Myoung-Kwang Bae

Synthesis and superconducting properties of HgBa2Ca2Cu3O8 +x

The influence of precursor composition, nominal mercury vapour pressure (PHg) and reaction temperature (t) on the formation of HgBa2Ca2Cu3O8 +x have been studied. By reducing the empty space inside the quartz tube, we could increase PHg higher than 200 atm and obtain samples containing only HgBa2Ca2Cu3O8 +x as the superconducting phase, with Tc(onset)= 134 K and Tc(zero)= 131 K.

Conductivity fluctuation in HBCCO superconductor

Abstract We have analyzed the measured excess conductivity of a HBCCO high- T c superconductor as a function of temperature, which is attributed to the fluctuation of superconducting order parameter above T c 0 . This excess conductivity is consistent with the two dimensional Aslamazov-Larkin mean-field theory based on the Ginzburg-Landau theory. Applying the Lawrence-Doniach theory, we found that the interlayer coupling stregth is very small, and that a 2D to 3D crossover is not found down to ( T - T c 0 )/ T c 0 = 0.015. This two-dimensional fluctuation seems to be intrinsic to this highly anisotropic layered superconductor.

Thermoelectric power of a single-phase HgBa2Ca2Cu3Oy superconductor

An almost single-phase Hg-1223 superconductor has been prepared and its thermoelectric power (TEP) has been measured as a function of temperature. The sign of the TEP of this material is positive; the TEP shows a sharp increase just above the transition temperature and then decreases slowly; and the zero-crossing of the TEP coincides with the resistive transition temperature, Tc. Two models were applied to explain the anomalous TEP data. One model is based on the modified narrow-band Hubbard system with the additional Fermion contribution and the other is the phenomenological mixed-state model where the localized bound pairs and the delocalized carriers coexist in the normal state. Although both models can fit the semiconductor-like temperature dependence, the latter model takes into account the sharp increase just above the transition temperature.

Fabrication of the HgBa2Ca2Cu3O8+x phase by the ampoule method

Abstract We studied the influence of nominal BaCaCuO precursor composition, prepared by different methods, reaction temperature, mercury and oxygen partial pressures on the formation of the HgBa2Ca2Cu3O8+x phase. High-quality Hg-1223 samples were prepared at 900 °C and nominal mercury gas pressure above 200 atm. X-ray diffraction, SEM/EDX analysis, Auger electron microprobe, TGA, magnetic susceptibility and resistivity measurements were used to characterized the samples.

Synthesis and Superconductivity of the HgBa2Ca2Cu3Ox superconductors

Abstract We produced the HgBa 2 Ca 2 Cu 3 O 8+x (Hg-1223) superconductors by changing the composition, mercury vapor pressure and reaction temperature. We found that the high mercury pressure is essential for the formation of the Hg-1223 phase by preventing the decomposition of HgO at low temperature. This sample was characterized by the X-ray diffraction, Auger electron microprobe, AC susceptibility and resistivity measurement.

The effect of Pr ion concentration on superconducting parameters in Y1−xPrxBa2Cu3O7−δ single crystals

Abstract Y 1− x Pr x Ba 2 Cu 3 O 7−δ single crystals with x = 0.1, 0.2 and 0.3 were grown by the flux method. We analyzed the reversible magnetization with the external field parallel to the c-axis and obtained the various thermodynamic parameters using the Hao-Clem model. Comparing thermodynamic parameters of pure YBa 2 Cu 3 O 7−δ , we discussed the effect of Pr ion on the superconducting properties.

Thermoelectric power of Hg-based superconductors

Abstract Thermoelectric power(TEP) of a single phase Hg-1223 superconductor was measured as a function of temperature. We found several interesting features of the TEP. First, the sign of the TEP is positive. Secondly, the TEP increases sharply just above Tc but demonstrates the semiconductor-like behavior at the normal state. Thirdly, the zero-crossing of the TEP coincides with the resistive transition temperature, Tc. The obvious explaination can be attributed to the phenomenological mixed state of charge carriers. It is clarified by the localized bound pairs and the free carriers in the normal state. This model explains the semiconductor-like temperature dependency, as well as the sharp increase preceding and just above the transition temperature.