T. Noji et al., CARRIER DEPENDENCES OF ANISOTROPY AND IRREVERSIBILITY FIELD IN PB2SR2Y1-XCAXCU3O8 SINGLE-CRYSTALS, Physica. C, Superconductivity, 255(1-2), 1995, pp. 10-18
Anisotropic properties of the electrical resistivity and the resistive
superconducting transition under magnetic fields have been investigat
ed for the single-crystal Pb2Sr2Y1-xCaxCuxO8 with 0 less than or equal
to x less than or equal to 0.5 in the so-called underdoped region. Th
e anisotropic parameter gamma = (m(c)/m(ab)*)(1/2) is found to increa
se from similar to 5 to similar to 24 with decreasing x, namely, with
decreasing hole concentration. The irreversibility field H-irr has bee
n studied from the magnetization measurements for H parallel to c-axis
. In the high-temperature regime near T-c, H-irr is found to be propor
tional to (1 - T/T-c)(3/2) for x similar to 0.5 and to (1 - T/T-c)(3/2
) or (1 - T/T-c)(2) for smaller x values. In this regime, H-irr is als
o found to be proportional to gamma(-2). In the low-temperature regime
, on the other hand, H-irr grows exponentially as approximately expres
sed as e(-T/To) and shows a still stronger growth as e(To/T) at much l
ower temperatures for smaller x values. These behaviors are discussed
in terms of flux creep, vortex-lattice melting and vortex-glass meltin
g.