EVOLUTION OF SUPERCONDUCTING TRANSITION-TEMPERATURE (T-C) UPON INTERCALATION OF HGBR2 INTO THE BI2SR1.5-XLAXCA1.5CU2OY

Intercalation of HgBr2 into Bi2Sr1.5-xLaxCa1.5Cu2Oy (0.0 less than or equal to y less than or equal to 0.4) superconductor has been carried out in order to elucidate the origin of T-c evolution upon intercalati on. The T-c's obtained from the de magnetic susceptibility measurement s were plotted against x. The plot of T-c vs x for the pristines showe d the parabolic feature with overdoped (0.0 less than or equal to x le ss than or equal to 0.1), optimally doped (x = 0.1), and underdoped (0 .2 less than or equal to x less than or equal to 0.4) regions. The T-c 's of the HgBr2 intercalates in the overdoped region were reduced less than similar to 6 K but increased by 4-6 K in the underdoped one comp ared with nonintercalated samples. Such changes in T-c upon intercalat ion indicate hole doping from intercalant to host lattice. An attempt of semiempirical calculation was made to determine the hole concentrat ion doped by intercalation. Upon HgBr2 intercalation, the amount of ho le doping was estimated to be similar to 0.2 hole per formula unit of the sample with x = 0.0, whereas the doping of similar to 0.3 hole was estimated for the iodine intercalated sample. Considering the T-c dep ression (Delta T-c) and lattice expansion (Delta d) between the iodine intercalate (Delta T-c approximate to 10 K and Delta d approximate to 3.6 Angstrom) and the HgBr2 one (Delta T-c approximate to 6 K and Del ta d approximate to 6.3 Angstrom), it can be concluded that the change in T-c upon intercalation clearly depends on the hole concentration d ue to the charge transfer between host and guest, rather than the inte rblock electronic coupling due to the lattice expansion.