Palladium hydride is a model system for studying metal-hydrogen interactions. Yet, its bulk electronic structure has proven difficult to directly probe, with most studies to date limited to surface-sensitive photoelectron spectroscopy approaches. This work reports the first in situ ambient-pressure hard X-ray photoelectron spectroscopy (AP-HAXPES) study of hydrogen incorporation in Pd thin films, providing direct access to bulk chemical and electronic information at elevated hydrogen pressures. Structural characterization by in situ X-ray diffraction and neutron reflectometry under comparable conditions establishes a direct correlation between hydrogen loading, lattice expansion, and electronic modifications. Comparison with density functional theory (DFT) reveals how hydrogen stoichiometry and site occupancy govern the density of occupied states near the Fermi level. These results resolve long-standing questions regarding PdH and establish AP-HAXPES as a powerful tool for probing the bulk electronic structure of metal hydrides under realistic conditions.

Yttrium iron garnet (YIG) is a ferrimagnetic insulator valued for its high Curie temperature, very low magnetic damping, and ability to support long-range spin-wave transport. These qualities have established it as a cornerstone material in the field of spintronics and magnonics. Most studies on YIG so far have been focused on bulk crystals, thin films, and nanoparticles, including variants with substitutions at the yttrium or iron site. New morphologies such as sub-micron flakes have drawn interest recently as their geometry and mechanical flexibility might enable different device architectures. However, detailed investigations combining their electronic structure and magnetic behavior remain scarce. In this work, we present a comparative study of the electronic and magnetic properties of a bulk-like YIG film and a sub-micron-sized YIG flake. Our results highlight the distinct behavior that emerges in sub-micron dimensions and point toward future uses for flake-based YIG in compact spintronics devices.

While electron doping in incipient ferroelectrics like SrTiO3 and KTaO3, via chemical substitution or heterostructure engineering, has revealed a wealth of collective quantum phenomena, its effect in CaTiO3 remains largely unexplored. In this work, we investigate the change in electronic properties of CaTiO3 single crystal via the introduction of oxygen vacancy. Our magnetotransport measurements reveal clear signatures of Kondo scattering, arising from the interaction between conduction electrons and localized magnetic moments. Employing hard x-ray photoemission spectroscopy combined with DFT calculations, we unravel the underlying electronic structure and demonstrate the dichotomic nature of oxygen vacancy induced electron doping: a fraction of vacancy-donated electrons occupy states near the Fermi level, driving metallic behavior, while the remainder localize in deep in-gap states, acting as magnetic moments responsible for Kondo scattering. Owing to the polar nature of ferroelastic domain walls in pristine CaTiO3 [Phys. Rev. Lett. 101, 097602 (2008)], electron-doped CaTiO3 offers a compelling platform to investigate the intricate interplay between localized magnetic moments and electric dipoles embedded within a Fermi sea. Furthermore, controlled manipulation of domain wall polarity may unlock novel functionalities, offering promising avenues for next-generation electronic devices.

Experimental tools lie at the heart of discovering science. The ability to develop transformative tools that enable unprecedented insight into the physical and chemical properties of materials will significantly advance many fields of scientific research. The visionary aim of probing and visualizing the quantum degree of freedom of materials requires a comprehensive access to orbital symmetries, spin, and dynamics of quantum states across large regions of the momentum space. Momentum microscopy stands as the most advanced experimental technique for probing the electronic structure of materials, uniquely unifying spin, orbital, time, spatial, momentum, and energy information in a single experiment. In this Perspective, we provide an overview of momentum microscopy and its applications. We review state-of-the-art all-in-one photoemission experiments and highlight recent advances enabled by momentum microscopy. We conclude this Perspective with the exciting future directions currently developing in the field.

This work presents a comprehensive investigation of the electronic structure and many-body photoemission effects in metallic platinum using reflection high-energy electron energy-loss spec- troscopy (RHEELS), soft X-ray photoelectron spectroscopy (SXPS), and hard X-ray photoelectron spectroscopy (HAXPES), supported by ab initio calculations. Shallow and deep core state spectra enable the systematic characterisation of intrinsic line-shape asymmetries and satellite structures. Correlation of photoelectron satellites with RHEELS loss features allows the assignment of inter- band transitions, surface and bulk plasmons, plasmonic overtones, and semi-core ionisation losses across the Pt spectrum. Several previously unresolved satellite features and spin-orbit splittings are identified and discussed. Comparison of experimental valence band spectra with orbital-projected densities of states calculated using ab initio density functional theory (DFT) and G0W0 approaches, with and without spin-orbit coupling, demonstrates the critical role of relativistic effects in reproducing the Pt valence electronic structure. Together, these results establish a unified, internally consistent spectroscopic reference for metallic platinum, providing a robust framework for interpreting photoelectron spectra of Pt-containing catalysts, electronic materials, and related 5d transition metal systems.

