1,571 research outputs found
Ergodicity and Mixing in Quantum Dynamics
After a brief historical review of ergodicity and mixing in dynamics,
particularly in quantum dynamics, we introduce definitions of quantum
ergodicity and mixing using the structure of the system's energy levels and
spacings. Our definitions are consistent with usual understanding of ergodicity
and mixing. Two parameters concerning the degeneracy in energy levels and
spacings are introduced. They are computed for right triangular billiards and
the results indicate a very close relation between quantum ergodicity (mixing)
and quantum chaos. At the end, we argue that, besides ergodicity and mixing,
there may exist a third class of quantum dynamics which is characterized by a
maximized entropy.Comment: 10 pages, 6 figures and 1 tabl
The effect of Cr impurity to superconductivity in electron-doped BaFe2-xNixAs2
We use transport and magnetization measurements to study the effect of
Cr-doping to the phase diagram of the electron-doped superconducting
BaFe2-xNixAs2 iron pnictides. In principle, adding Cr to electron-doped
BaFe2-xNixAs2 should be equivalent to the effect of hole-doping. However, we
find that Cr doping suppresses superconductivity via impurity effect, while not
affecting the normal state resistivity above 100 K. We establish the phase
diagram of Cr-doped BaFe2-x-yNixCryAs2 iron pnictides, and demonstrate that
Cr-doping near optimal superconductivity restore the long-range
antiferromagnetic order suppressed by superconductivity.Comment: 10 pages, 5 figure
Development of Powder-in-Tube Processed Iron Pnictide Wires and Tapes
The development of the PIT fabrication process of iron pnictide
superconducting wires and tapes has been carried out in order to enhance their
transport properties. Silver was found to be the best sheath material, since no
reaction layer was observed between the silver sheath and the superconducting
core. The grain connectivity of iron pnictide wires and tapes has been markedly
improved by employing Ag or Pb as dopants. At present, critical current
densities in excess of 3750 A/cm^2 (Ic = 37.5 A) at 4.2 K have been achieved on
Ag-sheathed SrKFeAs wires prepared with the above techniques, which is the
highest in iron-based wires and tapes so far. Moreover, Ag-sheathed Sm-1111
superconducting tapes were successfully prepared by PIT method at temperatures
as low as 900C, instead of commonly used temperatures of 1200C. These results
demonstrate the feasibility of producing superconducting pnictide composite
wires, even grain boundary properties require much more attention.Comment: 4 pages, 6 figures. Submitted to ASC2010 proceeding
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