Publikationen

Literatur

Foto: pixabay
Literatur

27 Publikationen filtern

Die Publikationen filtern

Hervorgehobene Autoren sind Mitglieder der Forschungsgruppe.

  1. Phonon Engineering in Ultrathin Sn Films

    Autoren
    S. Velten, K. Schlage, I. Sergeev, O. Leupold, R. Steinbrügge, V. Reddy, M. Hu, E. Alp, L. Bocklage, R. Röhlsberger
    Erscheinungsjahr
    Erschienen in:
    Advanced Materials Interfaces
    Nanostructuring offers unique opportunities to manipulate vibrational properties of materials through reduced dimensionality. This is widely exploited in materials science to engineer thermal conductivity in nanostructures, for example. Similarly, in quantum optics, nanoscale engineering of vibrational states can suppress thermal decoherence and enhance coherent light–matter interactions. In x-ray quantum optics, vibrational properties are especially critical because light–matter interaction often occurs via coherent excitations of ultrasharp nuclear resonances, requiring a recoilless interaction, i.e., no energy exchange between nuclei and lattice. This raises the question: can nanoscale engineering also enhance coherent light–matter interactions in x-ray quantum optics, and thereby enable the use of nuclear resonances with typically low recoilless interaction fractions, such as the (Formula presented.) resonance of (Formula presented.). Here, we demonstrate the tunability of the vibrational properties of nanometer-thin Sn films by embedding them in multilayer structures, achieving nearly an order-of-magnitude increase in the recoilless fraction. Using nuclear inelastic x-ray scattering, we studied vibrational density of states of Sn layers with respect to interlayer diffusion, structural disorder and interfacial intermetallic compound formation. Our results show that suitable embedding materials can substantially modify Sn's vibrational behavior and thus potentially enable the (Formula presented.) nuclear resonance for x-ray quantum optics applications.
    Universitätsbibliographie Jena:
    fsu_mods_00035179Externer Link

  2. Interferometric measurement of nuclear resonant phase shift with a nanoscale Young double waveguide

    Autoren
    L. Lohse, A. Negi, M. Osterhoff, P. Meyer, S. Yaroslavtsev, A. Chumakov, L. Bocklage, R. Röhlsberger, T. Salditt
    Erscheinungsjahr
    Erschienen in:
    Nature Photonics
    The phase shift of an electromagnetic wave, imprinted by its interaction with atomic scatterers, is a central quantity in optics and photonics. In particular, it encodes information about optical resonances and photon–matter interaction. Although being a routine task in the optical regime, interferometric measurements of phase shifts in the X-ray frequency regime are notoriously challenging due to the short wavelengths and associated stability requirements. As a result, existing X-ray interferometers are ill-suited for light confined to the nanometre scale. Here we demonstrate a nanoscale interferometer, inspired by Young’s double-slit experiment, to measure the dispersive phase shift due to the 14.4-keV nuclear resonance of the Mössbauer isotope 57Fe coupled to an X-ray waveguide. From the single-photon interference patterns, we precisely extract the phase shifts in the vicinity of the nuclear resonance resolved in photon energy by using Bayesian inference. We find that the combined information from phase shift and absorbance reveals microscopic coupling parameters, which are not accessible from the absorption measurements alone. The demonstrated principle lays the basis for integrated X-ray interferometric sensors.
    Universitätsbibliographie Jena:
    fsu_mods_00035771Externer Link