Strain-induced modifications of the electronic structure in T d - Mo 0.91 W 0.09 Te 2 were studied using hard X-ray angle-resolved photoemission spectroscopy (HARPES). Partial substitution of Mo with W stabilizes the metastable low-temperature orthorhombic T d phase of MoTe 2 . Samples were first characterized by angle-resolved photoemission spectroscopy experiments with soft X-rays and higher resolution, showing good agreement with ab initio calculations of electronic states related to topology. The modification of the bulk electronic structure due to the applied strain was assessed using operando HARPES. Applying tensile strain along the a -axis with amplitudes up to 0.34% result in changes in the bulk electronic structure as predicted by previous ab-initio calculations. In particular, the results demonstrate a strain-driven depletion of electronic states with heavy masses and high scattering rates, leading to an increase in conductivity. In contrast, tensile strain along the b -axis results in a significant increase in resistivity, which we confirmed by transport studies.

Electron correlation, hopping, and ligand-to-metal charge transfer collectively lead to diverse electronic and magnetic phenomena in 3d transition-metal oxides, where directional d orbitals make hopping highly sensitive to symmetry-dependent orbital overlap. Heterostructure engineering with atomically flat interfaces adds symmetry-breaking charge transfer as a further route to emergent behavior, yet whether interfacial mismatch between constituent oxides of a superlattice shapes ground states independent of epitaxial strain remains unresolved. Here we examine superlattices combining NdNiO_3 with Mott-insulating NdMnO_3. Varying layer thickness and combining transport with X-ray spectroscopy, we show that electron transfer from NdMnO_3 to NdNiO_3 drives a room-temperature insulating state with a distinct electronic structure, accompanied by a reversal in orbital symmetry beyond simple strain considerations, underscoring the interface's central role. These reconstructions stabilize an emergent ferromagnetic insulating state arising from interfacial Ni^2+-O-Mn^4+ superexchange. Our results establish a pathway to interface-engineered ferromagnetic insulating phases via competing interactions, with potential for spin-insulatronic applications.

MAX phases are an extremely versatile family of layered compounds that usually consist of an early to-mid transition metal (M-element), a main group element (mainly groups 13-15) or late transition metal (A-element) and carbon and/or nitrogen (X-element). It is therefore not too surprising that in addition to the roughly 70 compounds with 211 stoichiometry, there exist many solid solutions with mixed elements on the M- and A-site, respectively. Much less common are solid solution phases with mixed elements on both M- and A-site simultaneously (double-site solid solutions), as well as solid solutions on the X-site (carbonitride MAX phases). Challenging these restrictions in the chemical composition space, we present here for the first time (V0.2Cr0.8)2(Ga0.5Ge0.5)(C0.6N0.4) as a new carbonitride member of the MAX phase family, containing solid solutions on all three lattice sites simultaneously. This triple-site solid solution MAX phase is synthesized by high-temperature solid-state methods, and we demonstrate that it is possible to use two different nitrogen-containing precursors (VN and Cr2N), respectively. Structure, morphology and chemical composition are characterized by X-ray powder diffraction (XRD), electron microscopy (SEM/TEM), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (HAXPES).

The current market launch of HfO2 -based ferroelectric devices relies on the control of the inherent oxygen vacancies (OVs) and their impact on the ferroelectric performance. Due to the necessary stabilization of the ferroelectric phase by doping, several dopants are investigated for their applicability to control the vacancy concentration. Hf signatures in X-ray photoemission spectra are often used as an indication of OVs for both qualitative and quantitative analysis. The analysis of Y doped HfO2 (Y:HfO2) as investigated by hard x-ray photoelectron spectroscopy (HAXPES) reveals the inapplicability of the Hf signature for a quantitative determination of OVs in the case of heterovalent doping and is restricted to pure HfO2 or isoelectronic substitution of Hf by, for example, Zr.

The chemical versatility of MAX phases has increased almost exponentially over the last two decades, especially because of the synthesis/discovery of new solid solution phases. Many elements challenge the traditional ternary MAX phase compositions because they can be incorporated into the structure by alloying with another element, despite not forming MAX phases by themselves. Examples are (mid-to-late) transition metals that can adopt the A-site in MAX phases, some even as the sole A-element (Fe through Zn). For solid solutions, Sn has proven to be a willing A-site partner for many transition metals (Mn, Fe, Co, and Ni), even for more than one at a time. Where is the limit of transition metals that form A-site solid solutions? In this work, we demonstrate a screening of all 3d metals, except for Sc, partially substituting Sn in MAX phase Nb2SnC. We show the successful incorporation of up to 40% of V to Zn 3d metals (except for Ti), where V and Cr occupy the A-site of the MAX phase, which is demonstrated for the first time. The full series of solid solution Nb2(Sn1-xAx)C with A = V, & mldr;, Zn is studied in detail by diffraction, microscopy, and spectroscopy techniques, as well as DFT calculations, and the influence of the A-elements on the magnetic properties is discussed.

