The expression for the thermal-fluctuation-induced depinning line, T = TP (Be), is derived theoretically for weakly pinning high-Tc superconductors. In the derivation, it is shown that the thermal displacement of pinned fluxoids, uth reduces the critical current density as Jc = Jc0 ( - 〈u2th〉/d2p) 3 2, where Jc0 is the critical current density in the absence of uth and dp is the effective half width of the summed-up pinning potential. Then Tp (itBe) is determined as the temperature at which Jc becomes zero due to the increase of 〈u2th〉 with the increase of T in the external flux density of Be. The relation of Tp(Be) with the irreversibility line of Ti(Be) and the flux melting line of Tm(Be) is also discussed.
!!!All Science Journal Classification (ASJC) codes