4,465 research outputs found
Flux pinning and phase separation in oxygen rich La2-xSrxCuO4+y system
We have studied the magnetic characteristics of a series of super-oxygenated
La2-xSrxCuO4+y samples. As shown in previous work, these samples spontaneously
phase separate into an oxygen rich superconducting phase with a TC near 40 K
and an oxygen poor magnetic phase that also orders near 40 K. All samples
studied are highly magnetically reversible even to low temperatures. Although
the internal magnetic regions of these samples might be expected to act as
pinning sites, our present study shows that they do not favor flux pinning.
Flux pinning requires a matching condition between the defect and the
superconducting coherence length. Thus, our results imply that the magnetic
regions are too large to act as pinning centers. This also implies that the
much greater flux pinning in typical La2-xSrxCuO4 materials is the result of
nanoscale inhomogeneities that grow to become the large magnetic regions in the
super-oxygenated materials. The superconducting regions of the phase separated
materials are in that sense cleaner and more homogenous than in the typical
cuprate superconductor.Comment: 4 figures 8 pages Submitted to PR
Limits on Phase Separation for Two-Dimensional Strongly Correlated Electrons
From calculations of the high temperature series for the free energy of the
two-dimensional t-J model we construct series for ratios of the free energy per
hole. The ratios can be extrapolated very accurately to low temperatures and
used to investigate phase separation. Our results confirm that phase separation
occurs only for J/t greater than 1.2. Also, the phase transition into the phase
separated state has Tc of approximately 0.25J for large J/t.Comment: 4 pages, 6 figure
On the Relationship Between the Pseudo- and Superconducting Gaps: Effects of Residual Pairing Correlations Below Tc
The existence of a normal state spectral gap in underdoped cuprates raises
important questions about the associated superconducting phase. For example,
how does this pseudogap evolve into its below Tc counterpart? In this paper we
characterize this unusual superconductor by investigating the nature of the
``residual'' pseudogap below Tc and, find that it leads to an important
distinction between the superconducting excitation gap and order parameter. Our
approach is based on a conserving diagrammatic BCS Bose-Einstein crossover
theory which yields the precise BCS result in weak coupling at any T<Tc and
reproduces Leggett's results in the T=0 limit. We explore the resulting
experimental implications.Comment: REVTeX, 4 pages, 1 EPS figure (included
Luther-Emery Stripes, RVB Spin Liquid Background and High Tc Superconductivity
The stripe phase in high Tc cuprates is modeled as a single stripe coupled to
the RVB spin liquid background by the single particle hopping process. In
normal state, the strong pairing correlation inherent in RVB state is thus
transfered into the Luttinger stripe and drives it toward spin-gap formation
described by Luther-Emery Model. The establishment of global phase coherence in
superconducting state contributes to a more relevant coupling to
Luther-Emery Stripe and leads to gap opening in both spin and charge sectors.
Physical consequences of the present picture are discussed, and emphasis is put
on the unification of different energy scales relevant to cuprates, and good
agreement is found with the available experimental results, especially in
ARPES.Comment: 4 pages, RevTe
Impact Of Two-Stage Weaning On Calf Growth, Behavior, and Vocalizations
https://scholarworks.moreheadstate.edu/student_scholarship_posters/1174/thumbnail.jp
Probing Pseudogap by Josephson Tunneling
We propose here an experiment aimed to determine whether there are
superconducting pairing fluctuations in the pseudogap regime of the high-
materials. In the experimental setup, two samples above are brought into
contact at a single point and the differential AC conductivity in the presence
of a constant applied bias voltage between the samples, , should be
measured. We argue the the pairing fluctuations will produce randomly
fluctuating Josephson current with zero mean, however the current-current
correlator will have a characteristic frequency given by Josephson frequency
. We predict that the differential AC conductivity
should have a peak at the Josephson frequency with the width determined by the
phase fluctuations time.Comment: 4 pages, 2 eps figure
A Vector Supersymmetry in Noncommutative U(1) Gauge Theory with the Slavnov Term
We consider noncommutative U(1) gauge theory with the additional term,
involving a scalar field lambda, introduced by Slavnov in order to cure the
infrared problem. we show that this theory, with an appropriate space-like
axial gauge-fixing, wxhibits a linear vector supersymmetry similar to the one
present in the 2-dimensional BF model. This vector supersymmetry implies that
all loop corrections are independent of the -vertex and thereby
explains why Slavnov found a finite model for the same gauge-fixing.Comment: 18 pages, 3 figures; v2 Acknowledgments adde
Low Gravity Guidance System for Airborne Microgravity Research
Microgravity research techniques have been established to achieve a greater understanding of the role of gravity in the fundamentals of a variety of physical phenomena and material processing. One technique in use at the NASA Lewis Research Center involves flying Keplarian trajectories with a modified Lear Jet and DC-9 aircraft to achieve a highly accurate Microgravity environment by neutralizing accelerations in all three axis of the aircraft. The Low Gravity Guidance System (LGGS) assists the pilot and copilot in flying the trajectories by displaying the aircraft acceleration data in a graphical display format. The Low Gravity Guidance System is a microprocessor based system that acquires and displays the aircraft acceleration information. This information is presented using an electroluminescent display mounted over the pilot's instrument panel. The pilot can select the Microgravity range that is required for a given research event. This paper describes the characteristics, design, calibration and testing of the Low Gravity Guidance System Phase 3, significant lessons from earlier systems and the developmental work on future systems
Similarity of slow stripe fluctations between Sr-doped cuprates and oxygen-doped nickelates
Stripe fluctuations in La2NiO4.17 have been studied by 139La NMR using the
field and temperature dependence of the linewidth and relaxation rates. In the
formation process of the stripes the NMR line intensity is maximal below 230K,
starts to diminish around 140K, disappears around 50K and recovers at 4K. These
results are shown to be consistent with, but completely complementary to
neutron measurements, and to be generic for oxygen doped nickelates and
underdoped cuprates.Comment: 4 pages including 4 figure
Antiferromagnetic spin ladders effectively coupled by one-dimensional electron liquids
We study a model of the stripe state in strongly correlated systems
consisting of an array of antiferromagnetic spin ladders, each with
legs, coupled to each other through the spin-exchange interaction to charged
stripes in between each pair of ladders. The charged stripes are assumed to be
Luttinger liquids in a spin-gap regime (Luther-Emery). An effective interaction
for a pair of neighboring ladders is calculated by integrating out the gapped
spin degree of freedom in the charged stripe. The low energy effective theory
of each ladder is the usual nonlinear -model with additional cross
couplings of neighboring ladders. These interactions are found to favor either
in-phase or anti-phase short range spin orderings depending on whether the
charge stripe is site-centered or bond-centered as well as on its filling
factor and other physical parameters of the charged stripe.Comment: 4 pages with 1 figure, revised introduction and discussion section
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