  3. Revealing charge anisotropies in metal compounds via high-purity x-ray polarimetry

    Autoren
    L. Scherthan, J. Wolny, I. Faus, O. Leupold, K. Schulze, S. Höfer, R. Loetzsch, B. Marx-Glowna, C. Anson, A. Powell, I. Uschmann, H. Wille, G. Paulus, V. Schünemann, R. Röhlsberger
    Erscheinungsjahr
    Erschienen in:
    Physical review research
    Linear polarization analysis of hard x-rays is employed to probe electronic anisotropies in metal-containing complexes with high selectivity. We use polarization-resolved nuclear forward scattering (PR-NFS) of synchrotron radiation at the 14.4 keV nuclear resonance of Fe ₅₇ to determine electric field gradients (EFGs) in an iron(II) spin-crossover compound as they evolve during a temperature-dependent high-spin/low-spin transition. A pair of crossed Si(840) channel-cut crystals provides a high-purity x-ray polarimeter that suppresses the nonresonant background by nearly nine orders of magnitude and enables selective detection of nuclear resonant σ→π scattering. Using the spin-crossover complex Fe(PM-BiA) ₂ (NCS) ₂ as a model system, we determine the orientation of the EFG tensor in the high-spin and low-spin states and follow its reorientation across the gradual thermally driven spin transition. By choosing suitable sample orientations, the polarization selectivity enhances the signal of a high-spin minority fraction of a few percent at low temperature. It reveals that the high-spin EFG at 120 K is not randomly distributed and does not align with the dominant low-spin EFG when these high-spin centers form a minority phase embedded in a low-spin matrix. The combination of PR-NFS with dynamical NFS simulations and density-functional calculations thus provides a sensitive, element- and site-selective method to quantify electronic anisotropies and their changes across phase transitions in Mössbauer-active metal compounds.
    Universitätsbibliographie Jena:
    fsu_mods_00037244Externer Link

  4. Mechanical Stress Evolution in Polycrystalline Ge Thin Films Under MeV Ion Irradiation

    Autoren
    K. Paz Corrales, A. Reupert, K. Lubig, F. Müller, B. Marx-Glowna, R. Röhlsberger, T. Weickhardt, G. Soavi, M. Hafermann, E. Wendler, C. Ronning
    Erscheinungsjahr
    Erschienen in:
    Advanced Materials Interfaces
    Ion irradiation is a powerful tool for modifying the electrical and optical properties of device-relevant heterostructures, but it also induces mechanical stress that can degrade or—if controlled—enhance performance. We investigated in situ the stress evolution in polycrystalline Ge films irradiated with 1.8 MeV Au ions across wide fluences. Three distinct regimes emerge. At low ion fluences, defect-induced lattice expansion compensates initial deposition-induced tensile stress, bringing films to near-zero stress. The defects can migrate toward grain boundaries, which act as effective sinks, promoting recombination and enhancing irradiation resistance, thereby delaying amorphization compared to single-crystalline Ge. At intermediate fluences, defect accumulation drives crystalline-to-amorphous transition with increasing tensile stress, confirmed by post-irradiation X-ray diffraction and Raman spectroscopy. At high fluences, stress partially relaxes due to swelling, plastic deformation or interface effects. Our results demonstrate controlled ion-irradiation induced stress tuning in poly-Ge/fused-silica systems, indicating the key role of microstructure, and thus yield criteria for stress engineering in Ge-based optoelectronic and CMOS-based devices.
    Universitätsbibliographie Jena:
    fsu_mods_00035904Externer Link

  5. Energy–time ptychography for one-dimensional phase retrieval

    Autoren
    A. Negi, L. Lohse, S. Velten, I. Sergeev, O. Leupold, S. Sadashivaiah, D. Bessas, A. Chumakhov, C. Brandt, L. Bocklage, G. Meier, R. Röhlsberger
    Erscheinungsjahr
    Erschienen in:
    Optica
    Phase retrieval is at the heart of adaptive optics and modern high-resolution imaging. Without phase information, optical systems are limited to intensity-only measurements, hindering full reconstruction of object structures and wavefront dynamics essential for advanced applications. Here, we address a one-dimensional phase problem linking energy and time, which arises in X-ray scattering from ultrasharp nuclear resonances. We leverage the Mössbauer effect, where nuclei scatter radiation without energy loss to the lattice and are sensitive to their magneto-chemical environments. Rather than using traditional spectroscopy with radioactive gamma-ray sources, we measure nuclear forward scattering of synchrotron X-ray pulses in the time domain, providing superior sensitivity and faster data acquisition. Extracting spectral information from a single measurement is challenging due to the missing phase information, typically requiring extensive modeling. Instead, we use multiple energetically overlapping measurements to retrieve both the transmission spectrum and the phase of the scattering response, similar to ptychographic phase retrieval in imaging. Our robust approach can overcome the bandwidth limitations of gamma-ray sources, opening new research directions, to the best of our knowledge, with modern X-ray sources and Mössbauer isotopes.
    Universitätsbibliographie Jena:
    fsu_mods_00028233Externer Link

