Doping dependence of the critical current properties in Bi_2.2Sr_1.8CaCu₂O₈₊_δ single crystals

In high-T_c cuprate superconductors, the doping (p) dependence of the critical temperature (T_c) and the upper critical field (H_c2) has been intensively investigated to optimize the properties and to elucidate the electronic phase diagram. On the other hand, for the critical current density (J_c), although it is empirically known that J_c increases in the overdoped region, the detailed p dependence has not been established because J_c strongly depends on inhomogeneities such as defects and impurities. Therefore, establishing the detailed p dependence of J_c is expected to provide new insights into optimizing J_c and understanding the electronic phase diagram.

In this study, we focused on Bi₂Sr₂CaCu₂O_8+δ (Bi2212), where p can be tuned over a wide range by controlling the excess oxygen content δ. By repeating the p control and J_c evaluation on the same Bi2212 single crystal sample, the influence of crystal characteristics (chemical composition, defect structure, etc.) on J_c was reduced. Thus, a systematic p dependence of J_c was successfully obtained. Notably, we found that J_c unexpectedly increases in the underdoped region at low temperatures. In the meeting, we will report the results in detail and discuss the possible origin of the enhancement of J_c.