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Abstract: The β′-Gd2(MoO4)3 phase is one of the most well-known multiferroic materials, exhibiting both ferroelectricity and ferroelasticity under ambient conditions, with a complex temperature-pressure phase diagram. In this study, we review the pressure-dependent behavior of the RE2(MoO4)3 compound family (where RE ≡ Pr–Ho), which crystallizes in the β′-phase, with the β-phase being the paraelectric parent structure. Eu, Tb, and Ho molybdates were synthesized via solid-state reactions, ensuring the absence of impurities. High-pressure experiments at DIAMOND synchrotron revealed that the β′-phase persists at low-pressures. At approximately 2 GPa, new peaks emerged, which were refined as a mixture of the β′-phase, other rare-earth molybdates, and oxides, some of which have been detected in earlier stages of synthesis. The β′-phase became distorted with increasing pressure while coexisting with these new phases, whose average unit cell volume was found to lie between that of the β′-phase and the formed distorted phase. Ultimately, this multiphase crystalline decomposition acts as a precursor to pressure-induced amorphization, leading to a loss of long-range periodicity without complete loss of local order. The onsets of pressure-induced decomposition, distortion of the β′-phase and apparent amorphization increase as the ionic radius of the rare-earth element decreases. This scenario of irreversible structural disorder accumulated through phase coexistence is consistent with previous studies and resolves a debate persisting for over half a century.

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Abstract: A surfactant-like peptide (SLP) bearing six non-native 3-(4-pyridyl)-l-alanine (Pal) residues and a C-terminal arginine residue, Pal6R, is shown to exhibit pH-dependent self-assembly which arises from the acid–base properties of the Pal residue (pKa ∼ 5). At a native pH of 2.4, “polyelectrolyte” correlation hole scattering is observed due to the electrostatic repulsion of highly charged molecules. The scaling of the domain size with concentration agrees with theoretical predictions for weakly charged flexible polyelectrolytes in a semidilute solution. In contrast, twisted nanotapes are observed at pH 7. The nanotapes are shown to comprise β-sheet structures packed in interdigitated bilayers. Atomistic molecular dynamics (MD) simulations confirmed the bilayer structure of the nanotapes, with extensive hydrogen bonding, and a twisting tendency. The novel SLP can stabilize water-in-oil emulsions at pH 7, forming β-sheet bilayer structures at the water droplet interface. Pal6R represents a model polyelectrolyte system with additional self-assembly and emulsion stabilization properties at neutral pH.

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Abstract: Kagome materials are known for hosting emergent quantum phenomena driven by the interaction between different lattice, charge, and spin orders. Here, we present a detailed angle-resolved photoemission (ARPES), density functional theory (DFT), and x-ray magnetic circular dichroism (XMCD) study of the electronic and magnetic structure of 𝑅⁢Ti3⁢Bi4 (𝑅=Nd, Sm, Gd). ARPES and DFT demonstrate that the bulk electronic band structure is dominated by the hybridization of the Ti bands, and the weak electron-like pocket at Γ is identified as a surface state. The isotropic XAS profile of the 𝑀4,5 edge of the rare earth is consistent with the presence of the 𝑅3+ oxidation state. Using the XMCD sum rules, backed by the atomic-multiplet-theory calculations, we obtain the spin and orbital magnetic moments. The Ti 𝐿2,3-edge XMCD reveals the presence of a small magnetic moment in GdTi3⁢Bi4, presumably driven by the proximity of the Ti kagome layers to the zigzag chains of Gd, while the total magnetic moment of Gd is shared by the 𝑓 and 𝑑 electrons. Our combined XMCD, ARPES, and DFT study provides an important piece of information to understand the spin-flip transitions and anomalous Hall effect observed in the 𝑅⁢Ti3⁢Bi4 kagome metals.

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Abstract: A new class of 3rd generation, bimorph deformable, X-ray mirrors have been developed, which are UHV “bakeable” to 200°C and provide diffraction-limited performance for achromatic focusing and wavefront correction of high-intensity photon beams. Optical metrology was used to reduce slope errors to ∼ 42 nrad rms and height errors to ∼ 200 pm rms for concave, flat, and convex elliptical curvatures. Curved X-ray mirrors with slope errors < 50 nrad rms and height errors < 500 pm rms are required for nano-focusing and coherence applications at low-emittance synchrotron light and free electron laser facilities. In recent years, impressive technical progress has been made to fabricate fixed-curvature X-ray mirrors, approaching diffraction-limited performance. However, for many scientific applications, active optics with a deformable surface profile are required to intermittently change the focal distance or size of the X-ray beam, or to make fine adjustments to the X-ray wavefront. What we believe to be a new class of high-grade, actively deformable optics have been developed, which provide diffraction-limited performance for achromatic focusing and wavefront correction of X-ray beams. 3rd generation, bimorph deformable, X-ray mirrors have piezoelectric PZT actuators bonded to the silicon substrate using silver nano-particles. They can be safely thermally annealed to 200°C and are ultra-high vacuum compatible, making them suitable for a wide range of X-ray energies, including soft X-rays. We present a comprehensive optical metrology study of a 32-channel, 3rd generation bimorph mirror mounted in an opto-mechanical holder to assess suitability for routine beamline operation. Fizeau interferometry and slope profilometry were performed to characterize the range, drift, stability, repeatability, and resolution of bending. Voltages to individual electrodes were optimized to minimise surface errors, based on metrology feedback and a constrained, linear algebra solver. Slope errors of ∼ 42 nrad rms and height errors ∼ 200 pm rms were achieved for three different curvatures (concave, flat, and convex). Metrology testing also demonstrated the extreme resolution of bending (2 nm changes in the height profile by incrementally applying 0.1 V shifts to all piezo actuators) and long-term curvature stability of 0.1% rms over 16 hours. Hysteresis, creep, and short-term drift of the bimorph’s profile were observed, which will be the subject of future research.

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Abstract: The superconducting gap is a characteristic feature of high-𝑇c superconductors and provides crucial information on the pairing mechanism underlying high-temperature superconductivity. Here, we employ high-resolution resonant inelastic x-ray scattering (RIXS) at the Cu 𝐿3 edge to investigate the superconducting gap in the overdoped cuprate Bi2⁢Sr2⁢Ca2⁢Cu3⁢O10+𝛿 (𝑇c⁢=107K). By analyzing antisymmetrized, temperature-dependent RIXS spectra over a range of in-plane momentum transfers, we observe a clear suppression of low-energy spectral weight below 𝑇c, indicative of superconducting-gap formation. This suppression is most pronounced at small momentum transfers [ | | | 𝒒∥ | | | ≤0.18 r.l.u. (reciprocal lattice units)] and corresponds to a gap size of approximately 2⁢Δ0∼130 meV. Comparison with theoretical calculations of the momentum-dependent charge susceptibility supports a 𝑑-wave symmetry of the superconducting gap, while an isotropic 𝑠-wave gap fails to reproduce key experimental features. These findings establish RIXS as a powerful, bulk-sensitive probe of superconducting-gap symmetry and highlight its utility for studying materials beyond the reach of surface-sensitive techniques such as ARPES and STM.