Search NASA⌕ Search

Engineering topics

Schoenlein, R. W.

Publications and source records attributed to Schoenlein, R. W..

15 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Polaronic effect in the x-ray absorption spectra of La 1- x Ca x MnO 3 manganites

X-ray absorption spectroscopy (XAS) is performed to study changes in the electronic structures of colossal magnetoresistance (CMR) and charged ordered (CO) La 1–x Ca x MnO 3 manganites with respect to temperature. The pre-edge features in O and Mn K-edge XAS spectra, which are highly sensitive to the local distortion of MnO 6 octahedral, exhibit contrasting temperature dependence between CMR and CO samples. The seemingly counter-intuitive XAS temperature dependence can be reconciled in the context of polarons. Furthermore these results help identify the most relevant orbital states associated with polarons and highlight the crucial role played by polarons in understanding the electronic structures of manganites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Nonlinear Ultrafast Spin Scattering in the Skyrmion Phase of Cu 2 OSeO 3

Ultrafast x-ray scattering studies of the topological Skyrmion phase in Cu 2 OSeO 3 show the dynamics to be strongly dependent on the excitation energy and fluence. At high photon energies, where the electron-spin scattering cross section is relatively high, the excitation of the topological Skyrmion phase shows a nonlinear dependence on the excitation fluence, in contrast to the excitation of the conical phase which is linearly dependent on the excitation fluence. Finally, the excitation of the Skyrmion order parameter is nonlinear in the magnetic excitation resulting from scattering during electron-hole recombination, indicating different dominant scattering processes in the conical and Skyrmion phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The Linac Coherent Light Source: Recent Developments and Future Plans

The development of X-ray free-electron lasers (XFELs) has launched a new era in X-ray science by providing ultrafast coherent X-ray pulses with a peak brightness that is approximately one billion times higher than previous X-ray sources. The Linac Coherent Light Source (LCLS) facility at the SLAC National Accelerator Laboratory, the world’s first hard X-ray FEL, has already demonstrated a tremendous scientific impact across broad areas of science. Here in this paper, a few of the more recent representative highlights from LCLS are presented in the areas of atomic, molecular, and optical science; chemistry; condensed matter physics; matter in extreme conditions; and biology. This paper also outlines the near term upgrade (LCLS-II) and motivating science opportunities for ultrafast X-rays in the 0.25–5 keV range at repetition rates up to 1 MHz. Future plans to extend the X-ray energy reach to beyond 13 keV (<1 Å) at high repetition rate (LCLS-II-HE) are envisioned, motivated by compelling new science of structural dynamics at the atomic scale.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

The prominent role of oxygen in the multiferroicity of DyMnO3 and TbMnO3: a resonant soft x-ray scattering spectroscopy study

Oxygen is known to play an important role in the multiferroicity of rare earth manganites; however, how this role changes with rare earth elements is still not fully understood. To address this question, we have used resonant soft x-ray scattering spectroscopy to study the F-type (0; ; 0) diffraction peak from the antiferromagnetic order in DyMnO 3 and TbMnO 3 . We focus on the measurements at O K-edge of these two manganites, supplemented by the results at Mn L2- and Dy M5-edge of DyMnO 3 . We show that the electronic states of di erent elements are coupled more strongly in DyMnO 3 than in TbMnO 3 , presumably due to the stronger lattice distortion and the tendency to develop E-type antiferromagnetism in the ferroelectric state that promote the orbital hybridization. We also show that the anomaly in the correlation length of (0; ; 0) peak in DyMnO 3 signifies the exchange interaction between Mn and rare earth spins, which is absent in TbMnO 3 . Our findings reveal the prominent role of oxygen orbitals in the multiferroicity of rare earth manganites and the distinct energetics between them.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Coupled skyrmion sublattices in Cu2OSeO3

We report the observation of a skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct skyrmion sub-lattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals . The skyrmion sublattices are rotated with respect to each other implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this Moir'e-like phase with a continuous phase transition. Our findings will open a new class of science involving manipulation of quantum topological states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Simulating Ru L 3 -Edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexes in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