Abstract
We perform a detailed comparison of magnetotunneling in conventional low- Nb/Al-AlO/Nb junctions with that in slightly overdoped BiPbSrCaCuO [Bi(Pb)-2212] intrinsic Josephson junctions and with microscopic calculations. It is found that both types of junctions behave in a qualitatively similar way. Both magnetic field and temperature suppress superconductivity in the state-conserving manner. This leads to the characteristic sign change of tunneling magnetoresistance from the negative at the subgap to the positive at the sum-gap bias. We derived theoretically and verified experimentally scaling laws of magnetotunneling characteristics and employ them for accurate extraction of the upper critical field . For Nb an extended region of surface superconductivity at is observed. The parameters of Bi(Pb)-2212 were obtained from self-consistent analysis of magnetotunneling data at different levels of bias, dissipation powers, and for different mesa sizes, which precludes the influence of self-heating. It is found that for Bi(Pb)-2212 is T and decreases significantly at . The amplitude of subgap magnetoresistance is suppressed exponentially at , but remains negative, although very small, above . This may indicate the existence of an extended fluctuation region, which, however, does not destroy the general second-order type of the phase transition at .
1 More- Received 5 May 2011
DOI:https://doi.org/10.1103/PhysRevB.84.054516
©2011 American Physical Society