Driving magnetic order in a manganite by ultrafast lattice excitation

Optical control of magnetism, of interest for high-speed data processing and storage, has only been demonstrated with near-infrared excitation to date. However, in absorbing materials, such high photon energies can lead to significant dissipation, making switch back times long and miniaturization challenging. In manganites, magnetism is directly coupled to the lattice, as evidenced by the response to external and chemical pressure, or to ferroelectric polarization. Here, femtosecond mid-infrared pulses are used to excite the lattice in La0.5Sr1.5MnO4 and the dynamics of electronic order are measured by femtosecond resonant soft x-ray scattering with an x-ray free electron laser. We observe that magnetic and orbital orders are reduced by excitation of the lattice. This process, which occurs within few picoseconds, is interpreted as relaxation of the complex charge-orbital-spin structure following a displacive exchange quench - a prompt shift in the equilibrium value of the magnetic and orbital order parameters after the lattice has been distorted. A microscopic picture of the underlying unidirectional lattice displacement is proposed, based on nonlinear rectification of the directly-excited vibrational field, as analyzed in the specific lattice symmetry of La0.5Sr1.5MnO4. Control of magnetism through ultrafast lattice excitation has important analogies to the multiferroic effect and may serve as a new paradigm for high-speed optomagnetism.Comment: 10 pages manuscript, 4 figure

Vorkommen, Nachweis und Bestimmung von 2-und 3-Methyl-2,3-dihydroxybuttersäure und 2-Hydroxy-glutarsäure im Wein

Die als Gärungsnebenprodukt im Wein auftretende 2-Methyl-2,3-dihydroxybuttersäure wurde von der sich papierchromatographisch ähnlich verhaltenden Milchsäure in geeigneten Laufmitteln abgetrennt und über die bei der Perjodatoxydation in stöchiometrischer Menge erhaltenen Spaltprodukte Acetaldehyd und Brenztraubensäure identifiziert und quantitativ bestimmt. Untersuchungen zur Kon-figurationsaufklärung ergaben, daß 2-MDHBS im Wein in der Anglycerinsäure genannten Threo-Form vorliegt.2-MDHBS stört die Milchsäurebestimmung nach REBULEIN, jedoch scheint die dadurch bedingte Ungenauigkeit aufgrund der bisher gefundenen geringen Mengen unerheblich zu sein.Die von anderen Autoren im Wein gefundene 3-Methyl-2,3-dihydroxybuttersäure konnte dagegen nicht nachgewiesen werden. Als weiteres Gärungsnebenprodukt wurde 2-Hydroxyglutarsäure und deren Lacton isoliert.Nach Fertigstellung des Manuskriptes erschienen 3 Arbeiten von MÖHLER und PIRES (24, 25, 26), in denen ebenfalls über das Vorkommen von Anglycerinsäure im Wein berichtet wird. Ausgehend von den Ergebnissen der kernresonanzspektroskopischen Untersuchungen von LAYOLE et al. (27) wird die Anglycerinsäure darin als die in der Erythro-Konfiguration vorliegende 2-MDHBS bezeichnet. Nach eingehenden Überlegungen sind wir zu der Ansicht gelangt, daß durch den von LAYOLE erbrachten Identitätsbeweis unsere Befunde, die zu der gegenteiligen Identifizierung führten und die im wesentlichen auf der spezifischen Darstellung der Erythro-Verbindung aus Tiglinsäure durch OsO4-0xydation beruhen, unberührt bleiben. Wir möchten daher bis zu einer erneuten Überprüfung die Identifizierung der Konfiguration insgesamt in Frage stellen. Zur Bestimmung der Anglycerinsäure wurden von MÖHLER und PIRES die durch Chromatographie an einer Silikagelsäule von anderen Weinbestandteilen getrennten und gereinigten Substanzen mit Perjodat umgesetzt und danach jodometrisch titriert. Es wurden auf diese Weise 60-525 mg/l, im Mittel ca. 220 mg/l Anglycerinsäure im Wein festgestellt. Diese Werte liegen beträchtlich über den von uns gefundenen Mengen. Ob diese Differenzen analytisch oder substratbedingt sind, ist vorerst nicht bekannt. Ebenfalls nach Fertigstellung des Manuskriptes erschien eine Arbeit von CASTINO (28), in der über 2-MDHBS-Gehalte im Wein berichtet wird, die zwischen 52 und 144 mg/1 (Mittelwert 92 mg/l) liegen und damit mit den von uns gefundenen Werten gut übereinstimmen

Magnetic switching in granular FePt layers promoted by near-field laser enhancement

Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle x-ray scattering at an x-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, one order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between "up" and "down" magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material, with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. The fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer

BCAT1 redox function maintains mitotic fidelity

The metabolic enzyme branched-chain amino acid transaminase 1 (BCAT1) drives cell proliferation in aggressive cancers such as glioblastoma. Here, we show that BCAT1 localizes to mitotic structures and has a non-metabolic function as a mitotic regulator. Furthermore, BCAT1 is required for chromosome segregation in cancer and induced pluripotent stem cells and tumor growth in human cerebral organoid and mouse syngraft models. Applying gene knockout and rescue strategies, we show that the BCAT1 CXXC redox motif is crucial for controlling cysteine sulfenylation specifically in mitotic cells, promoting Aurora kinase B localization to centromeres, and securing accurate chromosome segregation. These findings offer an explanation for the well-established role of BCAT1 in promoting cancer cell proliferation. In summary, our data establish BCAT1 as a component of the mitotic apparatus that safeguards mitotic fidelity through a moonlighting redox functionality

An assessment of the resolution limitation due to radiation-damage in x-ray diffraction microscopy

X-ray diffraction microscopy (XDM) is a new form of x-ray imaging that is being practiced at several third-generation synchrotron-radiation x-ray facilities. Although only five years have elapsed since the technique was first introduced, it has made rapid progress in demonstrating high-resolution threedimensional imaging and promises few-nm resolution with much larger samples than can be imaged in the transmission electron microscope. Both life- and materials-science applications of XDM are intended, and it is expected that the principal limitation to resolution will be radiation damage for life science and the coherent power of available x-ray sources for material science. In this paper we address the question of the role of radiation damage. We use a statistical analysis based on the so-called "dose fractionation theorem" of Hegerl and Hoppe to calculate the dose needed to make an image of a lifescience sample by XDM with a given resolution. We conclude that the needed dose scales with the inverse fourth power of the resolution and present experimental evidence to support this finding. To determine the maximum tolerable dose we have assembled a number of data taken from the literature plus some measurements of our own which cover ranges of resolution that are not well covered by reports in the literature. The tentative conclusion of this study is that XDM should be able to image frozen-hydrated protein samples at a resolution of about 10 nm with "Rose-criterion" image quality.Comment: 9 pages, 4 figure