Fig. 4.

H-T phase diagram of FeSe for $\mathit{H}\Vert c$. Solid blue and open red circles represent $H_{\text{irr}}$ determined by zero resistivity and the onset of hysteresis loops of the magnetic torque, respectively. The mean-field upper critical field is above $H_{\text{irr}}$. Solid red circles represent $H^{\mathrm{\ast }}$ determined by the cusp of $\kappa \left(H\right)/T$ shown in Fig. 3 B and C, separating a high-field superconducting phase (B phase) from the low-field phase (A phase). (Inset) Overall H-T phase diagram. Superconducting fluctuation regime is determined by the temperature at which the resistivity deviates from the behavior expected in conventional semimetallic systems.