361 research outputs found
Domain size effects on the dynamics of a charge density wave in 1T-TaS2
Recent experiments have shown that the high temperature incommensurate (I)
charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower
temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved
x-ray diffraction study of the growth process of the photoinduced I-CDW
domains. The layered nature of the material results in a marked anisotropy in
the size of the photoinduced domains of the I-phase. These are found to grow
self-similarly, their shape remaining unchanged throughout the growth process.
The photoinduced dynamics of the newly formed I-CDW phase was probed at various
stages of the growth process using a double pump scheme, where a first pump
creates I-CDW domains and a second pump excites the newly formed I-CDW state.
We observe larger magnitudes of the coherently excited I-CDW amplitude mode in
smaller domains, which suggests that the incommensurate lattice distortion is
less stable for smaller domain sizes.Comment: 8 pages, 8 figure
The photoinduced transition in magnetoresistive manganites: a comprehensive view
We use femtosecond x-ray diffraction to study the structural response of
charge and orbitally ordered PrCaMnO thin films across a phase
transition induced by 800 nm laser pulses. By investigating the dynamics of
both superlattice reflections and regular Bragg peaks, we disentangle the
different structural contributions and analyze their relevant time-scales. The
dynamics of the structural and charge order response are qualitatively
different when excited above and below a critical fluence . For
excitations below the charge order and the superlattice is only partially
suppressed and the ground state recovers within a few tens of nanosecond via
diffusive cooling. When exciting above the critical fluence the superlattice
vanishes within approximately half a picosecond followed by a change of the
unit cell parameters on a 10 picoseconds time-scale. At this point all memory
from the symmetry breaking is lost and the recovery time increases by many
order of magnitudes due to the first order character of the structural phase
transition
Watching the birth of a charge density wave order: diffraction study on nanometer-and picosecond-scales
Femtosecond time-resolved X-ray diffraction is used to study a photo-induced
phase transition between two charge density wave (CDW) states in 1T-TaS,
namely the nearly commensurate (NC) and the incommensurate (I) CDW states.
Structural modulations associated with the NC-CDW order are found to disappear
within 400 fs. The photo-induced I-CDW phase then develops through a
nucleation/growth process which ends 100 ps after laser excitation. We
demonstrate that the newly formed I-CDW phase is fragmented into several
nanometric domains that are growing through a coarsening process. The
coarsening dynamics is found to follow the universal Lifshitz-Allen-Cahn growth
law, which describes the ordering kinetics in systems exhibiting a
non-conservative order parameter.Comment: 6 pages, 5 figure
Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3
The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by
time resolved x-ray diffraction after photo excitation 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:SrTiO3, we observe a ultrafast relaxation on a
0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be
independent of the initial temperaure 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
Nonantagonistic interactions between the sexes revealed by the ecological consequences of reproductive traits
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73504/1/j.1420-9101.2004.00779.x.pd
Melting of magnetic order in NaOsO<sub>3</sub> by femtosecond laser pulses
NaOsO3 has recently attracted significant attention for the strong coupling between its electronic band structure and magnetic ordering. Here, we used time-resolved magnetic x-ray diffraction to determine the timescale of the photoinduced antiferromagnetic dynamics in NaOsO3. Our measurements are consistent with a sub-100 fs melting of the antiferromagnetic long-range order that occurs significantly faster than the lattice dynamics as monitored by the transient change in intensity of selected Bragg structural reflections, which instead show a decrease of intensity on a timescale of several ps
Peptidyl-Prolyl Isomerase 1 Regulates Ca(2+) Handling by Modulating Sarco(endo)plasmic Reticulum Calcium ATPase and Na(2+)/Ca(2+) Exchanger 1 Protein Levels and Function
BACKGROUND: Aberrant Ca(2+) handling is a prominent feature of heart failure. Elucidation of the molecular mechanisms responsible for aberrant Ca(2+) handling is essential for the development of strategies to blunt pathological changes in calcium dynamics. The peptidyl-prolyl cis-trans isomerase peptidyl-prolyl isomerase 1 (Pin1) is a critical mediator of myocardial hypertrophy development and cardiac progenitor cell cycle. However, the influence of Pin1 on calcium cycling regulation has not been explored. On the basis of these findings, the aim of this study is to define Pin1 as a novel modulator of Ca(2+) handling, with implications for improving myocardial contractility and potential for ameliorating development of heart failure. METHODS AND RESULTS: Pin1 gene deletion or pharmacological inhibition delays cytosolic Ca(2+) decay in isolated cardiomyocytes. Paradoxically, reduced Pin1 activity correlates with increased sarco(endo)plasmic reticulum calcium ATPase (SERCA2a) and Na(2+)/Ca(2+) exchanger 1 protein levels. However, SERCA2a ATPase activity and calcium reuptake were reduced in sarcoplasmic reticulum membranes isolated from Pin1-deficient hearts, suggesting that Pin1 influences SERCA2a function. SERCA2a and Na(2+)/Ca(2+) exchanger 1 associated with Pin1, as revealed by proximity ligation assay in myocardial tissue sections, indicating that regulation of Ca(2+) handling within cardiomyocytes is likely influenced through Pin1 interaction with SERCA2a and Na(2+)/Ca(2+) exchanger 1 proteins. CONCLUSIONS: Pin1 serves as a modulator of SERCA2a and Na(2+)/Ca(2+) exchanger 1 Ca(2+) handling proteins, with loss of function resulting in impaired cardiomyocyte relaxation, setting the stage for subsequent investigations to assess Pin1 dysregulation and modulation in the progression of heart failure
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