Knowing the pressure dependence of glass forming liquids is important in various contexts. Here, we study the case of supercooled water, which has at least two different amorphous states with different densities. The pressure dependencies of the two glass transitions are predicted to show opposite behaviour, crossing in the P-T plane at elevated pressure. The experimental identification of the glass transition at elevated pressure and cryo-conditions is technically difficult. Moreover, in the case of amorphous ices, the glass transition is interrupted by crystallization, which makes it even more challenging. We show the feasibility of performing X-ray photon correlation spectroscopy experiments at elevated pressure using a diamond anvil cell at cryogenic temperatures. We observe two dynamic components when approaching the glass transition temperature. For high-density amorphous ice at a pressure of around (0.08 ± 0.02) GPa we determine the glass transition to be at higher temperatures compared to ambient conditions.

Recent experiments and theoretical studies strongly indicate that water exhibits a liquid-liquid phase transition (LLPT) in the supercooled domain. An open question is how the LLPT of water can affect the properties of aqueous solutions. Here, we study the structural and thermodynamic properties of supercooled glycerol-water microdroplets at dilute conditions (χg = 3.2% glycerol mole fraction). The combination of rapid evaporative cooling with femtosecond X-ray scattering allows us to outrun crystallization and gain access to the deeply supercooled regime down to T = 229.3 K. We find that the density fluctuations of the glycerol-water solution or, equivalently, its isothermal compressibility, κT, increases upon cooling. This is confirmed by molecular dynamics simulations, which indicate that the presence of glycerol shifts the temperature of maximum κT from T = 230 K in pure water down to T = 223 K in the solution. Our findings elucidate the interplay between the complex behavior of water, including its LLPT, and the properties of aqueous solutions at low temperatures, which can have practical consequences in cryogenic biological applications and cryopreservation techniques.

Modification of graphene electronic properties via contact with atoms of different kind allows for designing a number of functional post-silicon electronic devices. Specifically, 2D metallic layer formation over graphene is a promising approach to improving the electronic properties of graphene-based systems. In this work we analyse the electronic and spin structure of graphene synthesized on Pt(111) after sodium monolayer adsorption by means of angle-resolved photoemission spectroscopy and ab initio calculations. Here, we show that sodium layer formation leads to a shift of the graphene pi states towards higher binding energies, but the most intriguing property of the studied system is the appearance of a partially spin-polarized Kanji symbol-like feature resembling the graphene Dirac cone in the electronic structure of adsorbed sodium. Our findings reveal that this structure is caused by a strong interaction between Na orbitals and Pt 5d spin-polarized states, where the graphene monolayer between them serves as a mediator of such interaction.

Hydrated proteins undergo a transition in the deeplysupercooledregime, which is attributed to rapid changes in hydration water andprotein structural dynamics. Here, we investigate the nanoscale stress-relaxationin hydrated lysozyme proteins stimulated and probed by X-ray PhotonCorrelation Spectroscopy (XPCS). This approach allows us to accessthe nanoscale dynamics in the deeply supercooled regime (T = 180 K), which is typically not accessible through equilibriummethods. The observed stimulated dynamic response is attributed tocollective stress-relaxation as the system transitions froma jammed granular state to an elastically driven regime. The relaxationtime constants exhibit Arrhenius temperature dependence upon coolingwith a minimum in the Kohlrausch-Williams-Watts exponentat T = 227 K. The observed minimum is attributedto an increase in dynamical heterogeneity, which coincides with enhancedfluctuations observed in the two-time correlation functions and amaximum in the dynamic susceptibility quantified by the normalizedvariance chi( T ). The amplification offluctuations is consistent with previous studies of hydrated proteins,which indicate the key role of density and enthalpy fluctuations inhydration water. Our study provides new insights into X-ray stimulatedstress-relaxation and the underlying mechanisms behind spatiotemporalfluctuations in biological granular materials.

Hard x-ray angle-resolved photoemission spectroscopy reveals the momentum-resolved band structure in an epitaxial Mn₂Au(001) film capped by a 2-nm-thick ferromagnetic permalloy layer. By magnetizing the permalloy capping layer, the exceptionally strong exchange bias aligns the Néel vector in the Mn₂Au(001) film accordingly. Uncompensated interface Mn magnetic moments in Mn₂Au were identified as the origin of the exchange bias using x-ray magnetic circular dichroism in combination with photoelectron emission microscopy. Using time-of-flight momentum microscopy, we measure the asymmetry of the band structure, E(k)≠E(-k), in Mn₂Au resulting from the homogeneous orientation of the Néel vector. Comparison with theory shows that the Néel vector, determined by the magnetic moment of the top Mn layer, is antiparallel to the permalloy magnetization. The experimental results demonstrate that hard x-ray photoemission spectroscopy can measure the band structure of epitaxial layers beneath a metallic capping layer and corroborate the asymmetric band structure in Mn₂Au that was previously inferred only indirectly.

