SPLITTING OF THE RESISTIVE TRANSITION OF COPPER-OXIDE SUPERCONDUCTORS- INTRINSIC DOUBLE SUPERCONDUCTING TRANSITIONS VERSUS EXTRINSIC EFFECTS

To prove the possible existence of an intrinsic double superconducting transition in the high-temperature copper oxide superconductors (HTSC ), an effect recently attributed by various groups to different intrin sic properties of these materials (including unconventional wave pairi ng), we present in this paper high resolution data of the electrical r esistivity, p(T), around the superconducting transition of different s ingle crystal and polycrystal YBa2Cu3O7-delta samples. The-analysis of the temperature derivative of these p(T) data strongly suggests that (i) with a temperature resolution well to within 20 mK, the intrinsic resistive transition of the HTSC does not present any double transitio n anomaly and (ii) the double peak structure observed in dp(T)/dT by s ome authors is probably an extrinsic effect (associated with stoichiom etric inhomogeneities in some cases, and with experimental artifacts i n other cases).