44 research outputs found
Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single Crystals
Optimally-doped La1.85Sr0.15CuO4 single crystals have been investigated by dc
and ac magnetic measurements. These crystals have rectangular needle-like
shapes with the long needle axis parallel to the crystallographic c axis
(c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the
temperature dependence of the upper critical fields (HC2) and the surface
critical field (HC3) were measured. The H-T phase diagram is presented. Close
to TC =35 K, for the c-crystal, {\gamma}c = / = 1.80(2), whereas for the
a-crystal the {\gamma}a = / =4.0(2) obtained, is much higher than the
theoretical value 1.69. At low applied dc fields, positive field-cooled
branches known as the "paramagnetic Meissner effect" (PME) are observed, their
magnitude is inversely proportional to H. The anisotropic PME is observed in
both a- and c-crystals, only when the applied field is along the basal planes.
It is speculated that the high {\gamma}a and the PME are connected to each
other.Comment: 10 pages, 7 figuer
Parametric Amplification of Nonlinear Response of Single Crystal Niobium
Giant enhancement of the nonlinear response of a single crystal Nb sample,
placed in {\it a pumping ac magnetic field}, has been observed experimentally.
The experimentally observed amplitude of the output signal is about three
orders of magnitude higher than that seen without parametric pumping. The
theoretical analysis based on the extended double well potential model provides
a qualitative explanation of the experimental results as well as new
predictions of two bifurcations for specific values of the pumping signal.Comment: 6 pages, 10 figure