results indicate that the tuning of the electron-phonon coupling can be effectively decoupled from doping. This work both showcases a feasible method to extract the electron-phonon coupling in superlattices and unveils a potential route for tuning this coupling, which is often associated with superconductivity in SrTiO3-based systems.
关键词： superlattices,electron-phonon coupling,SrTiO3,SrIrO3,resonant inelastic x-ray scattering
更新于2025-09-09 09:28:46
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Stochastic stimulated electronic x-ray Raman spectroscopy
摘要： Resonant inelastic x-ray scattering (RIXS) is a well-established tool for studying electronic, nuclear, and collective dynamics of excited atoms, molecules, and solids. An extension of this powerful method to a time-resolved probe technique at x-ray free electron lasers (XFELs) to ultimately unravel ultrafast chemical and structural changes on a femtosecond time scale is often challenging, due to the small signal rate in conventional implementations at XFELs that rely on the usage of a monochromator setup to select a small frequency band of the broadband, spectrally incoherent XFEL radiation. Here, we suggest an alternative approach, based on stochastic spectroscopy, which uses the full bandwidth of the incoming XFEL pulses. Our proposed method is relying on stimulated resonant inelastic x-ray scattering, where in addition to a pump pulse that resonantly excites the system a probe pulse on a specific electronic inelastic transition is provided, which serves as a seed in the stimulated scattering process. The limited spectral coherence of the XFEL radiation defines the energy resolution in this process and stimulated RIXS spectra of high resolution can be obtained by covariance analysis of the transmitted spectra. We present a detailed feasibility study and predict signal strengths for realistic XFEL parameters for the CO molecule resonantly pumped at the O1s ! p(cid:2) transition. Our theoretical model describes the evolution of the spectral and temporal characteristics of the transmitted x-ray radiation, by solving the equation of motion for the electronic and vibrational degrees of freedom of the system self consistently with the propagation by Maxwell equations.
关键词： CO molecule,covariance analysis,Stochastic stimulated electronic x-ray Raman spectroscopy,resonant inelastic x-ray scattering,XFEL
更新于2025-09-04 15:30:14
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Demonstration of resonant inelastic x-ray scattering as a probe of exciton-phonon coupling
摘要： Resonant inelastic x-ray scattering (RIXS) is a promising technique for obtaining electron-phonon coupling constants. However, the ability to extract these coupling constants throughout the Brillouin zone for crystalline materials remains limited. To address this need, we developed a Green’s function formalism to capture electron-phonon contributions to core-level spectroscopies without explicitly solving the full vibronic problem. Our approach is based on the cumulant expansion of the Green’s function combined with many-body theory calculated vibrational coupling constants. The methodology is applied to x-ray photoemission spectroscopy, x-ray absorption spectroscopy (XAS), and RIXS. In the case of the XAS and RIXS, we use a two-particle exciton Green’s function, which accounts implicitly for particle-hole interference effects that have previously proved difficult. To demonstrate the methodology and gain a deeper understanding of the experimental technique, we apply our formalism to small molecules, for which unambiguous experimental data exist. This comparison reveals that the vibronic coupling constant probed by RIXS is in fact related to exciton-phonon coupling rather than electron-phonon coupling, challenging the conventional interpretation of the experiment.
关键词： electron-phonon coupling,Green’s function formalism,exciton-phonon coupling,Resonant inelastic x-ray scattering,vibronic coupling
更新于2025-09-04 15:30:14