Oxygen stoichiometry has been identified as a key parameter controlling superconductivity in the bilayer nickelate La3Ni2O7-delta. Using resonant inelastic x-ray scattering, we systematically investigate the evolution of orbital and spin excitations in La3Ni2O7-delta thin films with varying oxygen content. In vacuum-annealed samples, the suppression of the 1.6 eV dd excitation under pi polarization reflects appreciable inner apical-oxygen vacancies, which locally disrupt the out-of-plane p-d hybridization and the corresponding interlayer superexchange pathways. Nevertheless, the oxygen-deficient films exhibit spin excitations originating from Q = (0.25, 0.25) with a similar dispersion to the as-grown sample, suggesting a mixed ground state of double spin stripe and spin-charge stripe orders with nearly identical spin correlations. By contrast, the magnon damping rate is slightly enhanced in the vacuum-annealed sample, reflecting a modest increase in electronic disorder associated with oxygen defects. Collectively, these findings reveal that short-range spin correlations in La3Ni2O7-delta are insensitive to oxygen-vacancy-induced perturbations, including electron doping and local disruption of interlayer superexchange pathways, even in samples with appreciable oxygen deficiency, where the 1.6 eV dd excitation associated with Ni 3dz2-O 2pz hybridization is suppressed by up to 58%.

The experimental determination of the magnitude and momentum dependence of electron-phonon coupling (EPC) is an outstanding problem in condensed matter physics. The intensity of phonon peaks in Resonant Inelastic X-ray Scattering (RIXS) spectra can be related to the underlying EPC strength under significant approximations whose validity deserves careful verification. We measured the Cu L3 RIXS phonon intensity as a function of incident photon energy and momentum transfer in several layered cuprates. For CaCuO2, La2-xSrxCuO4+delta, and YBa2Cu3O6, using a generally accepted theoretical model, we quantitatively estimate the EPC for the bond-stretching mode along the high-symmetry directions (zeta,0) and (zeta,zeta), and as a function of the azimuthal angle phi at fixed q parallel to. We compare our results with theoretical predictions and find that the q parallel to-dependence of the phonon RIXS intensity can be largely ascribed to the phonon symmetry. However, a more satisfactory prediction of the experimental results requires an accurate description of the electronic structure close to the Fermi level. Our extensive investigation indicates that Cu L3 RIXS can reliably determine the momentum dependence of EPC for the bond-stretching modes of cuprates. Moreover, the large experimental basis provided here constitutes a stringent test for advanced theoretical predictions on the EPC.

Lattice vibrations carrying angular momentum, known as chiral phonons, have emerged as a promising route to control and understand complex material properties, yet their deterministic manipulation remains largely unexplored. Here we demonstrate electric-field switching of phonon angular momentum in the technologically relevant ferroelectric BaTiO3. Using circularly dichroic resonant inelastic X-ray scattering (CD-RIXS) at the oxygen K edge, we directly probe the phonon angular momentum and compare the measured dichroism with first-principles predictions of phonon-mode chirality. We find excellent agreement, revealing a momentum-dependent circular-dichroism contrast that exhibits a reversible gyroelectric effect, stable for at least 15 hours. Our results establish a robust mechanism for non-volatile control of chiral phonons and point towards new opportunities for phonon-based information and energy technologies.

Superconductivity in cuprates emerges out of a complex normal state that hosts density waves, pseudogap physics, and strange metal properties. Here, we access this normal state by synchronizing free-electron laser x-rays with high-magnetic-field pulses up to 44 T. We observe a linear increase in charge order amplitude and correlation length that persists far above the vortex melting transition. This behavior is incompatible with standard phase competition between charge order and superconductivity. By means of conventional hard x-ray diffraction and magnetostriction, we show that applied fields also enhance monoclinic lattice distortions. However, this magnetoelastic response is weaker and an epiphenomenon of the stripe order enhancement. Combined with recent observations of field-linear spin freezing, our results point to a direct coupling between magnetic field and the spin component of stripe order in the high-field normal state – a mechanism independent of superconductivity suppression that has so far remained hidden from scattering probes.

Chromium thiophosphate (CrPS4) is a long-known material: a layered semiconducting antiferromagnet. Its recently discovered gate-tunable metamagnetic phase transitions, the remarkable positive and oscillating magnetoresistance as a tunnel barrier, and its Fano-resonance luminescence, elusive among the multitude of Cr3+ compounds, call for revisiting the understanding of its electronic structure, especially regarding how it relates to magnetic order. Here, we employ X-ray magnetic circular dichroism, implemented in both absorption and resonant inelastic X-ray spectroscopies, together with quantum many-body calculations, to unveil the role of metal-ligand covalency in mediating the metamagnetic transitions in CrPS4, using crystal-field and charge-transfer excitations as fingerprints of the evolving magnetic order. We reveal the role of extended superexchange paths involving P and S atoms, coupling interactions between the Cr spins across the different magnetic phases: antiferromagnetic, canted, and ferromagnetic. Our results elucidate the electronic states involved in these phases and provide prescriptions for engineering the metamagnetic phase diagram of CrPS4.

