1,859 research outputs found
Dynamical decoherence of the light induced interlayer coupling in YBaCuO
Optical excitation of apical oxygen vibrations in
YBaCuO has been shown to enhance its c-axis
superconducting-phase rigidity, as evidenced by a transient blue shift of the
equilibrium inter-bilayer Josephson plasma resonance. Surprisingly, a transient
c-axis plasma mode could also be induced above T by the same apical
oxygen excitation, suggesting light activated superfluid tunneling throughout
the pseudogap phase of YBaCuO. However, despite the
similarities between the above T transient plasma mode and the
equilibrium Josephson plasmon, alternative explanations involving high mobility
quasiparticle transport should be considered. Here, we report an extensive
study of the relaxation of the light-induced plasmon into the equilibrium
incoherent phase. These new experiments allow for a critical assessment of the
nature of this mode. We determine that the transient plasma relaxes through a
collapse of its coherence length rather than its carrier (or superfluid)
density. These observations are not easily reconciled with quasiparticle
interlayer transport, and rather support transient superfluid tunneling as the
origin of the light-induced interlayer coupling in
YBaCuO.Comment: 27 pages (17 pages main text, 10 pages supplementary), 5 figures
(main text
The Animal Research Controversy: Protest, Process & Public Policy
The controversy today regarding the use of animals in research appears on the surface to be a strongly polarized struggle between the scientific community and the animal protection movement. However, there is a wide range of opinions and philosophies on both sides. Mistrust between the factions has blossomed while communication has withered. Through the 1960s, 1970s and early 1980s, the animal movement grew in numbers and financial resources, and developed much greater public recognition and political clout. The research community paid relatively little attention to the animal movement for much of this period but, alarmed by several public relations coups in the 1980s, it has become more vociferous and has shifted from a reactive defense to a proactive, aggressive offense.https://www.wellbeingintlstudiesrepository.org/ebooks/1001/thumbnail.jp
The Animal Research Controversy: Protest, Process & Public Policy
The controversy today regarding the use of animals in research appears on the surface to be a strongly polarized struggle between the scientific community and the animal protection movement. However, there is a wide range of opinions and philosophies on both sides. Mistrust between the factions has blossomed while communication has withered. Through the 1960s, 1970s and early 1980s, the animal movement grew in numbers and financial resources, and developed much greater public recognition and political clout. The research community paid relatively little attention to the animal movement for much of this period but, alarmed by several public relations coups in the 1980s, it has become more vociferous and has shifted from a reactive defense to a proactive, aggressive offense
Real-time optical manipulation of cardiac conduction in intact hearts
Optogenetics has provided new insights in cardiovascular research, leading to new methods for cardiac pacing, resynchronization therapy and cardioversion. Although these interventions have clearly demonstrated the feasibility of cardiac manipulation, current optical stimulation strategies do not take into account cardiac wave dynamics in real time. Here, we developed an all‐optical platform complemented by integrated, newly developed software to monitor and control electrical activity in intact mouse hearts. The system combined a wide‐field mesoscope with a digital projector for optogenetic activation. Cardiac functionality could be manipulated either in free‐run mode with submillisecond temporal resolution or in a closed‐loop fashion: a tailored hardware and software platform allowed real‐time intervention capable of reacting within 2 ms. The methodology was applied to restore normal electrical activity after atrioventricular block, by triggering the ventricle in response to optically mapped atrial activity with appropriate timing. Real‐time intraventricular manipulation of the propagating electrical wavefront was also demonstrated, opening the prospect for real‐time resynchronization therapy and cardiac defibrillation. Furthermore, the closed‐loop approach was applied to simulate a re‐entrant circuit across the ventricle demonstrating the capability of our system to manipulate heart conduction with high versatility even in arrhythmogenic conditions. The development of this innovative optical methodology provides the first proof‐of‐concept that a real‐time optically based stimulation can control cardiac rhythm in normal and abnormal conditions, promising a new approach for the investigation of the (patho)physiology of the heart
High magnetic field studies of the Vortex Lattice structure in YBa2Cu3O7
We report on small angle neutron scattering measurements of the vortex
lattice in twin-free YBa2Cu3O7, extending the previously investigated maximum
field of 11~T up to 16.7~T with the field applied parallel to the c axis. This
is the first microscopic study of vortex matter in this region of the
superconducting phase. We find the high field VL displays a rhombic structure,
with a field-dependent coordination that passes through a square configuration,
and which does not lock-in to a field-independent structure. The VL pinning
reduces with increasing temperature, but is seen to affect the VL correlation
length even above the irreversibility temperature of the lattice structure. At
high field and temperature we observe a melting transition, which appears to be
first order, with no detectable signal from a vortex liquid above the
transition
Doping-Dependent Raman Resonance in the Model High-Temperature Superconductor HgBa2CuO4+d
We study the model high-temperature superconductor HgBa2CuO4+d with
electronic Raman scattering and optical ellipsometry over a wide doping range.
The resonant Raman condition which enhances the scattering cross section of
"two-magnon" excitations is found to change strongly with doping, and it
corresponds to a rearrangement of inter-band optical transitions in the 1-3 eV
range seen by ellipsometry. This unexpected change of the resonance condition
allows us to reconcile the apparent discrepancy between Raman and x-ray
detection of magnetic fluctuations in superconducting cuprates. Intriguingly,
the strongest variation occurs across the doping level where the antinodal
superconducting gap reaches its maximum.Comment: 4 pages, 4 figures, contact authors for Supplemental Materia
Momentum-dependent charge correlations in YBaCuO superconductors probed by resonant x-ray scattering: Evidence for three competing phases
We have used resonant x-ray scattering to determine the momentum dependent
charge correlations in YBaCuO samples with highly ordered
chain arrays of oxygen acceptors (ortho-II structure). The results reveal
nearly critical, biaxial charge density wave (CDW) correlations at in-plane
wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity
exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length
are enhanced as superconductivity is weakened by an external magnetic field.
Analogous experiments were carried out on a YBaCuO crystal with
a dilute concentration of spinless (Zn) impurities, which had earlier been
shown to nucleate incommensurate magnetic order. Compared to pristine crystals
with the same doping level, the CDW amplitude and correlation length were found
to be strongly reduced. These results indicate a three-phase competition
between spin-modulated, charge-modulated, and superconducting states in
underdoped YBaCuO.Comment: 6 pages, 3 figures revised version, to appear in Phys. Rev. Let
Similar zone-center gaps in the low-energy spin-wave spectra of NaFeAs and BaFe2As2
We report results of inelastic-neutron-scattering measurements of low-energy
spin-wave excitations in two structurally distinct families of iron-pnictide
parent compounds: Na(1-{\delta})FeAs and BaFe2As2. Despite their very different
values of the ordered magnetic moment and N\'eel temperatures, T_N, in the
antiferromagnetic state both compounds exhibit similar spin gaps of the order
of 10 meV at the magnetic Brillouin-zone center. The gap opens sharply below
T_N, with no signatures of a precursor gap at temperatures between the
orthorhombic and magnetic phase transitions in Na(1-{\delta})FeAs. We also find
a relatively weak dispersion of the spin-wave gap in BaFe2As2 along the
out-of-plane momentum component, q_z. At the magnetic zone boundary (q_z = 0),
spin excitations in the ordered state persist down to 20 meV, which implies a
much smaller value of the effective out-of-plane exchange interaction, J_c, as
compared to previous estimates based on fitting the high-energy spin-wave
dispersion to a Heisenberg-type model.Comment: 5 pages, 4 figures, 1 tabl
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