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要旨:
We report measurements of the magnetic-field dependence of the resistive
transition in Tl2Ba2CuO6+delta for several crystals with transition
temperatures in the range 15 K less-than-or-equal-to T(c)
less-than-or-equal-to 62 K. The transition of the most overdoped sample
(with the lowest transition temperature) shifts monotonically to lower
temperature with increasing field with no appreciable change in shape.
As reported previously [A. P. Mackenzie et al., Phys. Rev. Lett. 71,
1238 (1993)], the behavior of the upper critcal field (H(c2)) inferred
from these measurements does not, however, have the classical BCS form.
The samples with higher transition temperatures show a gradual and
systematic crossover to field-broadened transitions, with a kneelike
structure developing in sufficiently high fields. Some possible
interpretations of these observations are discussed.
