1,628 research outputs found
First-Order Type Effects in YBaCuO at the Onset of Superconductivity
We present results of Raman scattering experiments on tetragonal for doping levels between 0 and
0.07 holes/CuO. Below the onset of superconductivity at , we find evidence of a diagonal superstructure. At ,
lattice and electron dynamics change discontinuously with the charge and spin
properties being renormalized at all energy scales. The results indicate that
charge ordering is intimately related to the transition at and
that the maximal transition temperature to superconductivity at optimal doping
depends on the type of ordering at .Comment: 4 pages, 4 figure
Observation of out-of-phase bilayer plasmons in YBa_2Cu_3O_7-delta
The temperature dependence of the c-axis optical conductivity \sigma(\omega)
of optimally and overdoped YBa_2Cu_3O_x (x=6.93 and 7) is reported in the far-
(FIR) and mid-infrared (MIR) range. Below T_c we observe a transfer of spectral
weight from the FIR not only to the condensate at \omega = 0, but also to a new
peak in the MIR. This peak is naturally explained as a transverse out-of-phase
bilayer plasmon by a model for \sigma(\omega) which takes the layered crystal
structure into account. With decreasing doping the plasmon shifts to lower
frequencies and can be identified with the surprising and so far not understood
FIR feature reported in underdoped bilayer cuprates.Comment: 7 pages, 3 eps figures, Revtex, epsfi
Electron interactions and charge ordering in LaSrCuO
We present results of inelastic light scattering experiments on
single-crystalline LaSrCuO in the doping range and TlBaCuO at and . The main
emphasis is placed on the response of electronic excitations in the
antiferromagnetic phase, in the pseudogap range, in the superconducting state,
and in the essentially normal metallic state at , where no
superconductivity could be observed. In most of the cases we compare B
and B spectra which project out electronic properties close to
and , respectively. In the channel of electron-hole excitations
we find universal behavior in B symmetry as long as the material
exhibits superconductivity at low temperature. In contrast, there is a strong
doping dependence in B symmetry: (i) In the doping range we observe rapid changes of shape and temperature dependence of the
spectra. (ii) In LaSrCuO new structures appear for
which are superposed on the electron-hole continuum. The temperature dependence
as well as model calculations support an interpretation in terms of
charge-ordering fluctuations. For the response from fluctuations
disappears at B and appears at B symmetry in full agreement with
the orientation change of stripes found by neutron scattering. While, with a
grain of salt, the particle-hole continuum is universal for all cuprates the
response from fluctuating charge order in the range is so
far found only in LaSrCuO. We conclude that
LaSrCuO is close to static charge order and, for this reason,
may have a suppressed .Comment: 17 pages, 15 figure
Magnetic Breakdown in the electron-doped cuprate superconductor NdCeCuO: the reconstructed Fermi surface survives in the strongly overdoped regime
We report on semiclassical angle-dependent magnetoresistance oscillations
(AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate
superconductor NdCeCuO. Our data provide convincing evidence
for magnetic breakdown in the system. This shows that a reconstructed
multiply-connected Fermi surface persists, at least at strong magnetic fields,
up to the highest doping level of the superconducting regime. Our results
suggest an intimate relation between translational symmetry breaking and the
superconducting pairing in the electron-doped cuprate superconductors.Comment: 5 pages, 4 figures, submitted to PR
Urban transportation: Perspectives on mobility and choice
A study of urban transportation systems are presented characterized by intensive scrutiny of many ideas, philosophies, and academic perspectives. This report is intended to communicate some dimensions of the urban transportation problem to the general public
Hole depletion and localization due to disorder in insulating PrBa2Cu3O7-d: a Compton scattering study
The (mostly) insulating behaviour of PrBa2Cu3O7-d is still unexplained and
even more interesting since the occasional appearance of superconductivity in
this material. Since YBa2Cu3O7-d is nominally iso-structural and always
superconducting, we have measured the electron momentum density in these
materials. We find that they differ in a striking way, the wavefunction
coherence length in PrBa2Cu3O7-d being strongly suppressed. We conclude that Pr
on Ba-site substitution disorder is responsible for the metal-insulator
transition. Preliminary efforts at growth with a method to prevent disorder
yield 90K superconducting PrBa2Cu3O7-d crystallites.Comment: 4 pages, 3 figures, revised version submitted to PR
Correlation between Fermi surface transformations and superconductivity in the electron-doped high- superconductor NdCeCuO
Two critical points have been revealed in the normal-state phase diagram of
the electron-doped cuprate superconductor NdCeCuO by exploring
the Fermi surface properties of high quality single crystals by high-field
magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas
effect shows that the weak superlattice potential responsible for the Fermi
surface reconstruction in the overdoped regime extrapolates to zero at the
doping level corresponding to the onset of superconductivity.
Second, the high-field Hall coefficient exhibits a sharp drop right below
optimal doping where the superconducting transition
temperature is maximum. This drop is most likely caused by the onset of
long-range antiferromagnetic ordering. Thus, the superconducting dome appears
to be pinned by two critical points to the normal state phase diagram.Comment: 9 pages; 7 figures; 1 tabl
Fermi surface and order parameter driven vortex lattice structure transitions in twin-free YBa2Cu3O7
We report on small-angle neutron scattering studies of the intrinsic vortex
lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8
T. Because of the suppressed pinning to twin-domain boundaries, a new distorted
hexagonal VL structure phase is stabilized at intermediate fields. It is
separated from a low-field hexagonal phase of different orientation and
distortion by a first-order transition at 2.0(2) T that is probably driven by
Fermi surface effects. We argue that another first-order transition at 6.7(2)
T, into a rhombic structure with a distortion of opposite sign, marks a
crossover from a regime where Fermi surface anisotropy is dominant, to one
where the VL structure and distortion is controlled by the order-parameter
anisotropy.Comment: 4 pages, 3 figures (2 color), minor change
Microbial Biofilm Community Variation in Flowing Habitats: Potential Utility as Bioindicators of Postmortem Submersion Intervals
Biofilms are a ubiquitous formation of microbial communities found on surfaces in aqueous environments. These structures have been investigated as biomonitoring indicators for stream heath, and here were used for the potential use in forensic sciences. Biofilm successional development has been proposed as a method to determine the postmortem submersion interval (PMSI) of remains because there are no standard methods for estimating the PMSI and biofilms are ubiquitous in aquatic habitats. We sought to compare the development of epinecrotic (biofilms on Sus scrofa domesticus carcasses) and epilithic (biofilms on unglazed ceramic tiles) communities in two small streams using bacterial automated ribosomal intergenic spacer analysis. Epinecrotic communities were significantly different from epilithic communities even though environmental factors associated with each stream location also had a significant influence on biofilm structure. All communities at both locations exhibited significant succession suggesting that changing communities throughout time is a general characteristic of stream biofilm communities. The implications resulting from this work are that epinecrotic communities have distinctive shifts at the first and second weeks, and therefore the potential to be used in forensic applications by associating successional changes with submersion time to estimate a PMSI. The influence of environmental factors, however, indicates the lack of a successional pattern with the same organisms and a focus on functional diversity may be more applicable in a forensic context
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