Scaling behavior and 3D-2D dimensional crossover in ceramic Tl 2Ba 2Ca 2Cu 3O 10−δ high- Tc superconductors

Abstract

The scalng behavior and dimensional crossover in ceramic Tl 2Ba 2Ca 2Cu 3O 10−δ high- T c superconductors in magnetic fields 0 ≤ H ≤ 12000 Oe are determined by means of comprehensive studies of I– V curve characteristics. In the low magnetic field region 0 ≤ H ≤ 2000 Oe, well-defined three-dimensional (3D) vortex-glass phase transition temperatures T g( H) are found. All of the nonlinear I– V curves above and below T g( H) can be collapsed into two universal lines with the dynamic and static critical exponents z = 2.4 ± 0.6, v = 1.0 ± 0.2, clearly showing that the system is in 3D. When H ≈ 2000 Oe and above, the I– V curves on the log-log scale plot begin to be tortuous and this indicates that the system deviates from the 3D behavior. When H ≥ 6000 Oe, all of the I– V curves can be collapsed into one universal line with critical exponents p = 2.3 ± 0.2 and v 2d = 2.0 ± 0.3, which stands for a two dimensional (2D) vortex-glass scaling phenomenon. Our data show that in the quasi-2D region the characteristic temperature T 0( H) continuously decreases as the magnetic field increases. By extensions of 3D vortex-glass phase transition model and quasi-2D scaling process into the intermediate field region (2000 < H < 6000 Oe), we find a correlation between T 0( H) and T g( H). Combining results obtained from the three different regions, a complete phase transition line is determined in the whole field region 0 ≤ H ≤ 12000 Oe.