Effects of vortex and anti-vortex excitations in underdoped Bi-2223 bulk single crystals

To gain insights into mechanisms underlying superconducting transition in copper oxide high-transition temperature (T_c) superconductors, we studied transport properties of underdoped Bi_2Sr_2Ca_2Cu_3O_10+δ (Bi-2223) bulk single crystals. The power exponent α (V ∝ I^α) reached 3 just below T_c, and the temperature dependence of in-plane resistivity (ρ_ab) exhibited typical tailing behavior, consistent with Kosterlitz–Thouless transition characteristics. Thus, with increasing temperature, copper oxide high-T_c superconductors undergo transition to the normal state because of destruction of its phase correlations, although a finite Cooper pair density exists at T_c.