Using femtosecond time-resolved x-ray diffraction, we directly monitor the coherent lattice dynamics through an ultrafast charge-density-wave-to-metal transition in the prototypical Peierls system ...K(0.3)MoO(3) over a wide range of relevant excitation fluences. While in the low fluence regime we directly follow the structural dynamics associated with the collective amplitude mode; for fluences above the melting threshold of the electronic density modulation we observe a transient recovery of the periodic lattice distortion. We can describe these structural dynamics as a motion along the coordinate of the Peierls distortion triggered by the prompt collapse of electronic order after photoexcitation. The results indicate that the dynamics of a structural symmetry-breaking transition are determined by a high-symmetry excited state potential energy surface distinct from that of the initial low-temperature state.
Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological ...applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation.
Multiferroics have attracted strong interest for potential applications where electric fields control magnetic order. The ultimate speed of control via magnetoelectric coupling, however, remains ...largely unexplored. Here, we report an experiment in which we drove spin dynamics in multiferroic TbMnO3 with an intense few-cycle terahertz (THz) light pulse tuned to resonance with an electromagnon, an electric-dipole active spin excitation. We observed the resulting spin motion using time-resolved resonant soft x-ray diffraction. Our results show that it is possible to directly manipulate atomic-scale magnetic structures with the electric field of light on a sub-picosecond time scale.
Femtosecond time-resolved x-ray diffraction is employed to study the dynamics of the periodic lattice distortion (PLD) associated with the charge-density wave in K0.3MoO3. Using a multipulse scheme ...we show the ability to extend the lifetime of coherent oscillations of the PLD about the undistorted structure through reexcitation of the electronic states. This suggests that it is possible to enter a regime where the symmetry of the potential energy landscape corresponds to the high-symmetry phase but the scattering pathways that lead to the damping of coherent dynamics are still controllable by altering the electronic state population. The demonstrated control over the coherence time offers different routes for the manipulation of coherent lattice states.
We photoexcite SrTiO
3
and EuTiO
3
in their purely soft-mode-driven structurally distorted phase and trace the structural order parameter via ultra-short x-rays. We observe a rapid decay for SrTiO
3
...and an intriguing transient enhancement for EuTiO3.
We report on the ultrafast dynamics of charge order and structural response during the photoinduced suppression of charge and orbital order in a mixed-valence manganite. Employing femtosecond ...time-resolved resonant x-ray diffraction below and at the Mn K absorption edge, we present a method to disentangle the transient charge order and structural dynamics in thin films of Pr0.5Ca0.5MnO3. Based on the static resonant scattering spectra, we extract the dispersion correction of charge-ordered Mn3+ and Mn4+ ions, allowing us to separate the transient contributions of purely charge order from structural contributions to the scattering amplitude after optical excitation. Our finding of a coherent structural mode at around 2.3THz, which primarily modulates the lattice but does not strongly affect the charge order, supports the picture of the charge order being the driving force of the combined charge, orbital, and structural transition.
The ultrafast dynamics of the octahedral rotation in Ca : SrTi O3 is studied by time-resolved x-ray diffraction after photoexcitation over the band gap. By monitoring the diffraction intensity of a ...superlattice reflection that is directly related to the structural order parameter of the soft-mode driven antiferrodistortive phase in Ca : SrTi O3 , we observe an ultrafast relaxation on a 0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be independent of the initial temperature despite large changes in the corresponding soft-mode frequency. A further, much smaller reduction on a slower picosecond timescale is attributed to thermal effects. Time-dependent density-functional-theory calculations show that the fast response can be ascribed to an ultrafast displacive modification of the soft-mode potential towards the normal state induced by holes created in the oxygen 2p states.
To determine the effects of aspirin and ibuprofen on the pharmacokinetics and pharmacodynamics of glyburide in healthy volunteers.
Single-center, randomized, two-way, crossover design following an ...initial baseline evaluation phase.
Outpatient, university-based ambulatory care facility.
Sixteen healthy nonsmoking men aged 20-34 years.
Three phases consisting of six treatments. Phase 1 began with treatment A, a baseline oral glucose tolerance test (GTT), followed by treatment B, glyburide 5 mg plus a GTT. The other two phases were administered in a crossover design. Phase 2 consisted of the administration of aspirin 975 mg qid for 4 days. On day 3 a GTT was administered (treatment C) and on day 4 glyburide 5 mg plus a GTT was administered (treatment E). Phase 3 consisted of the administration of ibuprofen 600 mg qid for 4 days with a GTT on day 3 (treatment D) and glyburide 5 mg plus a GTT on day 4 (treatment F).
Serum glyburide concentrations after each treatment, as well as glucose and insulin, ibuprofen, and salicylate serum concentrations and glyburide free fractions.
Aspirin administration resulted in an 85% increase in mean total glyburide oral clearance and a 29% increase in glyburide free fraction. Ibuprofen administration resulted in a slight increase in mean glyburide free fraction, but no significant changes in glyburide pharmacokinetic parameters were observed. Insulin concentrations were increased during the glyburide plus aspirin treatment. Conflicting results were observed in the glucose parameters.
The potential for this glyburide-aspirin interaction resulting in a transient hypoglycemia should be considered in diabetic patients receiving glyburide therapy.
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