  6. Collective Nuclear Excitation and Pulse Propagation in Single-Mode X-Ray Waveguides

    Autoren
    L. Lohse, P. Andrejić, S. Velten, M. Vassholz, C. Neuhaus, A. Negi, A. Panchwanee, I. Sergeev, A. Pálffy, T. Salditt, R. Röhlsberger
    Erscheinungsjahr
    Erschienen in:
    Physical review letters
    Waveguides offer a means to controllably couple atomic ensembles to the electromagnetic field therein. Here, we demonstrate x-ray propagation in planar thin-film waveguides coupled to Mössbauer nuclei under collective resonant excitation by short pulses of synchrotron radiation. We record x-ray photons that have been emitted into resonant modes of the waveguide. Depending on the geometry and mode of excitation, two fundamentally different signatures of the collective emission are observed, for which we present a unifying theoretical model. Our results form a new platform for waveguide quantum electrodynamics in the hard x-ray regime with the potential to provide a coherent narrow band source of x-rays on the nanometer scale.
    Universitätsbibliographie Jena:
    fsu_mods_00027078Externer Link

  7. Towards a vacuum birefringence experiment at the Helmholtz International Beamline for Extreme Fields (Letter of Intent of the BIREF@HIBEF Collaboration)

    Autoren
    N. Ahmadiniaz, C. Bähtz, A. Benediktovitch, C. Bömer, L. Bocklage, T. Cowan, J. Edwards, S. Evans, S. Franchino Viñas, H. Gies, S. Göde, J. Görs, J. Grenzer, U. Hernandez Acosta, T. Heinzl, P. Hilz, W. Hippler, L. Huang, O. Humphries, F. Karbstein, P. Khademi, B. King, T. Kluge, C. Kohlfürst, D. Krebs, A. Laso-García, R. Lötzsch, A. Macleod, B. Marx-Glowna, E. Mosman, M. Nakatsutsumi, G. Paulus, S. Rahul, L. Randolph, R. Röhlsberger, N. Rohringer, A. Sävert, S. Sadashivaiah, R. Sauerbrey, H. Schlenviogt, S. Schmidt, U. Schramm, R. Schützhold, J. Schwinkendorf, D. Seipt, M. Šmíd, T. Stöhlker, T. Toncian, M. Valialshchikov, A. Wipf, U. Zastrau, M. Zepf
    Erscheinungsjahr
    Erschienen in:
    High Power Laser Science and Engineering
    Quantum field theory predicts a nonlinear response of the vacuum to strong electromagnetic fields of macroscopic extent. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. A particularly distinct signature of the resulting optical activity of the quantum vacuum is vacuum birefringence. This offers an excellent opportunity for a precision test of nonlinear quantum electrodynamics in an uncharted parameter regime. Recently, the operation of the high-intensity Relativistic Laser at the X-ray Free Electron Laser provided by the Helmholtz International Beamline for Extreme Fields has been inaugurated at the High Energy Density scientific instrument of the European X-ray Free Electron Laser. We make the case that this worldwide unique combination of an X-ray free-electron laser and an ultra-intense near-infrared laser together with recent advances in high-precision X-ray polarimetry, refinements of prospective discovery scenarios and progress in their accurate theoretical modelling have set the stage for performing an actual discovery experiment of quantum vacuum nonlinearity.
    Universitätsbibliographie Jena:
    fsu_mods_00023233Externer Link

