Enabling time-resolved 2D spatial-coherence measurements using the Fourier-analysis method with an integrated curved-grating beam monitor

Direct 2D spatial-coherence measurements are increasingly gaining importance at synchrotron beamlines, especially due to present and future upgrades of synchrotron facilities to diffraction-limited storage rings. We present a method to determine the 2D spatial coherence of synchrotron radiation in a direct and particularly simple way by using the Fourier-analysis method in conjunction with curved gratings. Direct photon-beam monitoring provided by a curved grating circumvents the otherwise necessary separate determination of the illuminating intensity distribution required for the Fourier-analysis method. Hence, combining these two methods allows for time-resolved spatial-coherence measurements. As a consequence, spatial-coherence degradation effects caused by beamline optics vibrations, which is one of the key issues of state-of-the-art X-ray imaging and scattering beamlines, can be identified and analyzed. © 2020 Optical Society of America

Discovery of Superconductivity and Electron-Phonon Drag in the Non-Centrosymmetric Semimetal LaRhGe3_3

We present a comprehensive study of the non-centrosymmetric semimetal LaRhGe$_3$. Our transport measurements reveal evidence for electron-hole compensation at low temperatures, resulting in a large magnetoresistance of 3000% at 1.8 K and 14 T. The carrier concentration is on the order of $10^{21}\rm{/cm}^3$, higher than typical semimetals. We predict theoretically the existence of $\textit{almost movable}$ Weyl nodal lines that are protected by the tetragonal space group. We discover superconductivity for the first time in this compound with a $T_{\text c}$ of 0.39(1) K and $B_{\rm{c}}(0)$ of 2.1(1) mT, with evidence from specific heat and transverse-field muon spin relaxation ($\mu \rm{SR}$). LaRhGe$_3$ is a weakly-coupled type-I superconductor, and we find no evidence for time-reversal symmetry breaking in our zero-field $\mu \rm{SR}$. We study the electrical transport in the normal state and find an unusual $\sim T^{3}$ dependence at low temperature while Seebeck coefficient and thermal conductivity measurements reveal a peak in the same temperature range. We conclude that the transport properties of LaRhGe$_3$ in its normal state are strongly influenced by electron-phonon interactions. Furthermore, we examine the temperature dependent Raman spectra of LaRhGe$_3$ and find that the lifetime of the lowest energy $A_1$ phonon is dominated by phonon-electron scattering instead of anharmonic decay

A vision transformer architecture for the automated segmentation of retinal lesions in spectral domain optical coherence tomography images

Abstract Neovascular age-related macular degeneration (nAMD) is one of the major causes of irreversible blindness and is characterized by accumulations of different lesions inside the retina. AMD biomarkers enable experts to grade the AMD and could be used for therapy prognosis and individualized treatment decisions. In particular, intra-retinal fluid (IRF), sub-retinal fluid (SRF), and pigment epithelium detachment (PED) are prominent biomarkers for grading neovascular AMD. Spectral-domain optical coherence tomography (SD-OCT) revolutionized nAMD early diagnosis by providing cross-sectional images of the retina. Automatic segmentation and quantification of IRF, SRF, and PED in SD-OCT images can be extremely useful for clinical decision-making. Despite the excellent performance of convolutional neural network (CNN)-based methods, the task still presents some challenges due to relevant variations in the location, size, shape, and texture of the lesions. This work adopts a transformer-based method to automatically segment retinal lesion from SD-OCT images and qualitatively and quantitatively evaluate its performance against CNN-based methods. The method combines the efficient long-range feature extraction and aggregation capabilities of Vision Transformers with data-efficient training of CNNs. The proposed method was tested on a private dataset containing 3842 2-dimensional SD-OCT retina images, manually labeled by experts of the Franziskus Eye-Center, Muenster. While one of the competitors presents a better performance in terms of Dice score, the proposed method is significantly less computationally expensive. Thus, future research will focus on the proposed network’s architecture to increase its segmentation performance while maintaining its computational efficiency

