METALLIZATION AND 250 K ANOMALY OF HGBR2-INTERCALATED BI-2212 SINGLE-CRYSTALS

The anisotropic resistivity (rho(ab)(T) and rho(c)(T)) and thermoelect ric power (S-ab(T) and S-c(T)) of HgBr2-intercalated Bi-2212 single cr ystals are measured. In the normal state (T > T-c), the semiconductor- like behaviour of rho(c)(T) of the pristine Bi2Sr2CaCu2Oy becomes meta llic upon HgBr2 intercalation, while rho(ab)(T) remains metallic. Unli ke the iodine-intercalated Bi-2212, the semiconductor-like S-ab(T) of the pristine sample changes to be weakly temperature dependent upon Hg Br2 intercalation and yet the S-c(T) remains temperature independent. Resistivity and thermoelectric power data of the HgBr2-intercalated sa mples show anomalies at T = 250 K reminiscent of a phase transition. T he results indicate that the charge transfer from HgBr2 to the CuO2 pl ane is important, which supports the picture that the doping-induced h oles in the copper oxide sheets are responsible for the high-temperatu re superconductivity.