A5082822192- High-pressure geophysics and materials
- Advanced X-ray Imaging Techniques
- Topological Materials and Phenomena
- Electronic and Structural Properties of Oxides
- Crystallography and Radiation Phenomena
- Laser-Matter Interactions and Applications
- Advanced Electron Microscopy Techniques and Applications
- Advanced Chemical Physics Studies
- Photorefractive and Nonlinear Optics
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Organic and Molecular Conductors Research
- Thermal properties of materials
- Thermography and Photoacoustic Techniques
- Phase-change materials and chalcogenides
- Transition Metal Oxide Nanomaterials
- Terahertz technology and applications
- Chalcogenide Semiconductor Thin Films
- Spectroscopy and Quantum Chemical Studies
- Solid-state spectroscopy and crystallography
- Physics of Superconductivity and Magnetism
- Electron and X-Ray Spectroscopy Techniques
- Nuclear Physics and Applications
- Semiconductor Quantum Structures and Devices
- Quantum, superfluid, helium dynamics
SLAC National Accelerator Laboratory
2015-2024
Stanford University
2010-2019
Linac Coherent Light Source
2014-2017
University of California, Santa Barbara
2017
University of Michigan
2005-2014
Stanford Synchrotron Radiation Lightsource
2014
University of Illinois Urbana-Champaign
2014
Universidad Católica Santo Domingo
2012
Balseiro Institute
2001-2002
Bariloche Atomic Centre
2001-2002
Many ultrafast solid phase transitions are treated as chemical reactions that transform the structures between two different unit cells along a reaction coordinate, but this neglects role of disorder. Although diffraction provides insights into atomic dynamics during such transformations, alone probes an averaged cell and is less sensitive to randomness in transition pathway. Using total scattering femtosecond x-ray pulses, we show disordering photoexcited vanadium dioxide (VO2) central...
Structural switch for fast switching Phase-change materials are important computer memory. They can quickly from glassy to crystalline using a thermal pulse and then lock in that structure long time at lower temperature. Zalden et al. probed the underlying atomic of two phase-change during this ultrafast x-rays simulations (see Perspective by Rao ). A liquid-liquid phase transition both allowed high temperatures. The lower-temperature glass locks structure, allowing long-term memory storage....
Abstract Crystal lattice fluctuations, which are known to influence phase transitions of quantum materials in equilibrium, also expected determine the dynamics light-induced changes. However, they have only rarely been explored these dynamical settings. Here we study time evolution fluctuations paraelectric SrTiO 3 , mid-infrared drives shown induce a metastable ferroelectric state. Crucial physics is competition between polar instabilities and antiferrodistortive rotations, equilibrium...
Extending the idea of optical microcavities to sound waves, we propose a phonon cavity consisting two semiconductor superlattices enclosing spacer layer. We show that acoustical phonons can be confined in such layered structures when thickness is an integer multiple acoustic half-wavelength at center one superlattice folded minigaps. report Raman scattering experiments that, taking profit microcavity geometry, demonstrate unambiguously observation phonon-cavity vibration...
The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These find temporal overlap pump probe pulses. strong-field dissociation generated quasi-bound dications was establish...
The Linac Coherent Light Source free electron laser is a source of high brightness x rays, 2×1011 photons in ∼5 fs pulse, that can be focused to produce double core vacancies through rapid sequential ionization. This enables vacancy Auger spectroscopy, an entirely new way study femtosecond chemical dynamics with electrons probe the local valence structure molecules near specific atomic core. Using 1.1 keV for x-ray ionization impulsively aligned molecular nitrogen, we observed rich...
Femtosecond midinfrared pulses are used to directly excite the lattice of single-layer manganite La${}_{0.5}$Sr${}_{1.5}$MnO${}_{4}$. Magnetic and orbital orders, as measured by femtosecond resonant soft x-ray diffraction with an free-electron laser, reduced within a few picoseconds. This effect is interpreted displacive exchange quench, prompt shift in equilibrium value magnetic- orbital-order parameters after has been distorted. Control magnetism through ultrafast excitation may be use for...
We report on the ultrafast dynamics of magnetic order in a single crystal CuO at temperature 207 K response to strong optical excitation using femtosecond resonant x-ray diffraction. In experiment, laser pulse induces sudden, nonequilibrium increase disorder. After short delay ranging from 400 fs 2 ps, we observe changes relative intensity ordering diffraction peaks that indicate shift collinear commensurate phase spiral incommensurate phase. These results ultimate speed for this...
Abstract Predicting practical rates of transport in condensed phases enables the rational design materials, devices and processes. This is especially critical to developing low-carbon energy technologies such as rechargeable batteries 1–3 . For ionic conduction, collective mechanisms 4,5 , variation conductivity with timescales 6–8 confinement 9,10 ambiguity phononic origin translation 11,12 call for a direct probe fundamental steps diffusion: ion hops. However, hops are rare-event...
We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From time-dependence Debye-Waller factor, we extract a 4.7 ps time-constant for increase mean-square atomic displacements. The observed diffuse scattering intensity demonstrates that energy transfer from laser-heated electrons phonon modes near X and K points Au fcc Brillouin zone proceeds with timescales 2.3 2.9 ps,...
Abstract The interactions between electrons and lattice vibrations are fundamental to materials behaviour. In the case of group IV–VI, V related materials, these strong, exist near electronic structural phase transitions. prototypical example is PbTe whose incipient ferroelectric behaviour has been recently associated with large phonon anharmonicity thermoelectricity. Here we show that it primarily electron-phonon coupling involving electron states band edges leads instability in PbTe. Using...
Vanadium dioxide, an archetypal correlated-electron material, undergoes insulator-metal transition near room temperature that exhibits electron-correlation-driven and structurally-driven physics. Using ultrafast optical spectroscopy x-ray scattering we show these processes can be disentangled in the time domain. Specifically, following intense sub-picosecond electric-field excitation, a partial collapse of insulating gap occurs within first ps. Subsequently, this electronic reconfiguration...
The recent development of x-ray free electron lasers providing coherent, femtosecond-long pulses high brilliance and variable energy opens new areas scientific research in a variety disciplines such as physics, chemistry, biology. Pump-probe experimental techniques which observe the temporal evolution systems after optical or pulse excitation are one main schemes currently use for ultrafast studies. key challenge these experiments is to reliably achieve spatial overlap pulses. Here we...
We use femtosecond time-resolved hard x-ray scattering to detect coherent acoustic phonons excited during ultrafast laser demagnetization of bcc Fe films. determine the lattice strain propagating through film analysis oscillations in signal as a function momentum transfer. The width wavefront is ~100 fs, similar timescales. First-principles calculations show that high-frequency Fourier components strain, which give rise sharp wavefront, could part originate from non-thermal dynamics not...
We present ultrafast optical pump-probe and x-ray diffraction measurements of the charge density wave dynamics in ${\mathrm{SmTe}}_{3}$ at 300 K. performed Linac Coherent Light Source to directly probe finite-wave-vector order parameter. The reveal coherent oscillations $\ensuremath{\sim}1.6$ THz that become overdamped with increasing fluence. identify this oscillation lattice component amplitude mode. Furthermore, our data allow for a clear identification mode frequency data. In both...
We investigate the order parameter dynamics of stripe-ordered nickelate, La$_{1.75}$Sr$_{0.25}$NiO$_4$, using time-resolved resonant X-ray diffraction. In spite distinct spin and charge energy scales, two parameters' amplitude are found to be linked together due strong coupling. Additionally, vector nature sector introduces a longer re-orientation time scale which is absent in sector. These findings demonstrate that correlation linking symmetry-broken states does not unbind during...