The magnetization measurements on Bi2Sr2CaCu20& single crystals with H parallel to the c axis are presented to show that the critical fluctuations in the magnetization near the H, 2(T) line can be well studied within the two-dimensional nonperturbative scaling theory developed by Tesanovic et al. By using this scaling theory and basic thermodynamic arguments, we obtained the Ginzburg-Landau parameter a (= 115) and dH, 2/dT (= -2.7 T/K) near T, for this material. In addition, we found that these derived parameters are in good agreement with those determined from the study of reversible magnetization in an intermediate field at low temperature.Recently, it has been shown that the critical Auctuations in the thermodynamics of high-T, superconductors near the upper critical-field H, 2(T) line can be studied in terms of the Ginzburg-Landau (GL) field theory on a degenerate manifold spanned by the lowest Landau level (LLL) for Cooper pairs. 'The GL-LLL theory implies that the free energy F (H, T) near the H, 2(T) line is of the form F( T, H) = THf ( At). f ( At) is a scaling function of the variable t =[T -T, (H)]/(TH)", where A is a fieldand temperature-independent coefficient, and n is for a three-dimensional (3D) system, and -, ' for a twodimensional (2D) system. This scaling behavior for some thermodynamic quantities has been observed by several groups for many high-T, superconductors. For instance, a 3D scaling behavior of the magnetization, Ettinghausen effect, and specific heat of the YBa2Cu307 single crystal near the H, 2(T) line was observed by Welp et al. , while a 2D scaling behavior of the magnetization for a c-axisoriented superconductingBi2SrzCa2Cu30, 0 [Bi(2:2:2:3)] thin tape near the H, z(T) line was reported by Li et al.However, there has been no report so far to our knowledge, that demonstrates a clear 2D scaling behavior for the magnetization of superconducting Bi2Sr2CaCu208 [Bi(2:2:1:2)]even though Bi(2:2:1:2) is thought to be a quasi-2D-type superconductor. It is the purpose of this paper to present our magnetization measurements on large Bi(2:2:1:2)single crystals with magnetic field parallel to the c axis, and to show that the critical fluctuations in the magnetization near the H, z( T) line do display a 2D scaling behavior. Furthermore, we shall demonstrate that the magnetization of Bi(2:2:1:2)near the H, 2(T) line can be well studied within the two-dimensional nonper-turbative scaling theory developed by Tesanovic, et al. By using this scaling theory and basic thermodynamic arguments, we obtained the value of the Ginzburg-Landau parameter tc (=115) for superconducting Bi(2:2:1:2),as well as dH, 2/dT (= -2.7 T/K) near T, . These values are found in excellent agreement with those derived by applying the modified Hao-Clem variational model (including the effect of vortex fluctuation in 2D superconductors) to our reversible magnetization data taken in intermediate field at low temperature.Single-crystals Bi(2:2:1:2)were grown by the traveling solvent Qoating zone method.The large crystal used in ou...
