Photon Polarization Precession Spectroscopy for High-Resolution Studies of Spinwaves

A new type of spectroscopy for high-resolution studies of spin waves that relies on resonant scattering of hard x-rays is introduced. The energy transfer in the scattering process is encoded in the precession of the polarization vector of the scattered photons. Thus, the energy resolution of such a spectroscopy is independent of the bandwidth of the probing radiation. The measured quantity resembles the intermediate scattering function of the magnetic excitations in the sample. At pulsed x-ray sources, especially x-ray lasers, the proposed technique allows to take single-shot spectra of the magnetic dynamics. The method opens new avenues to study low-energy non-equilibrium magnetic processes in a pump-probe setup.Comment: 5 pages, 2 figure

Bottom-up fabrication of highly ordered metal nanostructures by hierarchical self-assembly

In a hierarchical nanopatterning routine relying exclusively on self-assembly processes we combine crystal surface reconstruction, microphase separation of copolymers, and selective metal diffusion to produce monodisperse metal nanostructures in highly regular arrays covering areas of square centimeters. In-situ GISAXS during Fe nanostructure formation evidences the outstanding structural order in the self-assembling system and hints at possibilities of sculpting nanostructures by external process parameters. Thus, we demonstrate that nanopatterning via self-assembly is a competitive alternative to lithography-based routines, achieving comparable pattern regularity, feature size, and patterned areas with considerably reduced effort. The option for in-situ investigations during pattern formation, the possibility of customizing the nanostructure morphology, the capacity to pattern arbitrarily large areas with ultra-high structure densities, and the potential of addressing the nanostructures individually enable numerous applications, e.g., in high-density magnetic data storage, in functional nanostructured materials, e.g., for photonics or catalysis, or in sensing based on surface plasmon resonances.Comment: 21 pages, 9 figures, 1 tabl

Nuclear resonant surface diffraction

Nuclear resonant x-ray diffraction in grazing incidence geometry is used to determine the lateral magnetic configuration in a one-dimensional lattice of ferromagnetic nanostripes. During magnetic reversal, strong nuclear superstructure diffraction peaks appear in addition to the electronic ones due to an antiferromagnetic order in the nanostripe lattice. We show that the analysis of the angular distribution of the resonantly diffracted x-rays together with the time-dependence of the coherently diffracted nuclear signal reveals surface spin structures with very high sensitivity. This novel scattering technique provides a unique access to laterally correlated spin configurations in magnetically ordered nanostructures and, in perspective, also to their dynamics

Spin precession mapping at ferromagnetic resonance via nuclear resonant scattering

We probe the spin dynamics in a thin magnetic film at ferromagnetic resonance by nuclear resonant scattering of synchrotron radiation at the 14.4 keV resonance of $^{57}$Fe. The precession of the magnetization leads to an apparent reduction of the magnetic hyperfine field acting at the $^{57}$Fe nuclei. The spin dynamics is described in a stochastic relaxation model adapted to the ferromagnetic resonance theory by Smit and Beljers to model the decay of the excited nuclear state. From the fits of the measured data the shape of the precession cone of the spins is determined. Our results open a new perspective to determine magnetization dynamics in layered structures with very high depth resolution by employing ultrathin isotopic probe layers

Scientific Opportunities with an X-ray Free-Electron Laser Oscillator

An X-ray free-electron laser oscillator (XFELO) is a new type of hard X-ray source that would produce fully coherent pulses with meV bandwidth and stable intensity. The XFELO complements existing sources based on self-amplified spontaneous emission (SASE) from high-gain X-ray free-electron lasers (XFEL) that produce ultra-short pulses with broad-band chaotic spectra. This report is based on discussions of scientific opportunities enabled by an XFELO during a workshop held at SLAC on June 29 - July 1, 2016Comment: 21 pages, 12 figure

Quantum Imaging with Incoherently Scattered Light from a Free-Electron Laser

The advent of accelerator-driven free-electron lasers (FEL) has opened new avenues for high-resolution structure determination via diffraction methods that go far beyond conventional x-ray crystallography methods. These techniques rely on coherent scattering processes that require the maintenance of first-order coherence of the radiation field throughout the imaging procedure. Here we show that higher-order degrees of coherence, displayed in the intensity correlations of incoherently scattered x-rays from an FEL, can be used to image two-dimensional objects with a spatial resolution close to or even below the Abbe limit. This constitutes a new approach towards structure determination based on incoherent processes, including Compton scattering, fluorescence emission or wavefront distortions, generally considered detrimental for imaging applications. Our method is an extension of the landmark intensity correlation measurements of Hanbury Brown and Twiss to higher than second-order paving the way towards determination of structure and dynamics of matter in regimes where coherent imaging methods have intrinsic limitations

Electronic Quantum Coherence in Glycine Molecules Probed with Ultrashort X-ray Pulses in Real Time

Structural changes in nature and technology are driven by charge carrier motion. A process such as charge-directed reactivity that can be operational in radiobiology is more efficient, if energy transfer and charge motion proceeds along well-defined quantum mechanical pathways keeping the coherence and minimizing dissipation. The open question is: do long-lived electronic quantum coherences exist in complex molecules? Here, we use x-rays to create and monitor electronic wave packets in the amino acid glycine. The outgoing photoelectron wave leaves behind a positive charge formed by a superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced electronic coherence through the photoelectron emission from the sequential double photoionization processes. The observed sinusoidal modulation of the detected electron yield as a function of time clearly demonstrates that electronic quantum coherence is preserved for at least 25 femtoseconds in this molecule of biological relevance. The surviving coherence is detected via the dominant sequential double ionization channel, which is found to exhibit a phase shift as a function of the photoelectron energy. The experimental results agree with advanced ab-initio simulations.Comment: 54 pages, 11 figure

Nuclear condensed matter physics with synchrotron radiation: basic principles, methodology and applications

This book provides a comprehensive introduction to the growing field of nuclear condensed matter physics with synchrotron radiation, a technique which finds numerous applications in fields such as magnetism, physics of surfaces and interfaces, lattice dynamics and more. Due to the enormous brilliance of modern synchrotron radiation sources, the method is particularly suited for the investigation of low-dimensional structures such as thin films and nanoparticles. The use of isotopic probe layers, for example, allows one to determine magnetic and vibrational properties with very high spatial resolution; focusing techniques and x-ray interference effects lead to a very high sensitivity for smallest amounts of material. The book is written on an introductory level with many examples employed to illustrate the special experimental possibilities