The understanding of antiferromagnetic domain walls, which are the interface between domains with different Néel order orientations, is a crucial aspect to enable the use of antiferromagnetic materials as active elements in future spintronic devices. In this work, we demonstrate that in antiferromagnetic NiO/Pt bilayers arbitrary-shaped structures can be generated by switching driven by electrical current pulses. The generated domains are T domains, separated from each other by a domain wall whose spins are pointing toward the average direction of the two T domains rather than the common axis of the two planes. Interestingly, this direction is the same for the whole domain wall indicating the absence of strong Lifshitz invariants. The domain wall can be micromagnetically modeled by strain distributions in the NiO thin film induced by the MgO substrate, deviating from the bulk anisotropy. From our measurements we determine the domain-wall width to have a full width at half maximum of Δ=98±10 nm, demonstrating strong confinement.

Studying protein interactions at low temperatures hasimportantimplications for optimizing cryostorage processes of biological tissue,food, and protein-based drugs. One of the major issues is relatedto the formation of ice nanocrystals, which can occur even in thepresence of cryoprotectants and can lead to protein denaturation.The presence of ice nanocrystals in protein solutions poses severalchallenges since, contrary to microscopic ice crystals, they can bedifficult to resolve and can complicate the interpretation of experimentaldata. Here, using a combination of small- and wide-angle X-ray scattering(SAXS and WAXS), we investigate the structural evolution of concentratedlysozyme solutions in a cryoprotected glycerol-water mixturefrom room temperature (T = 300 K) down to cryogenictemperatures (T = 195 K). Upon cooling, we observea transition near the melting temperature of the solution (T & AP; 245 K), which manifests both in the temperaturedependence of the scattering intensity peak position reflecting protein-proteinlength scales (SAXS) and the interatomic distances within the solvent(WAXS). Upon thermal cycling, a hysteresis is observed in the scatteringintensity, which is attributed to the formation of nanocrystallitesin the order of 10 nm. The experimental data are well described bythe two-Yukawa model, which indicates temperature-dependent changesin the short-range attraction of the protein-protein interactionpotential. Our results demonstrate that the nanocrystal growth yieldseffectively stronger protein-protein attraction and influencesthe protein pair distribution function beyond the first coordinationshell.

Here, we demonstrate an experimental proof of concept for nanofocused x-ray photon correlation spectroscopy, a technique sensitive to nanoscale fluctuations present in a broad range of systems. The experiment, performed at the NanoMAX beamline at MAX IV, uses a novel event-based x-ray detector to capture nanoparticle structural dynamics with microsecond resolution. By varying the nanobeam size from σ=88 nm to σ=2.5μm, we quantify the effect of the nanofocus on the small-angle scattering lineshape and on the diffusion coefficients obtained from nano-XPCS. We observe that the use of nanobeams leads to a multifold increase in speckle contrast, which greatly improves the experimental signal-to-noise ratio, quantified from the two-time intensity correlation functions. We conclude that it is possible to account for influence of the high beam divergence on the lineshape and measured dynamics by including a convolution with the nanobeam profile in the model.

The absence of stray fields, their insensitivity to external magnetic fields, and ultrafast dynamics make antiferromagnets promising candidates for active elements in spintronic devices. Here, we demonstrate manipulation of the Néel vector in the metallic collinear antiferromagnet Mn2Au by combining strain and femtosecond laser excitation. Applying tensile strain along either of the two in-plane easy axes and locally exciting the sample by a train of femtosecond pulses, we align the Néel vector along the direction controlled by the applied strain. The dependence on the laser fluence and strain suggests the alignment is a result of optically triggered depinning of 90° domain walls and their motion in the direction of the free energy gradient, governed by the magneto-elastic coupling. The resulting, switchable state is stable at room temperature and insensitive to magnetic fields. Such an approach may provide ways to realize robust high-density memory device with switching time scales in the picosecond range. 

X-ray free-electron lasers (XFELs) with megahertz repetition rate can provide novel insights into structural dynamics of biological macromolecule solutions. However, very high dose rates can lead to beam-induced dynamics and structural changes due to radiation damage. Here, we probe the dynamics of dense antibody protein (Ig-PEG) solutions using megahertz X-ray photon correlation spectroscopy (MHz-XPCS) at the European XFEL. By varying the total dose and dose rate, we identify a regime for measuring the motion of proteins in their first coordination shell, quantify XFEL-induced effects such as driven motion, and map out the extent of agglomeration dynamics. The results indicate that for average dose rates below 1.06 kGy μs⁻¹ in a time window up to 10 μs, it is possible to capture the protein dynamics before the onset of beam induced aggregation. We refer to this approach as correlation before aggregation and demonstrate that MHz-XPCS bridges an important spatio-temporal gap in measurement techniques for biological samples.