  8. Proof-of-principle experiment for the dark-field detection concept for measuring vacuum birefringence

    Autoren
    M. Šmíd, P. Khademi, N. Ahmadiniaz, M. Andrzejewski, C. Baehtz, E. Brambrink, J. Bulička, T. Burian, S. Cafiso, J. Chalupský, T. Cowan, S. Göde, J. Grenzer, V. Hájková, P. Hilz, W. Hippler, H. Höppner, A. Horynová, L. Huang, O. Humphries, Š. Jelínek, L. Juha, F. Karbstein, C. Kohlfürst, A. Garcia, R. Lötzsch, M. Masruri, A. Matheron, M. Nakatsutsumi, G. Paulus, A. Pelka, T. Preston, S. Rahul, L. Randolph, A. Sävert, H. Schlenvoigt, R. Schützhold, J. Schwinkendorf, T. Stöhlker, M. Toncian, T. Toncian, M. Valialshchikov, V. Vozda, E. Weckert, C. Wessel, J. Wild, U. Zastrau, M. Zepf
    Erscheinungsjahr
    Erschienen in:
    Physical Review A
    Vacuum fluctuations give rise to effective nonlinear interactions between electromagnetic fields. These generically modify the characteristics of light traversing a strong-field region. X-ray free-electron lasers (XFELs) constitute a particularly promising probe, due to their brilliance, the possibility of precise control and favorable frequency scaling. However, the nonlinear vacuum response is very small even when probing a tightly focused high-intensity laser field with XFEL radiation and direct measurement of light-by-light scattering of real photons and the associated fundamental physics constants of the quantum vacuum has not been possible to date. Achieving a sufficiently good signal-to-background separation is key to a successful quantum vacuum experiment. To master this challenge, a dark-field detection concept has recently been proposed. Here we present the results of a proof-of-principle experiment validating this approach by demonstrating that using real-world x-ray optics the background signal can be suppressed sufficiently to measure the weak nonlinear response of the vacuum.
    Universitätsbibliographie Jena:
    fsu_mods_00030072Externer Link

  9. Nuclear quantum memory for hard x-ray photon wave packets

    Autoren
    S. Velten, L. Bocklage, X. Zhang, K. Schlage, A. Panchwanee, S. Sadashivaiah, I. Sergeev, O. Leupold, A. Chumakov, O. Kocharovskaya, R. Röhlsberger
    Erscheinungsjahr
    Erschienen in:
    Science advances
    Universitätsbibliographie Jena:
    fsu_mods_00014445Externer Link

  10. TEMPUS, a Timepix4-based system for the event-based detection of X-rays

    Autoren
    J. Correa, A. Ignatenko, D. Pennicard, S. Lange, S. Fridman, S. Karl, L. Lohse, B. Senfftleben, I. Sergeev, S. Velten, D. Prajapat, L. Bocklage, H. Bromberger, A. Samartsev, A. Chumakov, R. Rüffer, J. von Zanthier, R. Röhlsberger, H. Graafsma
    Erscheinungsjahr
    Erschienen in:
    Journal of synchrotron radiation
    TEMPUS is a new detector system being developed for photon science. It is based on the Timepix4 chip and, thus, it can be operated in two distinct modes: a photon-counting mode, which allows for conventional full-frame readout at rates up to 40 kfps; and an event-driven time-stamping mode, which allows excellent time resolution in the nanosecond regime in measurements with moderate X-ray flux. In this paper, the initial prototype, a single-chip device, is introduced, and the readout system described. Moreover, and in order to evaluate its capabilities, some tests were performed at PETRA III and ESRF for which results are also presented.
    Universitätsbibliographie Jena:
    fsu_mods_00016752Externer Link

  11. ¹⁹³Ir nuclear forward scattering of an iridium(I) complex

    Autoren
    M. Hoock, O. Leupold, A. Haag, A. Omlor, R. Steinbrügge, I. Sergueev, R. Röhlsberger, H. Krüger, J. Wolny, V. Schünemann
    Erscheinungsjahr
    Erschienen in:
    Hyperfine Interactions: journal devoted to research in the border regions of solid state, atomic and nuclear physics
    Synchrotron based nuclear forward scattering (NFS) experiments using the ¹⁹³Ir nucleus have been performed for the first time on a dinuclear iridium(I) complex, [IrCl(COD)]₂ with COD being cycloocta-1,5-diene. This complex serves as a catalyst for hydrogenation and other chemical reactions. Both, the obtained absolute values of the isomer shift δ=0.87mm s-1 and the quadrupole splitting ΔEQ=3.82mm s-1 agree within the experimental error with values obtained via conventional ¹⁹³Ir Mössbauer spectroscopy reported earlier (Gál M. et al. J. Radioanal. Nucl. Chem., 260 (1) 2004, 133). In addition, we present density functional theory (DFT) calculations of the complex yielding its electronic structure and related Mössbauer parameters.
    Universitätsbibliographie Jena:
    fsu_mods_00009473Externer Link
Paginierung Seite 1