Magnetic field effects on $T_c$ 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 $\xi$ fit well with existing experiments. We predict that very near the insulator $\xi$ will rapidly increase. 
Qijin Chen, Ying-Jer Kao, Andrew P. Iyengar, and K. Levin