Quenching of the Resonant Magnetic Scattering by Ultra-Short Free-Electron Laser Pulses

With the advent of free-electron lasers (FELs), new opportunities haveemerged for studying dynamics in matter on ultra-fast time and ultra-shortlength scales simultaneously. As one of the forefront topics within contemporaryresearch on magnetism, studies of ultrafast laser-induced magnetizationdynamics [1] have benefited from these recent developments – revealinga nanoscale spatial response in a domain system coupled to the demagnetizationprocess [2] or transfer of angular momentum between two magneticcompounds in an inhomogeneous magnetic alloy [3]. Such studies of magnetizationdynamics rely on achieving magnetic scattering contrast through theX-ray magnetic circular dichroism (XMCD) effect by tuning the incidentphoton energy resonantly to one of the dichroic M or L absorption edges ofthe magnetic element. However, at extreme FEL fluences, a quenching ofthe resonant magnetic scattering signal was recently observed [4], indicatingthat the FEL radiation does not only act as a probe but also strongly interactswith the sample, effectively altering it already on a time scale shorter thanthe pulse duration of 70 fs. Here, we report on resonant magnetic small-angleX-ray scattering (mSAXS) experiments at the cobalt M3-edge, performed onCo/Pt multilayers with perpendicular magnetic anisotropy showing 100-nmscale magnetic domain patterns, with the purpose of investigating the FELfluence dependence of the resonant magnetic scattering signal. Our results(Figure 1) show a significant reduction (quenching) of the magnetic scatteringstrength with increasing FEL fluence. The intra-pulse quenchingeffect already sets in at much lower fluences than previously expected,revealing the violation of the credo ‘diffract before destruct’ already forthe low fluence regime where the sample is not destroyed by a single-pulseirradiation

Anomalous thermal conductivity of alkaline-earth-metal-substituted EuTiO3 induced by resonant scattering

We have investigated thermal conductivities (κ) of polycrystalline Eu1–xAxTiO3 (A = Ca, Sr, Ba, 0 ≤ x ≤ 0.8) bulk materials in the temperature range of ∼ 2 K < T < 1173 K. The EuTiO3 demonstrates anomalous glass-like κ(T) behavior at low temperatures. Partial substitutions with Sr2+ and Ba2+ do not cause a significant change in the κ(T) behavior, while a κ(T) peak, which looks like a manifestation of a typical crystalline solid, appears only in the Ca-substituted samples with an orthorhombic structure when x ≥ 0.4. After excluding the magnetic effects on κ and discussing the possible phonon scattering mechanisms in depth, together with heat capacity Cp measurements and high-resolution X-Ray diffraction characterization, we find that the unusual low κ at low temperatures is attributed to resonant scattering induced by the intrinsic disordered local structure and lattice instability in EuTiO3. Due to the different lattice dynamics of ATiO3, the lattice structure of Eu1–xCaxTiO3 can be regarded as formed by a part-soft (from EuTiO3) part-rigid (from CaTiO3) sublattice. The anomalous κ(T) behavior of Eu1–xCaxTiO3 results from the combined effect of phonon transport between the normal phononic heat transport in the rigid sublattice and the strong damping of heat conduction in the soft sublattice

Quenching of the Resonant Magnetic Scattering by Ultra-Short Free-Electron Laser Light Pulses

The new free-electron laser (FEL) sources provide radiation with unprecedentedparameters in terms of ultrashort pulse length, high photonflux, and coherence. These properties make FELs ideal tools forstudying ultrafast dynamics in matter on a previously inaccessiblelevel. Yet, FELs do not only probe matter, but can also drive it inhighly excited states which are otherwise inaccessible.Here, we report on a resonant magnetic scattering experiment, wherethe focussed FEL light pulses probe the magnetic domain system of athin magnetic film. Both, single and double FEL pulses at differentfluences are used to follow the quenching of the resonant scatteringefficiency