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 intercalation. The T-c's obtained from the de magnetic susceptibility measurements were plotted against x. The plot of T-c vs x for the pristines showed the parabolic feature with overdoped (0.0 less than or equal to x less 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 compared with nonintercalated samples. Such changes in T-c upon intercalation indicate hole doping from intercalant to host lattice. An attempt of semiempirical calculation was made to determine the hole concentration doped by intercalation. Upon HgBr2 intercalation, the amount of hole 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 depression (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 Delta d approximate to 6.3 Angstrom), it can be concluded that the change in T-c upon intercalation clearly depends on the hole concentration due to the charge transfer between host and guest, rather than the interblock electronic coupling due to the lattice expansion.