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Abstract:
A number of underdoped Bi2Sr2CaCu2Oy single crystals have been obtained
by two different ways: (1) substitution of Y for Ca, and (2) removing
oxygen from crystals by vacuum annealing. The in-plane resistivity
(rho(ab)) measurements reveal different transport properties between
these crystals. For the Y-doped crystals, rho(ab)(T) exhibits metallic
behavior until the crystal reaches a doping level where the
metal-insulator transition should occur. An S-like T-dependent
rho(ab)(T) in the underdoped samples, similar to the observations in
underdoped YBa2Cu3O7-y and La2-xSrxCuO4, was observed. However, for
vacuum-annealed crystals, rho(ab)(T) becomes nonmetallic. We analyze the
data and argue that the disorder introduced by vacuum annealing is much
greater than that by Y doping as long as the crystals have the same T-c.
