153,703 research outputs found
Theory of point contact spectroscopy in electron-doped cuprates
In the hole-doped -wave cuprate superconductor, due to the
midgap surface state (MSS), a zero bias conductance peak (ZBCP) is widely
observed in [110] interface point contact spectroscopy (PCS). However, ZBCP of
this geometry is rarely observed in the electron-doped cuprates, even though
their pairing symmetry is still likely the -wave. We argue
that this is due to the coexistence of antiferromagnetic (AF) and the
superconducting (SC) orders. Generalizing the Blonder-Tinkham-Klapwijk (BTK)
formula to include an AF coupling, it is shown explicitly that the MSS is
destroyed by the AF order. The calculated PCS is in good agreement with the
experiments.Comment: 5 pages, 2 figures. Replaced with published versio
Model checking probabilistic and stochastic extensions of the pi-calculus
We present an implementation of model checking for probabilistic and stochastic extensions of the pi-calculus, a process algebra which supports modelling of concurrency and mobility. Formal verification techniques for such extensions have clear applications in several domains, including mobile ad-hoc network protocols, probabilistic security protocols and biological pathways. Despite this, no implementation of automated verification exists. Building upon the pi-calculus model checker MMC, we first show an automated procedure for constructing the underlying semantic model of a probabilistic or stochastic pi-calculus process. This can then be verified using existing probabilistic model checkers such as PRISM. Secondly, we demonstrate how for processes of a specific structure a more efficient, compositional approach is applicable, which uses our extension of MMC on each parallel component of the system and then translates the results into a high-level modular description for the PRISM tool. The feasibility of our techniques is demonstrated through a number of case studies from the pi-calculus literature
A new numerical approach for compressible viscous flows
A numerical approach for computing unsteady compressible viscous flows was developed. This approach offers the capability of confining the region of computation to the viscous region of the flow. The viscous region is defined as the region where the vorticity is nonnegligible and the difference in dilatation between the potential flow and the real flow around the same geometry is also nonnegligible. The method was developed and tested. Also, an application of the procedure to the solution of the steady Navier-Stokes equations for incompressible internal flows is presented
Surface Contribution to Raman Scattering from Layered Superconductors
Generalizing recent work, the Raman scattering intensity from a semi-infinite
superconducting superlattice is calculated taking into account the surface
contribution to the density response functions. Our work makes use of the
formalism of Jain and Allen developed for normal superlattices. The surface
contributions are shown to strongly modify the bulk contribution to the
Raman-spectrum line shape below , and also may give rise to additional
surface plasmon modes above . The interplay between the bulk and
surface contribution is strongly dependent on the momentum transfer
parallel to layers. However, we argue that the scattering
cross-section for the out-of-phase phase modes (which arise from interlayer
Cooper pair tunneling) will not be affected and thus should be the only
structure exhibited in the Raman spectrum below for relatively large
. The intensity is small but perhaps observable.Comment: 14 pages, RevTex, 6 figure
Giant isotope effect and spin state transition induced by oxygen isotope exchange in (
We systematically investigate effect of oxygen isotope in
which shows a crossover with x from
ferromagnetic metal to the insulator with spin-state transition. A striking
feature is that effect of oxygen isotope on the ferromagnetic transition is
negligible in the metallic phase, while replacing with leads
to a giant up-shift of the spin-state transition temperature () in the
insulating phase, especially shifts from 36 to 54 K with isotope
component for the sample with x=0.175. A metal-insulator
transition is induced by oxygen isotope exchange in the sample x=0.172 being
close to the insulating phase. The contrasting behaviors observed in the two
phases can be well explained by occurrence of static Jahn-Teller distortions in
the insulating phase, while absence of them in the metallic phase.Comment: 4 pages, 5 figure
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