Electron glasses offer a convenient laboratory platform to study glassy dynamics, traditionally attributed to the interplay of long-range Coulomb interactions and disorder. Existing experimental studies on electron glass have focused on doped semiconductors, strongly correlated systems, granular systems, etc., which are far from the well-delocalized limit. Here, we demonstrate that the ferroelastic twin walls of well-known quantum paraelectric SrTiO3 can induce glassy electron dynamics even in a metallic phase. We show that the emergent two-dimensional electron gas at the gamma-Al2O3/SrTiO3 interface exhibits long-lasting resistance relaxations and memory effects at low temperatures, hallmarks of glassiness. Moreover, the glass-like relaxations can be tuned by the application of an electric field, implying that the observed glassy dynamics relate to the development of polarity near the structural twin walls of SrTiO3 and the complex interactions among them. The observation of this glassy metal phase also contributes to the growing understanding of the fascinating and diverse emergent phenomena near the quantum critical point.

In this work, we introduce a modified dip-and-pull electrochemical X-ray photoelectron spectroscopy (ECXPS) approach that offers new mechanistic insight into the alkaline carbon monoxide reduction reaction (CORR) over a Cu(111) single crystal surface. We tackle two major unresolved questions in the CORR mechanism that persist in the literature. Firstly, we address the mechanism for methane formation on Cu(111) and show that the mechanism likely proceeds via atomic carbon, which subsequently couples, leading to the accumulation of amorphous carbon on the surface. Secondly, we provide insight into whether the mechanism for acetate formation occurs entirely on the surface or partially within the solution phase, showing that acetate is present on the surface, indicating a surface-based reaction. These insights into surface-based mechanisms provide a handle for designing future catalysts that can efficiently target the binding of specific intermediates. Furthermore, we expect that our modified approach to dip-and-pull ECXPS - in which we have changed the electrode geometry, the method of introducing the reactant gas and used hard x-rays - will significantly expand the technique's applicability, enabling studies of the CO(2)RR and beyond.

In this work, we introduce a modified dip-and-pull ECXPS approach that offers new mechanistic insight into the alkaline CORR over a Cu(111) single crystal surface. We tackle two major unresolved questions in the CORR mechanism that persist in the literature. Firstly, we address the mechanism for methane formation on Cu(111) and show that the mechanism likely proceeds via atomic carbon, which subsequently couples, leading to the accumulation of amorphous carbon on the surface. Secondly, we provide insight into whether the mechanism for acetate formation occurs entirely on the surface or partially within the solution phase, showing that acetate is present on the surface, indicating a surface-based reaction. These insights into surface-based mechanisms provide a handle for designing future catalysts that can efficiently target the binding of specific intermediates. Furthermore, we expect that our modified approach to dip-and-pull ECXPS - in which we have changed the electrode geometry, the method of introducing the reactant gas, and used hard x-rays - will significantly expand the technique’s applicability, enabling studies of the CO(2)RR and beyond.

Hard x-ray angle-resolved photoemission spectroscopy reveals significant changes in the valence band states of EuPd2Si2 at a temperature TV , where the Eu ions undergo a temperature-induced valence crossover from a magnetic Eu2+ state to a low-temperature valence-fluctuating state. The substitution of Pd by Au and Si by Ge results in a decrease in TV and the emergence of an antiferromagnetic state at low temperatures without valence fluctuations. It has been proposed that the boundary between the antiferromagnetic order and the valence transition represents a first-order phase transition associated with a specific type of second-order critical endpoint. In this scenario, strong coupling effects between fluctuating charge, spin, and lattice degrees of freedom are to be expected. In the case of EuPd2(Si1-xGex)2 with x = 0.13, which is close to the critical endpoint, a splitting of conduction band states and the emergence of flat bands with a restriction along the P-X directions have been observed. A comparison with ab initio theory shows a high degree of agreement with the experimental results.

Abstract The surface chemistry of the Fischer-Tropsch catalytic reaction over Co has still several unknows. Here, we report an in-situ X-ray photoelectron spectroscopy study of Co $$\left(0001\right)$$ 0001 and Co( $$10\bar{1}4$$ 10 1 ¯ 4 ), and in-situ high energy surface X-ray diffraction of Co $$\left(0001\right),$$ 0001 , during the Fischer-Tropsch reaction at 0.15 bar - 1 bar and 406 K - 548 K in a H2/CO gas mixture. We find that these Co surfaces remain metallic under all conditions and that the coverage of chemisorbed species ranges from 0.4–1.7 monolayers depending on pressure and temperature. The adsorbates include CO on-top, C/-CxHy and various longer hydrocarbon molecules, indicating a rate-limiting direct CO dissociation pathway and that only hydrocarbon species participate in the chain growth. The accumulation of hydrocarbon species points to the termination step being rate-limiting also. Furthermore, we demonstrate that the intermediate surface species are highly dynamic, appearing and disappearing with time delays after rapid changes in the reactants’ composition.

