Figure 2

(a) B-T phase diagram of an optimally-doped LSCO. The open circles denote B_c2 measured by using an STC magnet in this study, and the open diamonds (colored in pink) are B_c2s near T_c reported in ref.³⁰. The open squares are B_c2 in the B//c configuration determined by Ando et al.³⁴. The solid line shows the upper critical field of the WHH theory, B_WHH. T_r^* is the temperature at the local maxima of B_WHH(T). The dotted line is a guide for the eye, indicating the critical field of the first-order transition, B_FOT. (b) Enlarged plot of (a). Several B_WHH and B_FOT (guide) are displayed as solid and dotted lines, respectively.