2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/18087We demonstrate that the observed dependences of $T_c$ and $T^*$ on small magnetic fields can be readily understood in a precursor superconductivity approach to the pseudogap phase. In this approach, the presence of a pseudogap at $T_c$ (but not at $T^*$) and the associated suppression of the density of states lead to very different sensitivities to pair-breaking perturbations for the two temperatures. Our semi-quantitative results address the puzzling experimental observation that the coherence length $ξ$ is weakly dependent on hole concentration $x$ throughout most of the phase diagram. We present our results in a form which can be compared with the recent experiments of Shibauchi et al, and argue that orbital effects contribute in an important way to the $H$ dependence of $T^*$.6 pages, 1 figure, elsart.cls included. Submitted to the proceeding of SNS 2001, ChicagoStrongly Correlated Electronstext