Magnetic Field Effects on Tc and the Pseudogap Onset Temperature in Cuprate Superconductors

We study the sensitivity of Tc and the pseudogap onset temperature, T , to low fields, H, for cuprate superconductors, using a BCS-based approach extended to arbitrary coupling. We find that T ∗ and Tc, which are of the same superconducting origin, have very different H dependences. The small coherence length makes T ∗ rather insensitive to the field. However, the presence of the pseudogap at Tc makes Tc more sensitive to H. Our results for the coherence length ξ fit well with existing experiments. We predict that very near the insulator ξ will rapidly increase.