We use resonant x-ray scattering at the nickel L_{2,3} edges to investigate the interplay between orbital degrees of freedom and charge density waves (CDWs) in the superconductor BaNi_{2}(As_{1-x}P_{x})_{2}. Both the incommensurate and commensurate CDWs in this system exhibit strong resonant enhancement with distinct energy and polarization dependencies, indicative of orbital ordering. Azimuthal-angle-dependent measurements reveal a lowering of the local Ni site symmetry, consistent with monoclinic or lower point group symmetry. The scattering signatures of both CDWs are dominated by contributions from Ni d_{xz,yz} orbitals, with similar orbital character despite their distinct wave vectors. These findings point to a shared orbital-driven formation mechanism and provide new insight into the symmetry breaking and orbital and nematic fluctuations in the high-temperature regime of the superconductor BaNi_{2}(As_{1-x}P_{x})_{2}.

We employ several X-ray based techniques, including X-ray diffraction, absorption and resonant inelastic scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn-Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of the various chemical species in shaping the physical properties of high-entropy oxides.

Ambient-pressure superconductivity in compressively strained bilayer nickelate films provides a unique platform to test pairing scenarios, yet the evolution of magnetism with carrier doping remains largely unexplored. Here, we utilize Ni L_3-edge resonant inelastic x-ray scattering to systematically track the evolution of spin and electronic excitations in coherently strained La_3-xSr_xNi_2O_7/SrLaAlO_4 thin films, spanning the superconducting (x ≤ 0.21) and overdoped non-superconducting (x = 0.38) regimes. We reveal that dispersive spin excitations, characterized by double-stripe correlations and nearly doping-independent exchange scales, persist robustly throughout the entire superconducting dome. In stark contrast, upon entering the overdoped non-superconducting state, this coherent magnetic framework undergoes an abrupt collapse, melting into a heavily damped, low-spectral-weight continuum. We show that this magnetic breakdown is fundamentally driven by a selective doping-induced orbital reconstruction. While the invariant ∼1.0 eV intra-atomic dd peak confirms an intact local octahedral crystal field, the concurrent quenching of the ∼0.4 eV and ∼1.6 eV features signifies a severe degradation of the apical-oxygen-mediated d_z^2–p_z–d_z^2 singlet sector and bilayer charge-transfer coherence. The synchronized demise of coherent spin excitations and macroscopic pairing establishes a direct, doping-controlled link, underscoring that maintaining the localized d_z^2 magnetic framework and robust apical-oxygen coupling is the fundamental prerequisite for high-T_c superconductivity in bilayer nickelates.

We use resonant X-ray scattering at the nickel L_2,3 edges to investigate the interplay between orbital degrees of freedom and charge density waves (CDW) in the superconductor BaNi_2(As_1-xP_x)_2. Both the incommensurate and commensurate CDWs in this system exhibit strong resonant enhancement with distinct energy and polarization dependencies, indicative of orbital ordering. Azimuthal-angle-dependent measurements reveal a lowering of the local Ni site symmetry, consistent with monoclinic or lower point group symmetry. The scattering signatures of both CDWs are dominated by contributions from Ni d_xz,yz orbitals, with similar orbital character despite their distinct wave vectors. These findings point to a shared orbital-driven formation mechanism and provide new insight into the symmetry breaking and orbital/nematic fluctuations in the high-temperature regime of the superconductor BaNi_2(As_1-xP_x)_2.

Magnetic MAX phase compounds are important materials for studying the two-dimensional magnetism because of their layered crystallographic structure. The hexagonal MAX phase compound Cr2GeC is a Pauli paramagnet, and here we report the induction of an ordered magnetic state by doping Fe at the Cr site. Induced magnetism for small doping concentrations (indicated as 5% and 2.5%) is found to have a weak itinerant ferromagnetic character. The Rhodes-Wohlfarth ratio is found to be 13.29, while the coefficient of electronic heat capacity (P) is 27 mJ-mol-1K-2 for Cr1.9Fe0.1GeC. Our x-ray magnetic circular dichorism measurement confirms that the magnetic moment arises from the Fe atom only, and Cr has negligible contribution towards the ordered moment. Our critical analysis indicates that the magnetic phase transition in Cr1.9Fe0.1GeC follows mean field theory.

