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

We study the sensitivity of T_c 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 T_c, 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 T_c makes T_c 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.