Extending resonant inelastic X-ray scattering to the extreme ultraviolet

Abstract

In resonant inelastic X-ray scattering (RIXS), core hole resonance modes are used to enhance coupling between photons and low energy electronic degrees of freedom. Resonating with shallow core holes accessed in the extreme ultraviolet (EUV) can provide greatly improved energy resolution at standard resolving power, but has been found to often yield qualitatively different spectra than similar measurements performed with higher energy X-rays. This paper uses experimental data and multiplet-based numerical simulations for the M-edges of Co-, Ni-, and Cu-based Mott insulators to review the properties that distinguish EUV RIXS from more commonly performed higher energy measurements. Key factors such as the origin of the strong EUV elastic line and advantages of EUV spectral functions over soft X-ray RIXS for identifying intrinsic excitation line shapes are discussed.

Extreme ultraviolet resonant inelastic X-ray scattering (RIXS) at a seeded free-electron laser

“…RXES is very strong in the EUV regimes and it yields intense and unavoidable off-specular reflectivity that produces an elastic line in the RIXS spectra normally several orders of magnitude stronger than the inelastic features. Such strong elastic line often obscures the signal in the few hundred meV energy loss range12.…”

“…Several soft X-ray RIXS instruments (or beamlines) under development at the LCLS (Stanford, USA) and European XFEL (Hamburg, Germany) will soon be operational. However, it has been shown recently that the extension of RIXS into the EUV energy range (10 eV < hν < 120 eV) is of great advantage for studying certain classes of materials121314. At these photon energies, high energy resolution can be achieved even with commercial spectrometers.…”

Charge transfer excitations in VUV and soft X-ray resonant scattering spectroscopies

“…The basic parameters of the AM calculation are similar to those used in Ref. [4,8,9]. The crystal field is described by the parameter 10Dq=0.56 eV, and the Slater-Condon parameters that govern 2-particle angular momentum coupling are set to atomic values (80% of bare Hartree-Fock values).…”

“…For example, the M-edge VUV resonant inelastic X-ray scattering (RIXS) spectrum of NiO in Fig. 1(a, right), shows a far weaker charge transfer peak than L-edge soft X-ray RIXS [4][5][6][7][8], and M-edge XAS from NiO has no obvious charge transfer derived spectral feature. Here, we will explore the question of how charge transfer states manifest in the VUV by varying the core hole modeling parameters of an atomic multiplet (AM) simulation for NiO, augmented by ligand hybridization treated in the single Anderson impurity model (SAIM).…”

Second derivative analysis and alternative data filters for multi-dimensional spectroscopies: A Fourier-space perspective

“…The past few decades have seen rapid improvement of throughput, resolution, and other fundamental capabilities for momentum-resolving spectroscopies such as angle resolved photoemission (ARPES) and resonant inelastic X-ray scattering (RIXS) [1][2][3][4][5]. The features observed with these techniques disperse in a multi-dimensional space with axes of momentum and energy, and can reveal the kinetics of quasiparticles that define the low energy properties of many-body systems.…”