Unraveling the mechanism behind bulk perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal films has proven challenging. This is largely due to the inherent complexity of the amorphous structure and the entangled potential origins arising from microstructure and atomic structure factors. Here, we present an approach wherein the magneto-electric effect is harnessed to induce 90° switching of bulk PMA in Tb-Co films to in-plane directions by applying voltages of only -1.2 V. This manipulation is achieved by voltage-driven insertion of hydrogen atoms into interstitial sites between Tb and Co atoms, which serves as a perturbation to the local atomic structure. Using angle-dependent X-ray magnetic circular dichroism, we find that the anisotropy switching originates from the distortion of the crystal field around Tb, which reorients the alignment of Tb orbital moments. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90°, as substantiated by ab initio calculations. Our study not only concludes the atomic origin of Tb-Co atom bonding configuration in shaping bulk PMA but also establishes the groundwork for electrically programmable ferrimagnetic spintronics, such as controlling domain wall motion and programming artificial spin textures.

The discovery of ambient-pressure superconductivity with T_c,onset > 40 K in La_3Ni_2O_7 (LNO) thin films grown on the SrLaAlO_4 (SLAO) substrate with compressive (ε≈-2%) epitaxial strain provides a unique platform for investigating the superconducting mechanism in nickelate superconductors. Here, we use resonant inelastic X-ray scattering (RIXS) to unveil the dispersive spin excitations in the LNO/SLAO thin film and establish the strain dependence of the electronic and spin excitations in LNO thin films with strain ranging from ε≈-2% to +1.9%. Compared with bulk LNO, LNO/SLAO exhibits similar dd excitations and spin dynamics, but with a larger spin-excitation bandwidth, whereas tensile-strained LNO/SrTiO_3 exhibits a marked suppression of both the spin excitations and the Ni 3d_z^2-derived dd excitations. This evolution reflects a strain-tuned interlayer exchange interaction J_z and Ni 3d_z^2-O 2p_z hybridization. Our results demonstrate how epitaxial strain modulates the interlayer magnetic coupling and are consistent with scenarios in which the interlayer antiferromagnetic superexchange interaction promotes interlayer pairing in bilayer nickelates.

We report on the electron spin resonance (ESR), heat capacity, magnetization, nuclear magnetic resonance (NMR), magnetic circular and linear dichroism (XMCD, XMLD), as well as the electrical resistivity of EuMn2P2 single crystals. Antiferromagnetic order of Eu was observed in several quantities at TNEu = 18 K. The temperature dependencies of ESR linewidth and resonance shift show, when approaching the Eu-ordered state, a divergence towards T Eu N , indicating the growing importance of magnetic correlations and the build-up of internal magnetic fields. An additional temperature scale of approximate to 47 K has considerable impact on linewidth, resonance field and intensity. This points to the presence of weak Mn-based ordering. The observed ESR line is interpreted as an Eu2+ resonance, which probes the weak magnetic background of the Mn subsystem. Such a picture is suggested by the line shape which keeps to be Lorentzian across the 47 K scale and by the ESR intensity which can be described by the same Curie-Weiss temperature above and below 47 K. In the same temperature range, anomalies were observed at 48.5 and 51 K in the heat capacity data as well as a pronounced broadening of the NMR signal of the EuMn2P2 samples. In XMCD and XMLD measurements, this weak magnetic order could not be detected in the same temperature range which might be due to the small magnetic moment, with a potential c component or frustration.

We investigate the local crystal-field environment of cerium in the clathrate compound CeBa_7Au_6Si_40 (Ce-BAS) using resonant inelastic x-ray scattering (RIXS) and magnetic susceptibility measurements. Ce-BAS is a rare example of a system where heavy-fermion physics coexists with low-energy rattling phonon modes, making it a candidate for enhanced thermoelectric performance. Magnetic susceptibility measurements reveal a temperature-dependent local moment that cannot be explained within a static crystal-field model. A fit to the susceptibility data requires strong mixing between the j = 5/2 and j = 7/2 crystal-field states, which implies large internal splittings inconsistent with RIXS spectra. In contrast, RIXS data are well described by a model with negligible j = 5/2 - j = 7/2 mixing and an energy separation of 12 meV between the ground and first excited crystal-field states. The inability to reconcile these two datasets within a static framework points to a dynamical modification of the crystal-field potential. We attribute this to coupling between the Ce 4f electrons and low-energy phonons associated with the Ce rattling motion. This interpretation is consistent with theoretical predictions of phonon-enhanced Kondo effects and dynamical Jahn-Teller distortions. Our results highlight the need for multi-orbital impurity models that include phonon coupling to fully describe the low-energy physics of Ce-BAS.