Electron glasses offer a convenient laboratory platform to study glassy dynamics. Traditionally, the interplay between long-range Coulomb interactions and disorder is deemed instrumental in stabilizing the electron glass phase. Existing experimental studies on electron glass have focused on doped semiconductors, strongly correlated systems, granular systems, etc., all of which are far from the well-delocalized limit. In this work, we expand the study of electron glasses to a well-known quantum paraelectric SrTiO_3 (STO) and unveil a new scenario: how naturally occurring ferroelastic twin walls of STO could result in glassy electrons, even in a metallic state. We show that the emergent two-dimensional electron gas at the γ-Al_2O_3/STO interface exhibits long-lasting temporal relaxations in resistance and memory effects at low temperatures, which are hallmarks of glassiness. We also demonstrate that the glass-like relaxations could be further tuned by application of an electric field. This implies that the observed glassy dynamics is connected with the development of polarity near the structural twin walls of STO and the complex interactions among them, arising from the coupling between ferroelastic and ferroelectric orders. The observation of this glassy metal phase not only extends the concept of electron glasses to metallic systems with multiple order parameters but also contributes to the growing understanding of the fascinating and diverse physical phenomena that emerge near the quantum critical point.

A generic model for rolling access to synchrotron radiation experiments is presented, which has the capacity to replace call-based access models. Proposal submission, evaluation and scheduling are all executed in a rolling fashion. This significantly reduces the waiting times between proposal submission and experiment execution than that of the call-based access model. The generic rolling access model is in principle applicable to any beamlines, regardless of the number of experimental methods or setups it provides to users. This access model is flexible and could provide faster access compared to call-based access model as well as accommodate experiments and projects requiring extended preparation times.

Spin qubits are fundamental building blocks of modern quantum computing devices. The path of Ge-based hole-spin qubits has several advantages over Si-based electron-spin systems, such as the absence of valley band degeneracy, the possibility of efficient field control due to large spin-orbit coupling, and smaller effective masses. Among the possible Ge qubit devices, Ge/GeSi planar heterostructures have proven to be favourable for upscaling and fabrication. The Si concentration of the straining GeSi buffer serves as an important tuning parameter for the electronic structure of Ge/GeSi qubits. A particularly low Si concentration of x = 0.15 of the Ge$_{0.85}$Si$_{0.15}$ crystal should enable minimal lattice strain for spin qubit heterostructures, which is difficult to stabilize as a random alloy. We present a synchrotron-based study to investigate the chemical composition, valence band electronic structure and local atomic structure of a Ge$_{0.85}$Si$_{0.15}$ single crystal using the advanced combination of hard X-ray photoelectron spectroscopy (HAXPES), hard X-ray momentum microscopy (HarMoMic) and X-ray photoelectron diffraction (XPD). We found that the Ge$_{0.85}$Si$_{0.15}$ crystal has an individual, uniform valence band structure, with no signs of phase separation. The shapes of the valence bands resemble those of pure Ge, as do the low effective masses. XPD experiments and Bloch wave calculations, show the Si atoms located at Ge lattice sites within the crystal, forming a random alloy. This high chemical, electronic and structural quality of Ge$_{0.85}$Si$_{0.15}$ single-crystal substrates is of crucial importance for their implementation to enable long spin lifetimes in Ge-based hole-spin qubits. The results emphasise the power of combined X-ray spectromicroscopy techniques, which provide key insights into the qubit building blocks that form the basis of quantum technologies.

Nano-scale chemical inhomogeneity in surface oxide films formed on a V- and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron- based hard X-ray Photoelectron emission spectroscopy (HAXPES) and microscopy (HAXPEEM) as well as microscopic X-ray absorption spectroscopy (m-XAS) techniques. The results reveal the inhomogeneity in the oxide films on the micron-sized Cr2N- and VN-type particles, while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600 °C. The oxide film formed on Cr2N-type particles is rich in Cr2O3 compared with that on the martensite matrix and VN-type particles. With the increase of tempering temperature, Cr2O3 formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.

Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsV_3Sb_5 upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced non-trivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. In view of a negligible spontaneous Kerr signal in recent magneto-optical studies, the results suggest an antiferromagnetic coupling of the orbital magnetic moments along the c-axis. While the inherent structural chirality may also induce circular dichroism, the observed asymmetry values seem to be too large in the case of the weak structural distortions caused by the CDW.