Anionic redox has reshaped the conventional way of exploring advanced cathode materials for Li-ion batteries. However, how anions participate in the redox process has been the subject of intensive debate, evolving from electron holes to O-O dimerization and currently to a focus on trapped molecular O2 based on high-resolution resonant X-ray inelastic scattering research. Here we show that the resonant X-ray inelastic scattering signal of molecular O2 is not exclusive to Li-rich oxide cathodes, but appears consistently in O-redox-inactive oxide materials even with a short beam exposure time as low as 1 min, indicating that molecular O2 species are not directly related to voltage hysteresis and voltage decay. We further demonstrated that molecular O2 is not a direct product of electrochemistry but more likely a consequence of the core excitation process in resonant X-ray inelastic scattering, for which the possible scenarios of the dissociation of 'M-(O-O)'-like species on beam excitation must be considered. Collectively, our results reconcile the conflicting reported results on the (non-)observation of molecular O2 signal collected from different beamlines and suggest that molecular O2 is not the energetic engine of new battery oxide cathodes.

LiNiO2 is a promising cathode material for Li-ion battery but its atomic and electronic structure is under debate. Indeed, two sets of Ni-O distances are identified from local structural probes that are related with either Jahn-Teller distortion or bond disproportionation of NiO6 octahedra. Moreover, LiNiO2 undergoes a monoclinic to rhombohedral transition at 200 K which origin is still unclear. On the other hand, isostructural NaNiO2 shows differences from LiNiO2, as it is a well-known Jahn-Teller distorted system, and it undergoes monoclinic to rhombohedral transition at 500 K associated to the loss of the Jahn-Teller distortion. To understand better these differences, we report here Ni L3-edge Resonant inelastic X-ray scattering experiments on LiNiO2 and NaNiO2 at different temperatures (25 to 520 K) and follow the spectral changes below and above the phase transition temperatures. The observed RIXS spectra and the mapping indicate strong spectral changes for NaNiO2 confirming the disappearance of Jahn-Teller distortion during phase transition while the changes are minor for LiNiO2 suggesting very few modifications in the local structure. Theoretical simulations of RIXS spectra are required for further understanding, however, we believe that the reported dataset can be a crucial resource for developing advanced simulations that are essential to deepening our understanding of the atomic and electronic structure of these nickelates.

We investigated the high energy spin excitations in electron-doped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$, a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at ${\mathbf{Q}}_{\ensuremath{\parallel}}=(0.6\ensuremath{\pi},0)$ and $(0.9\ensuremath{\pi},0)$ along the (1 0) direction. Our results show that, for doping level $x$ from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.

Creating high-energy-density cathodes is crucial for building next-generation lithium-ion batteries. However, materials exploration along two main directions, namely Li-rich or Ni-rich oxides, has encountered bottlenecks. To get rid of the impasse, here a "Li-rich Ni-rich" route is consolidated by designing a new family of Li1+yNi(3-5y)/3W2y/3O2 oxides with high-voltage cycling stability up to 4.5 V and high capacities over 230 mAh g-1. It is discovered that W6+ is largely incorporated into the LiNiO2 lattice, forming W/Ni(Li) inverse honeycomb-ordered nano-domains. These Li-rich domains enable reversible anionic redox, clearly demonstrated by X-ray absorption spectroscopy, resonant inelastic X-ray scattering, transmission electron microscopy, and nuclear magnetic resonance, which is linked to improved electrochemical performance. Furthermore, the incorporation of W6+ into the lattice proves to be the key to generating electrochemically active Li-rich domains irrespective of Li stoichiometry given that a similar local structure is found in W-substituted non-Li-rich oxides. This therefore implies the underestimated role of high-valence cations in tuning the structure and electrochemistry of Ni-rich oxides. These results underline the necessity of a Li-rich composition in the request for reversible high capacity, reinforcing the promise of a "Li-rich Ni-rich" avenue for developing advanced cathodes. Herein, a new family of Li-rich Ni-rich oxides Li1+yNi(3-5y)/3W2y/3O2 (y = 0, 0.03, 0.06, 0.09) with high-voltage stability up to 4.5 V and high capacities over 230 mAh g-1 is explored, which is benefited from the incorporation of W into the LiNiO2 lattice by forming a local W/Ni(Li) inverse-honeycomb superstructure that triggers reversible anionic redox at high voltage. image